Designed synthesis of exchange-coupled oximate-based polynuclear complexes / by Sumit Khanra [original]

DESIGNED SYNTHESIS OF EXCHANGE-COUPLED OXIMATE-BASED POLYNUCLEAR

COMPLEXES

DESIGNED SYNTHESIS OF

EXCHANGE-COUPLED OXIMATE-

BASED POLYNUCLEAR

COMPLEXES

Dissertation for the degree of Doktor der

Naturwissenschaften in the Fakultät für

Naturwissenschaften (Department Chemie)

at the Universität Paderborn

Presented by

Sumit Khanra

MÜLHEIM AN DER RUHR, 2005

DESIGNED SYNTHESIS OF EXCHANGE-COUPLED OXIMATE-BASED POLYNUCLEAR

COMPLEXES

This work was independently carried out between June 2002 and April 2005 at

the Max-Planck-Institut für Bioanorganische Chemie, Muelheim an der

Ruhr, Germany.

Submitted on: 08.08.2005 Examination: 16.09.2005

Publications:

1. A Magnetostructural Study of Linear NiIIMnIIINiII, NiIICrIIINiII and Triangular NiII3

Species Isolated from (Pyridine-2-aldoximato)nickel(II) Unit as a Building Block.

Thomas Weyhermüller, Rita Wagner, Sumit Khanra and Phalguni Chaudhuri

Dalton. Trans. 2005, 2539

2. Self-assembly of a Nonanuclear Nickel(II) Complex and its Magnetic Properties

Sumit Khanra, Thomas Weyhermüller, Eva Rentschler and Phalguni Chaudhuri

Inorg. Chem. 2005, 8176

3. Photoinduced Intramolecular Proton Transfer of Phenol-containing Ligands and their

Zn-Complexes.

Helmut Görner, Sumit Khanra, Thomas Weyhermüller and Phalguni Chaudhuri

J. Phys. Chem., 2005, in press

4. Deliberate Synthesis for Magnetostructural Study of Linear Tetranuclear

BIIIMnIIMnIIBIII, MnIIIMnIIMnIIMnIII, MnIVMnIIMnIIMnIV, FeIIIMnIIMnIIFeIII and

CrIIIMnIIMnIICrIII Complexes Using the Idea of “Metal Complexes” as Ligands.

Sumit Khanra, Thomas Weyhermüller and Phalguni Chaudhuri

Inorg. Chem. 2005, Will be submitted soon.

5. A Magnetostructural Study of Butterfly Heterotetranuclear FeIII2CuII2 and CrIII2CuII2

Core Congeners with Strong (O…H…O) Bonding, Generated from [Cu(dapdoH2)]2+

Building Block: Competing Exchange Interaction and Irregular Spin State Structure.

Sumit Khanra, Thomas Weyhermüller and Phalguni Chaudhuri

Inorg. Chem. 2005, Manuscript in preparation

DESIGNED SYNTHESIS OF EXCHANGE-COUPLED OXIMATE-BASED POLYNUCLEAR

COMPLEXES

6. Synthesis, Crystal Structure and Magnetic Properties of an Endogenous-alkoxo and

Exogenous-hydroxo bridged Nonanuclear Copper(II) Metallamacrocyclic Core.

Sumit Khanra, Thomas Weyhermüller, Eva Rentschler and Phalguni Chaudhuri

Dalton Trans. 2005, Manuscript in preparation

7. Tridentate Facial Ligation of Tris (Pyridine-2-aldoximato)nickel(II) to Generate

MnIIINiII, NiIINiII, ZnIINiII and Electrochemically Generated MnIVNiII, MnIINiII, ZnIINiIII ,

NiIINiIII Species : Magnetostructural, Electrochemical, Spectroscopic EPR and MCD

Studies.

Phalguni Chaudhuri, Thomas Weyhermüller, Rita Wagner, Sumit Khanra, Stergios Piligkos,

Eckhard Bill and Eberhard Bothe.

Inorg. Chem. 2005, Manuscript in preparation

Examination Committee:

Prof. Dr. Phalguni Chaudhuri (Referent)

Prof. Dr. G. Henkel(Koreferent)

Prof. Dr. K. Hubber (Prüfer)

Prof. Dr. W. Bremser (Vorsitzender)

Examination: 16.09.2005

DESIGNED SYNTHESIS OF EXCHANGE-COUPLED OXIMATE-BASED POLYNUCLEAR

COMPLEXES

Acknowledgements

I would like to mention that submission of this thesis of mine would not have been possible at all

had I not been bestowed with the benign association of the scientific elite of the Max Planck

Institute, Muelheim an der Ruhr, Germany.

First of all, I humbly offer my deepest obeisance to Prof. Dr. P. Chaudhuri, who offered me the

scope to be one of the Research- scholars under him. His constant guidance, hour-long invaluable

discussions, perpetual inspiration with occasional reformatory thrashings always acted as

motivating factors to my research works. Prof. Dr. P. Chaudhuri, in the truest sense, played the

ideal role of the philosopher, the friend and the guide to me.

I am very much thankful to Prof. Dr. K. Wieghardt for the opportunity of working in his

research group, providing with all needed laboratory facilities and also for intricate scientific

discussion, invaluable guidance.

I am very much indebted to Dr. E. Bill for extending his warm hand for me in the field of

Molecular Magnetism. Hour- long discussions with him on some intricate scientific issues infused

a sense of confidence in me to complete this thesis.

I am indebted to Dr. T. Weyhermüller and Mrs. H. Schucht for their elegant work with the X-

ray crystallography.

I cannot do justice to myself unless I acknowledge the contribution of Prof. Dr. E. Rentschler,

Universität Mainz, Germany, who in spite of her busy schedule, spent her valuable time to teach

and help me to simulate magnetic data for polynuclear complexes by ITO formalism

Thanks to Dr. E. Bothe and Mrs. P. Höfer for their help during electrochemical measurements,

discussions and fruitful suggestions.

Dr. J. F. Barry and Dr. P. Larsen for suggestion and correction to complete this thesis.

I am thankful to Mr. A. Göbels, Mr. F. Reikowski, and Mr. B. Mienert for discussions and

measurements of EPR, SQUID, and Mössbauer.

DESIGNED SYNTHESIS OF EXCHANGE-COUPLED OXIMATE-BASED POLYNUCLEAR

COMPLEXES

I am thankful to Frau. R. Wagner and Herr. U. Pieper, for technical assistance in the laboratory

and due to their suggestions.

Mrs U. Westhoff and Mrs. M. Trinoga for skillfull GC and LC analysis.

Frau J. Theurich, Frau. B. Deckers and Herr W. Schlamann for their helpfulness in general.

Dr. K. Chlopek, Dr. L. Slep, Dr. K. Merz, Dr N. Aliaga-Alcalde, Dr. L. Benisvy, Dr Y. Song,

Dr. S. Piligkos, and S. Kokattam, for a cordial working atmosphere and invaluable friendship.

Dr. Apurba Patra, Amin Khan, Shivani, Chandan Mukherjee, Dr. Kallol Ray, Dr. Tapan Paine,

Dr. Soumen Mukherjee, Dr. Sourav Chaterjeee, Mamtha, for a nice homely atmosphere outside

the laboratory and a wonderful friendship that I will cherish forever.

I will ever be thankful to Dr. Ruta Kapre and Dr. Sachin Kinge for a friendship and help that

will remain in my heart for ever. Ruta and Sachin, thanks for being such nice friends.

Family Basak and Shila to make the life easier in Mülheim an der Ruhr.

Nivedita and Iowanna for wonderful friendship and encouragement.

I am thankful to my Parents, Parents in law, Amit and Ananda for their constant inspiration and

encouragement.

I am highly indebted to my wife Suchismita for her understanding, inspiration, invaluable

support and having faith in me.

DFG and MPG are greatfully acknowledged for financial assistance

Last but not the least in the list of my well wishers and aides, is the convoy

of my research- mates in this Institute, my friends and fraternities outside, who stood by me in my

weal and woe during my academic career in the Max Planck Institute for Bioinorganic Chemistry,

Muelheim, Germany.

DESIGNED SYNTHESIS OF EXCHANGE-COUPLED OXIMATE-BASED POLYNUCLEAR

COMPLEXES

CONTENTS

ABSTRACT

CHAPTER 1

INTRODUCTION AND OBJECTIVES

1.1 BACKGROUND 1

1.2 OBJECTIVES 2

1.3 REFERENCES 16

CHAPTER 2

TRINUCLEAR METAL OXIMATES: DESIGNED SYNTHESIS AND MAGNETIC

PROPERTIES OF LINEAR NiIIMnIIINiII, NiIICrIIINiII AND TRIANGULAR NiII3

COMPLEXES

2.1 INTRODUCTION 21

2.2 SYNTHESIS 22

2.3 INFRARED AND MASS SPECTROSCOPY 22

2.4 X-RAY CRYSTAL STRUCTURE

2.4.1 Molecular Structure of [NiII(PyA)3MnIII(PyA)3NiII](ClO4) 23

2.4.2 Molecular Structure of [NiII(PyA)3CrIII(PyA)3NiII](ClO4) 25

2.4.3 Molecular Structure of [NiII3(PyA)5(PyAH)](ClO4) 26

2.5 MAGNETISM 30

2.6 REFERENCES 35

CHAPTER 3

MIXED VALENCE LINEAR HOMO AND HETERO TETRANUCLEAR

BIIIMnIIMnIIBIII, MnIIIMnIIMnIIMnIII , MnIVMnIIMnIIMnIV, FeIIIMnIIMnIIFeIII,

CrIIIMnIIMnIICrIII COMPLEXES : A MAGNETOSTRUCTURAL STUDY

3.1 INTRODUCTION 39

3.2 SYNTHESIS 40

3.3 INFRARED AND MASS SPECTROSCOPY 42

3.4 X-RAY CRYSTAL STRUCTURE

3.4.1 Molecular Structure of [(MeB)2MnII2(dfmp)3](Et3NH) 43

3.4.2 Molecular Structure of [(Me3TACN)2 MnIII2MnII2(dfmp)3](ClO4) 44

3.4.3 Molecular Structure of [(Me3TACN)2 MnIV2MnII2(dfmp)3](ClO4)3 46

3.4.4 Molecular Structure of [(Me3TACN)2 FeIII2MnII2(dfmp)3](ClO4) 48

DESIGNED SYNTHESIS OF EXCHANGE-COUPLED OXIMATE-BASED POLYNUCLEAR

COMPLEXES

3.5 MÖSSBAUER SPECTROSCOPY 50

3.6 ELECTROCHEMISTRY 51

3.7 MAGNETISM 52

3.8 REFERENCES

CHAPTER 4

HETEROTETRANUCLEAR [FeIII2CuII2], [CrIII2CuII2] BUTTERFLY CORE

CONGENERS

4.1 INTRODUCTION 65

4.2 SYNTHESIS 66

4.3 INFRARED AND MASS SPECTROSCOPY 67

4.4 X-RAY CRYSTAL STRUCTURE

4.4.1 Molecular structure of [(Me3TACN)2FeIII2(dapdo)2CuII2(O...H...O)Cl](ClO4)2 68

4.4.2 Molecular Structure of [(Me3TACN)2CrIII2(dapdo)2CuII2(OH)2Br2](ClO4)2 71

4.5 MAGNETISM 74

4.6 REFERENCES 85

CHAPTER 5

HIGH SPIN STAR SHAPED MnII4 AND TETRAHEDRAL MnIII4 MOLECULES

5.1 INTRODUCTION 89

5.2 SYNTHESIS 90

5.3 INFRARED AND MASS SPECTROSCOPY 91

5.4 X-RAY CRYSTAL STRUCTURE

5.4.1 Molecular Structure of [MnII4(ppi)6](BF4)2 92

5.4.2 Molecular Structure of [MnIII4(salox)4(salox H)4] 95

5.5 MAGNETISM 98

5.6 REFERENCES 108

CHAPTER 6

MIXED-VALENCE HEXANUCLEAR MANGANESE COMPLEXES OF

[MnII2MnIII4O2]12+ AND HEXANUCLEAR COPPER COMPLEX OF

[CuII3O...H...OCuII3]9+ CORE CONGENERS

6.1 INTRODUCTION 113

6.2 SYNTHESIS 114

6.3 INFRARED AND MASS SPECTROSCOPY 115

DESIGNED SYNTHESIS OF EXCHANGE-COUPLED OXIMATE-BASED POLYNUCLEAR

COMPLEXES

6.4 X-RAY CRYSTAL STRUCTURE

6.4.1 Molecular Structure of [MnII2MnIII4(µ4-O)2(µ2-OH)2L2(LH)4](ClO4)2 115

6.4.2 Molecular Structure of [MnII2MnIII4(µ4-O)2(µ2-OMe)2L2(LH)4](ClO4)2 119

6.4.3 Molecular Structure of [CuII6(µ3-O)(µ3-OH)L13(H2O)6](BF4)3 121

6.5 MAGNETISM 124

6.6 REFERENCES 136

CHAPTER 7

TWO RARE EXAMPLES OF NONANUCLEAR NICKEL(II) AND COPPER(II)

COMPLEXES

7.1 INTRODUCTION 141

7.2 SYNTHESIS 143

7.3 INFRARED AND MASS SPECTROSCOPY 144

7.4 X-RAY CRYSTAL STRUCTURE

7.4.1 Molecular Structure of [NiII9(PyA)10(µ3-OH)2(µ2-OH)2((µ2-OH2)2(H2O)6](ClO4)4 145

7.4.2 Molecular Structure of [CuII9L4(µ3-OH)4(MeOH)2](ClO4)2 149

7.5 MAGNETISM 154

7.6 REFERENCES 163

CHAPTER 8

CONCLUSIONS AND PERSPECTIVES 167

CHAPTER 9

EQUIPMENT AND EXPERIMENTAL WORK

9.1 METHODS AND EQUIPMENTS 183

9.2 SYNTHESIS

9.2.1 LIGANDS 185

9.2.2 COMPLEXES 187

APPENDICES

(1) CRYSTALLOGRAPHIC DATA 205

(2) MAGNETOCHEMICAL DATA 211

(3) CURRICULAM VITAE 228

DESIGNED SYNTHESIS OF EXCHANGE-COUPLED OXIMATE-BASED POLYNUCLEAR

COMPLEXES

ABBREVIATIONS

Abbreviations:

Technical terms:

AF: antiferromagnetic

Ag / AgNO3: reference electrode

av.: average

B: magnetic field

CT: charge transfer

D: zero-field splitting

deg.: degree (°)

e- : electron

E: total energy

exp.: experimental

F: ferromagnetic

fac.: facial

Fc+/Fc: internal electrochemical standard

g: Landé factor

H: Hamiltonian

h.s: high spin

I: nuclear spin

IS: intermediate spin

J: coupling constant ( cm-1)

KD: Kramer doublet

LF: ligand field

m/z: mass per charge

[M]+: molecular ion peak

M: molar magnetization

mer.: meridional

MP: melting point

PI: paramagnetic impurity

rt: room temperature (293K)

S: electron spin

sim: simulated

TIP: temperature independent paramagnetism

ZFS: zero-field splitting

Techniques:

CV: cyclic voltammetry

EA: elemental analysis

ABBREVIATIONS

EI: electron ionization

EPR: electron paramagnetic resonance

ESI: electrospray ionization

IR: infrared spectroscopy

LC: liquid chromatography

MS: mass spectroscopy

NMR: nuclear magnetic resonance

SQUID: superconducting quantum interface device

SW: square wave voltammetry

UV-Vis: ultraviolet-visible spectroscopy

VTVH: Variable-temperature variable field

Units:

Å: angstrom (10-10 m)

cm: centimeter

emu: electromagnetic unit

G: gauss

K: Kelvin

M : molar

mm : millimeter

nm : nanometer (10-9 m)

ppm: parts per million

s: second

T : tesla

V : volts

µB : bohr magnetron

Latin expressions:

ca.: around

et al: and coworkers

e.g.: for example

i.e.: namely

vs.: versus, against

Symbols:

λ: wavelength (nm)

ε: extinction coefficient (M-1cm-1)

IS: isomer shift (mms-1)

µeff: magnetic moment (µB)

∆EQ: quadrupole splitting (mm/s)

ABBREVIATIONS

ιι

δ: isomer shift (mm/s)

Solvents and reagents:

Bu4NOMe : tetrabutylammoniummethoxide

Et3N: triethylamine

TBAPF6: tetrabutylammonium hexafluorophosphate

TMS: tetramethylsilane

[9]-aneN3: triazacyclononane = 1,4,7-triazacyclononane

Me3Tacn: tmtacn = 1,4,7-trimethyl-1,4,7-triazacyclononane

Ligands used in this work:

PyAH: syn-2-pyridine-aldoxime

SaloxH2: salicylaldoxime

DapdoH2: 2,6-diacetylpyridyl dioxime

DfmpH3: 2,6-diformyl-4-methyl phenol dioxime

Hppi: 2-pyridylmethyl-2-hydroxyphenylimine

H2L: dioxime from m-xylenediamine

H3L1: N,N’-(2-hydroxypropane-1,3-diyl)bis(benzoylacetoneimine)

List of complexes synthesized with their numbers:

[NiII(PyA)3MnIII(PyA)3NiII](ClO4) (1)

[NiII(PyA)3CrIII(PyA)3NiII](ClO4) (2)

[NiII3(PyA)5(PyAH)](ClO4).CH3CN (3)

[MeB{dfmp)3MnIIMnII}BMe](Et3NH) (4)

[(Me3Tacn)MnIII{dfmp)3MnIIMnII}MnIII(Me3Tacn)](ClO4) (5)

[(Me3Tacn)MnIV{dfmp)3MnIIMnII}MnIV(Me3Tacn)](ClO4)3 (6)

[(Me3Tacn)FeIII{dfmp)3MnIIMnII}FeIII(Me3Tacn)](ClO4) (7)

[(Me3Tacn)CrIII{dfmp)3MnIIMnII}CrIII(Me3Tacn)](ClO4) (8)

[(Me3Tacn)2FeIII2(dapdo)2CuII2(O..H..O)Cl] (ClO4)2 (9)

[(Me3Tacn)2CrIII2(dapdo)2CuII2(OH)2Br2] (ClO4)2 (10)

[MnII4(ppi)6](BF4)2 .2CH3CN. H2O (11)

[MnIII4(salox)4(salox H)4] .2.5 CH3OH (12)

[(dapdo)2(dapdoH)4[(µ-O)2(µ-OMe)2MnIII4MnII2](ClO4)2 (13)

[(dapdo)2(dapdoH)4[(µ-O)2(µ-OH)2MnIII4MnII2](ClO4)2 (14)

[L3(µ-O..H..O-µ)CuII6(H2O)6](BF4)3 (15)

[NiII9(PyA)10(µ3-OH)2(µ2-OH)2(µ2-OH2)2(H2O)6](ClO4)4 .12 H2O (16)

[CuII9L4(µ3-OH)4(MeOH)2](ClO4)2 .6 MeOH (17)

ABBREVIATIONS

ϖιιι

ABSTRACT

OUTLINE OF THE THESIS

The principles of coordination chemistry e.g. ligand field theory constitute a common

ground for molecular magnetism, biomimetics and bioinspired chemistry. The subject of

molecular magnetism is the center of this thesis. Summarily, this thesis mainly describes

exchange-coupled homo and heteropolynuclear complexes, containing different

paramagnetic metal ions, with particular emphasis on the interactions of spin carriers

based on different topological approach with irregular spin state structures towards

building high-spin molecules. These polynuclear complexes described here are

characterized structurally and spectroscopically so that magnetostructural correlations

can be made.

This work is divided into eight chapters. The first chapter gives an introduction

relevant to this work, considering the background of "Molecular Magnetism" and the

importance of the exchange coupled polynuclear complexes in “molecular magnetism”

and magnetic molecular materials. The importance of oxime ligands as backbones for

polynuclear complexes due to their versatility at bonding modes is discussed. A few

examples of well characterized high spin molecules, relevant to this thesis, are reviewed.

The second chapter is concerned with the synthesis, characterization and

magnetostructural study of exchange coupled trinuclear oximate complexes. It is to be

mentioned here that new exchange pathways can be expected for heteropolynuclear

complexes where unusual sets of magnetic orbitals can be made to overlap with each

other and hence investigations of a series of heteropolynuclear complexes might be more

informative in comparison to those of homometal complexes. Three trinuclear

complexes, NiIIMnIIINiII 1, NiIICrIIINiII 2 and NiII3 3 based on (pyridine-2-

aldoximato)nickel(II) units are described. Two of them, 1 and 2, contain metal-centers in

linear arrangement, as is revealed by X-ray diffraction. Complex 3 is a homonuclear

complex in which the three nickel(II) centers are disposed in a triangular fashion. The

compounds were characterized by various physical methods including cyclic

voltammetric and variable-temperature (2–290 K) susceptibility measurements.

Complexes 1 and 3 display antiferromagnetic exchange coupling of the neighboring

metal centers, while weak ferromagnetic spin exchange between the adjacent NiII and

CrIII ions in 2 is observed. The experimental magnetic data were simulated by using

appropriate models.

The third chapter presents linear tetranuclear “homo and heteropolymetallates”

constructed using a dinucleating oxime ligand. One dinuclear and four tetranuclear

ABSTRACT

complexes, MnIIMnII 4, MnIIIMnIIMnIIMnIII 5, MnIVMnIIMnIIMnIV 6,

FeIIIMnIIMnIIFeIII 7 and CrIIIMnIIMnIICrIII 8 based on (2,6-diformyl-4 methyl

phenoldioximato)manganese(II) units are described. All of them contain metal-centers in

linear arrangement, as is revealed by X-ray diffraction. The compounds were

characterized by various physical methods including cyclic voltammetric and variable-

temperature (2–290 K) susceptibility measurements. Complexes display overall

antiferromagnetic exchange coupling with extremely low-lying states.

The fourth and fifth chapters discuss the building up of high spin polynuclear

complexes based on different molecular topology such as, butterfly, star-shaped etc, and a

“parallel spin coupled” system using “accidental ferromagnetism” and “planned

ferromagnetism” both governed by the common principle of orthogonal orbital overlap. It

also discusses irregular spin state structures due to spin frustration or competing

exchange interaction. Two tetranuclear complexes, FeIII2CuII2 9, CuII2CrIII2 10 based on

(2,6-diacetyl pyridinealdoximato)copper(II) units and Me3TacnMX3 (where M = Fe(III),

Cr(III) and X = Cl or Br) are described. Both of them, 9 and 10, contain metal-centers

disposed in "butterfly" fashion with M(III) as the "wing" and Cu(II) as the "body", as is

revealed by X-ray diffraction. The compounds were characterized by various physical

methods including variable-temperature (2–290 K) susceptibility and variable-

temperature variable-field (VTVH) magnetic measurements. The experimental magnetic

data were simulated by using appropriate models Complexes 9 and 10 display

antiferromagnetic exchange coupling of the neighboring metal centers, due to the "spin-

frustration" or more precisely competing exchange interactions between the spin carriers

complex 10 exhibits irregular spin state structure with ST = 2 ground state. While strong

wing-body interactions over body-body interaction, stabilizes ST = 4 ground state in

complex 9.

Two tetranuclear complexes, MnII4 11, MnIII4 12 based on salicylaldoxime ligand

are described. One of them, 11 contains metal-centers in "star-shaped" arrangement while

the complex 12 in which the four manganese(III) centers are disposed in a tetrahedral

fashion, as is revealed by X-ray diffraction. The compounds were characterized by

various physical methods including variable-temperature (2–290 K) susceptibility and

variable-temperature variable-field (VTVH) magnetic measurements. The experimental

magnetic data were simulated by using appropriate models Complexes 11 and 12 display

weak ferromagnetic exchange coupling of the neighboring metal centers, and yield high-

spin ST = 10 and ST = 8 ground states for the complexes 11 and 12 respectively.

ABSTRACT

ιι

Also hexa-and nonanuclear complexes have been synthesized and are described

in chapters six and seven. The hexanuclear complexes, composed of two edge-sharing

triangular units, are also subjected to magnetostructural studies as described in chapter

five, while sixth chapter describes two rare examples of nonanuclear Ni(II) and Cu(II)

complexes. Two nonanuclear complexes, NiII9 16, CuII9 17 based on (pyridine-2-

aldoximato)nickel(II) unit and N,N'-(2-Hydroxypropane-1,3-

diyl)bis(benzoylacetoneimine) respectively are described. Both of them, 16 and 17,

contain two irregular tetrahedra connected to a centrally placed M(II) ions, as is revealed

by X-ray diffraction. The compounds were characterized by various physical methods

including variable-temperature (2–290 K) susceptibility measurements and variable-

temperature variable-field (VTVH) magnetic measurements. Complexes 16 and 17

display antiferromagnetic exchange coupling of the neighbouring metal centers. The

experimental magnetic data were simulated by using appropriate models.

ABSTRACT

ϖιιι

CHAPTER 1

CHAPTER -1

INTRODUCTION AND OBJECTIVES

1.1 Background:

Molecular magnetism1,7,15 is a field of research where the investigation of the

magnetic properties of isolated molecules as well as of assemblies of molecules is

undertaken. These molecules may contain one or more magnetic centers. Assemblies of

molecules occurring in the solid state may be characterized by weak interactions between

the molecular entities, thus displaying magnetic behavior very similar to that of the

isolated molecules or may consist of extended systems built from molecular precursors in

a way that maximizes the interactions between these molecular precursors, yield bulk

magnetic properties. Solid state systems (metal oxides or metallic compounds) that also

display highly interesting magnetic properties but do not consist of molecular entities or

do not derive from molecular precursors are not included within the framework of the

definition on molecular magnetism. In molecular magnetism the magnetic properties of

paramagnetic molecules and how these properties affect the bulk magnetic properties of

molecular materials are described.

This field concerns the chemistry and the physics of open shell molecules and molecular

assemblies containing open-shell units. The main facets of molecular magnetism may be

summarized as follows:

(i) Designing of open-shell molecules, the main emphasis being on molecules containing

at least two magnetic centers where spin communication is possible between the spin

carriers. These spin carriers may be transition metal ions as well as organic radicals.

Efforts will be given to the design of polynuclear complexes containing tri, tetra and even

if higher nuclearity spin clusters of transition metal ions.

(ii) Determination of the spectra of the low-lying states for such open-shell molecules,

using various techniques such as magnetic susceptibility and magnetization

measurements, EPR and optical spectroscopies or inelastic neutron scattering.

(iii) Chemistry and physics of transition metal compounds exhibiting a spin conversation

or spin-transition between two different spin states.

(iv) The relations among magnetic properties, structure and reactivity of metalloenzymes

and model compounds. This facet may be defined as biomagnetism.

INTRODUCTION AND OBJECTIVES

(v) Three-dimensional effects in molecular assemblies, containing open-shell units. The

main issues deal with molecular-based compounds exhibiting a spontaneous

magnetization below a critical temperature Tc.

A prominent site of molecular magnetism is its interdisciplinary nature. It has already

been pointed out that molecular magnetism has common frontiers with quite a few other

areas such as supramolecular chemistry, theoretical chemistry and physics, material and

life sciences and also molecular electronics.

Certainly the subject of "Molecular magnetism" has become increasingly accessible in

recent years through many authoritative reviews and books.1-11 As basic ideas and

concepts related to magnetic interactions are described in these excellent reviews and

books, we refrain here from repeating the same. Instead a description of the concepts of

"spin-frustration", "irregular spin-state structure",16,19 "molecular topology" etc. which

are directly related to this research, is presented.

1.2 Objectives:

The objectives underlying the thesis are:

(i) Designed Synthesis:

One of the challenges in the field of exchange coupling in polymetallic systems is

the design of complexes with predicted magnetic properties. To achieve this goal, the

influence of parameters such as the symmetry of magnetic orbitals, the nature of bridging

and terminal ligands, and changes in coordination geometry have been studied.12

Surprisingly, very few studies of the influence of the molecular topology26 on the

magnetic properties of coordination complexes have been performed. For example, the

chromium analogue of the Werner's hexol, [CrIII{(OH)2CrIIIen2}3](ClO4)6 by Anderson

and Berg exhibits a high-spin ST = 3 ground state owing to its topology,25,26 shown

below.

A ferromagnetic-like behavior is obtained with a ground state characterized by a

large spin, although the interaction between nearest neighbor CrIII ions (SCr = 3/2) is

CHAPTER 1

antiferromagnetic. This effective ferromagnetic coupling between the outer ions is highly

interesting in the context of synthesizing "high spin" molecules. The best result would be

obtained in a topology, in which a maximum number of spins point in the same direction

as show in the previous page. Similarly other tetranuclear complexes of the formula

[{Cu(oxpn)}3Mn](ClO4)2.2H2O by Lloret et.al24a and [Cr(ox){Ni(Me6-(14)ane-

N4)}3](ClO4)3 abbreviated as Cu3Mn and CrNi3 respectively, by Kahn et. al exhibit ST =1

and ST = 9/2 ground state, respectively and it is to be noted that in case of Cu3Mn,

however, the pairwise interaction is antiferromagnetic but stabilizes a nondiamagnetic

ground state due to the topology described above.

Recently more exciting result appeared, dealing with homometal tetranuclear

nickel(II) planar trigonal-shaped species30 [Ni4(HL)3](ClO4)2 where H3L is 1,4,7-

tris(acetophenoxime)-1,4,7-triazacyclononane. This tetranuclear nickel (II) complex with

local spins SNi = 1 exhibits antiferromagnetic exchange interaction and yields a high-spin

ground state ST = 2 owing to the topology of the spin carriers as shown in the Figure

above.

The other two topological possibilities for tetranuclear complexes, namely the

square and the linear arrangements of the spin carriers, lead in the case of identical metal

ions, to a diamagnetic ground state due to the equal number of spins in each direction, as

illustrated schematically below

Thus the challenge for the chemists is to design real molecules having the follo-

wing topologies for polymetallic complexes containing n paramagnetic ions, where n = 3,

4 or 5.

INTRODUCTION AND OBJECTIVES

If the two border cases are considered for a heterometallic system, two possible

situations arise for the spin coupling: i) the smaller spins may be located outside with the

large spin at the center, yielding an overall "low spin“ground state, in which the outer

spins partially cancel the central spin and ii) the reverse arrangement, i.e. the larger spins

outside; the smaller spin located at the center polarizes the outer spins, thus resulting in a

"high spin" ground state. Chaudhuri et.al used this strategy in the synthesis of a linear

trinuclear FeIIICuIIFeIII complex27 with an ST = 9/2 ground state, demonstrating the point

of molecular topology is a very important factor determining the magnetic properties of

polynuclear complexes with more than two metal ions. It is noteworthy that the actual

geometry does not govern the spin structure for n > 3 metal ions. Thus it is possible to

tune the magnetic properties of polynuclear complexes by controlling the topology and

the nature of the ions in interaction. This approach is particularly promising for the

synthesis of "high spin" molecules and needs systematic exploration.

In the field of magnetic molecular materials, one of the main challenges is the

design of molecular ferromagnets. One approach to this consists of first synthesizing

molecular entities with a large spin in the ground state and then of assembling this

molecules within the crystal lattice in a ferromagnetic fashion. One strategy to obtain

ferromagnetic interactions within a molecular entity is to make use of the orthogonality of

the magnetic orbitals of the interacting magnetic centers. These symmetry requirements

are difficult to achieve. Another strategy based on the concept of irregular spin state

structures19 leads to new molecular systems with a large spin in the ground state. It must

be emphasized that the former strategy of orthogonality is not more efficient than the

latter.

The basic idea of an irregular spin state structure can be described in the following way:

The two 5/2 local spins on the terminal iron(III) ions, for example, are aligned along a

common direction through the antiferromagnetic interaction with the central local spin 1/2

of the copper(II) ion, which is depicted below:

CHAPTER 1

+5/2 +5/2

-1/2

Fe Cu Fe

In some way, the small central spin polarizes the two large terminal spins in a

ferromagnetic-like fashion. It is to be noted that J13, the exchange interaction between the

two terminal paramagnetic centers, has a profound effect on the spin-state energy-

splitting pattern and depending on its magnitude a variability of the ground state might

result. The spin-level ordering is a result of the mutual influence of two different

interactions, J12 = J23 and J13, which may lead to "ground-state variability".31a

The key point is to focus on the bridging ligands which have already allowed the

design of molecular based magnets. To date, these bridges are oxamato, oxamido,

oxalato, oximato, carboxylato and cyano. Certain complexes involve such as in Fig. (a)

organic bridging ligand between two similar or dissimilar modules. In (b) and (c) two

mononuclear dissimilar modules generate heterobinuclear entities, in (d) a single metal

ion acts as bridge between two mononuclear subunits giving rise to linear symmetric

heterotrinuclear species. The same approach is used in (e) and (f), but in these cases the

central metal ions are coordinated in bridging ligands producing heterotri and-

tetranuclear complexes. Case (g) demonstrates the schematical presentation of two

modules connected in a butterfly fashion.

These large, mostly linear polynuclear species received the name baukasten or

modular complexes. The ligands facially bonded to the terminal ions are called end-caps,

whereas the intermediate ones are referred to as bridging ligands. The most frequently

encountered building blocks for modular synthesis have been described previously in the

review article by chaudhuri, 30 and some of the pertinent concepts are described below.

INTRODUCTION AND OBJECTIVES

Figure 1.1: Schematical drawings of dinuclear (a-c), trinuclear (d, e) and tetranuclear (f, g) homo-and

heterometal complex.

The synthetic organization of paramagnetic metal centers into close spaced arrays with

useful magnetic properties is a challenge, and is generally achieved by having small

bridging groups, which produce extended 2D and 3D structural arrangements. Cyanide

has proven to be useful in this regard and with orthogonally connected metal orbitals,

long range ferromagnetic ordering can be achieved. The optimal organization of

paramagnetic transition metal centers into extended bridge structures with very short

metal ion spacing can only be achieved with single atom bridges; this can be approached

with e.g., oxygen based bridges. The last few years have experienced the ongoing

development in the area of small 2D arrays with many examples of [3 X 3] magnetic

grids with Co(II), Cu(II) and Mn(II), where M...M separations are of the order of 4Å . [2

X 2] self assembled FeII4 grid reported by Lehn, based on a pyramidine bridging

framework shows novel spin crossover behavior induced by pressure, temperature or

light perturbations. These important unit molecule attributes can only be exploited if

individual molecules can be successfully synthesized.

The oxamide dianion can adopt bidentate and bis bidentate coordination modes in its

metal complexes, like the parent oxalate, to yield polynuclear complexes39. The strong

electron donating capability of its deprotonated nitrogen amide atoms accounts for the

CHAPTER 1

greater stability of its metal complexes when comparing with those of the oxalate.

Moreover the lower electro negativity of the nitrogen atoms with respect to the oxygen

atoms allows for stronger magnetic interactions between metal centers through oxamidato

bridging ligands and several polynuclear complexes of this kind of ligand have been

reported with magnetostructural studies. On the other hand, bimetallic oxamidato-bridged

complexes are well known in magnetochemistry because they are suitable candidates in

designing molecular based magnets.

Metal oximates have proven to be versatile for this approach as will be

evident from the structurally and magnetochemically characterized compounds described

later. The dimensions of structurally characterized oxime groups involve a C=N distance

of ~ 1.26-1.28 Å and a N-O distance of 1.36-1.42 Å. The vicinal groups in solids are

stabilized by the presence of C=N-O....H-O-N=C hydrogen bonds and the C-N-O angles

vary from 110 to 114°. There are different modes of bonding in oxime complexes, these

modes emerge from the potential ambidentate character through nitrogen and/or oxygen

coordination. Some of the bonding modes are depicted in the Figure 1.2 below:

MNOM´

(1)

MNO

M´´

M´

(2)

(3)

(4)

(5)

Figure 1.2: Bonding modes in oximes.

Due to this versatility of bonding modes, oximes are excellent bridging units

in modular synthesis. In the last few years, the idea of synthesizing polynuclear

complexes involving "metal oximates" as building blocks has become quite popular. The

modular preparation with oximato ligands enables the synthesis of linear symmetrical and

INTRODUCTION AND OBJECTIVES

asymmetrical cores MAMA,30,32 M

AMB,30,32 M

AMBMA,27,31a-b MAMBMBMA36 (MA, MB

being two different metal ions). The synthesis of asymmetric heterotrinuclear complexes

MAMBMC and of MA(µ3-O)2 MB butterfly cores have also been achieved. The uniqueness

of oximates providing diatomic N-O-bridging is demonstrated by several series of

isostructural complexes with different metal ions like Cr(III), Mn(III), Mn(IV), Fe(III),

Co(III). Such isostructural series30 are not available for any other bridging ligands.

Several different end-cap ligands have been reported. The function of such

ligands is to prevent undesired oligomerization processes. Many acyclic polyamines

including di-, tri-, and tetra-amines and bipyridine have been used as end cap ligands due

to their ready commercial availability. Although not so readily available and obtainable

only by a lengthy multistep synthesis, a very versatile end-cap ligand is the cyclic amine

1,4,7- trimethyl-1,4,7-triazacyclononan (Me3Tacn). This amine is a facially coordinating

tridentate nitrogen ligand and a significant number of both thermodynamically and

kinetically, stable complexes of this ligands are known.27, 30,31a-b

The synthesis and characterization of homo and heteropolynuclear complexes

with Me3Tacn and oxime ligands using a modular approach has been one of the main

goal of Chaudhuri and coworkers in recent years. Emphasis is given to the structural and

CHAPTER 1

magnetochemical characterization. Recently it has been reported32 that tris(pyridine-2-

aldoximato) metallates, [MII(L)3]-, are capable of acting as ligands to give rise to various

asymmetric dinuclear complexes [(Me3Tacn)MIII(L)3MII]2+ where MIII = Cr(III), Mn(III)

or Fe(III) and MII = Mn(II), Fe(II), Ni(II), Cu(II) and Zn(II) containing three oximato

groups (=N-O) as bridging ligands, which can mediate the exchange interactions of

varying range.

The oxime bridged tetranuclear complexes reported until now are of two types:

(i) Linear tetranuclear complexes are relatively rare. Using a modular synthesis some

examples of MAMBMBMA and MAMAMAMA type containing the dinucleating oxime

were synthesized.36

Polynucleating ligands, on the other hand, have structural attributes that combine

separate coordination pockets, and in cases where they are contiguously arranged, metal

ions are bound in close proximity and can be linked directly by endogenous or exogenous

ligand fragments, leading to spin communication between metals. The interest in

polynuclear complexes started with a class of dinucleating phenol containing ligands,

where the dinucleating phenol provides an ideal focus for the simultaneous coordination

INTRODUCTION AND OBJECTIVES

of two metal ions in close proximity and in further extension by the deprotonation of the

dioximate oxygen to bind more metal ions for the modular synthesis of linear tetranuclear

complexes in designed way.

Compounds with FeIIINiIINiIIFeIII and MnIIINiIINiIIMnIII cores, reported36 earlier are

similar to MnIIIMnIIMnIIMnIII, MnIVMnIIMnIIMnIV, FeIIIMnIIMnIIFeIII and

CrIIIMnIIMnIICrIII congeners (Chapter-3)

(ii) Butterfly structures with the cores [(MA)2(µ3-O)2(MB)2]8+ and [(MA)4(µ3-O)2]8+

So far the reported tetranuclear butterfly clusters are based on homonuclear

tetramanganese and tetrairon cores. Recently heterotetranuclear butterfly cluster was

reported by Chaudhuri and coworkers in connection with magnetostructural correlation

studies. And a series of exchange coupled homo and hetero tetranuclear butterfly clusters

with [Fe4O2]8+, [Mn4O2]8+, [Fe2Mn2O2]8+ cores congeners were structurally and

magnetochemically characterized.37 Although the intrinsic interaction between the body

manganese ions of the butterfly is antiparallel in nature, there is frustration in the spin

alignment or competing interaction in the cluster associated with two manganese ions,

causing the alignment to be parallel and gives rise to ground state variability.

So due to the lack of studies on heteronuclear butterfly clusters it allows

us to investigate such ground state variation of the cluster based on small local spins at

the body and higher local spins at the wing to have some "high spin" molecules due to the

spin frustration or competing spin interaction. In this context some success was achieved

in synthesizing and characterizing such heteronuclear "high spin" complexes and the

competing spin interaction and irregular spin state structures will be described.

CHAPTER 1

High nuclearity clusters with more than four metal centers were analyzed

previously in our group with oxime ligand. An example is the hexanuclear cluster

comprised of two µ3-oxo centred trinuclear [CrIII3(µ3-O)] units.38 The antiferromagnetic

coupling between the CrIII centers reported in the literature is around - 14.0 cm-1( H = -

2JSiSj), where exchange interaction was mediated through µ-oxo, oximate (=N-O) and

also through the carboxylate bridging.

Further success was achieved in the synthesis and characterization of some

hexanuclear complexes with different oxime ligands where exchange interaction

mediated through oximates (=N-O) and in some complex with a combination of oxime

and oxo bridge.

(ii) Evaluation of Coupling Constant:

The spin-Hamiltonian accounting for this isotropic exchange interactions may be

written as H = - 2 Σ Jij Si Sj, where the sum is taken over all pairwise interactions of

intensity Jij between spins Si and Sj in the molecule. This model of the isotropic

interaction between the spin carriers is based on the concept of magnetic orbitals and

overlaps densities between pairs of such orbitals, and allows an analysis of the spin

coupling. In molecular magnetism we are concerned not only with local spins associated

with metal ions, but also with molecular spins associated with open-shell molecular units

as a whole. It turns that the interaction between two such molecular units may not be of

the same nature as the interactions between the two metal ions, belonging to a molecular

unit, the other one belonging to the other molecular unit.

There are three mathematical methods for calculating the magnetic susceptibilities in

polynuclear complexes:

(a) Vector Coupling (VC)

(b) Full matrix diagonalization (FMD)

The VC method, formulated by Kambe,40 is the easiest of three to set up and of use.

It can results in the evaluation of closed form expressions for the susceptibility, which

chemists feel comfortable working with. This method limited by the symmetry of the

cluster system; since one has to be able to obtain appropriate and unique solutions to

multivariable problems, it can therefore be used only for certain symmetries. Departure

from these symmetries causes the Hamiltonian, to involve more J values, some of which

may or may not be equal.

INTRODUCTION AND OBJECTIVES

ITO or FMD methods must be then used. FMD has a major drawback in that it can result

in very large matrices requiring long diagonalization times, and thus long computing

times. The ITO method41 on the other hand reduces the size of the matrices and

computation times dramatically. Its drawback is that it is a bit more difficult to set up in

the first case and requires a considerable degree or sophisticated mathematics. It is

difficult to include single-ion effects in the ITO calculations such as zero-field splitting

(ZFS). In contrast it is relatively easy to set up a matrix in FMD and to include effects

such as ZFS.

(iii) Magnetizations at different fields:

A sample containing 1 mol of a molecular compound within an homogeneous magnetic

field H, acquires a molar magnetization M related to H through, ∂M / ∂H = χ where χ is

the molar magnetic susceptibility. When the magnetic field is weak enough, χ is

independent of H, such that one can write M = χ H. The molar magnetization M, is

expressed in cm3 G mol-1, alternatively, M may be expressed in Nß units, N being the

Avogadro's number and ß the electronic bohr magneton. The molar paramagnetic

susceptibility characterizes the way in which an applied magnetic field H interacts with

the angular momentum associated with the thermally populated states of a molecule.

When a sample is perturbed by an external magnetic field, its magnetization is related to

its energy variation through M = - ∂E / ∂H. This equation may be easily translated into

the language of quantum mechanics. The macroscopic molar magnetization M is then

obtained by a sum of the microscopic magnetizations weighted according to the

Boltzmann distribution law, which leads to,

M = [NΣn (∂En / ∂H) exp(-En / kT)] / Σn exp(-En / kT), where T is the temperature and k is

the Boltzmann constant. The above equation may be considered as a fundamental

expression in molecular magnetism. The molar magnetic susceptibility varies as C/T, the

constant C depending on the spin multiplicity of the ground state; this is the Curie law,

which was proposed in 1910 from experimental data before the introduction of quantum

mechanics and it is important to keep in mind that the Curie law is valid only when H /

kT is small enough. The molar magnetization is then linear in H. When H / kT become

large, then M must be calculated from the fundamental equation above. On the contrary,

when H / kT becomes very large, M approaches the saturation value Ms, Ms = NgßS. The

saturation magnetization will be expressed in the following chapters in Nß units; its value

is simply given by gS.

(iv) Different methods used for characterization of compounds:

CHAPTER 1

To identify or assign the organic and inorganic compounds from the synergistic

information afforded by the combination of mass (MS), infrared (IR), nuclear magnetic

resonance (NMR) and UV-VIS absorption spectrum techniques will be employed.

Essentially, the molecule is perturbed by these energy probes and the molecule's

responses are recorded as spectra.

Infrared (IR) radiation refers broadly to that part of the electromagnetic spectrum

between the visible and microwave regions. Of greatest practical use to the synthetic

chemist is interested in the region between 4000 and 400 cm-1. Although the IR spectrum

is characteristic of the entire molecule, it is true that certain groups of atoms give rise to

bands at or near the same frequency regardless of the structure of the rest of the molecule.

It is the persistence of these characteristic bands that permits the chemist to obtain useful

structural information by simple inspection and reference to general charts of

characteristic group frequencies. Since it is not possible to use IR spectra solely for

identification, a detailed analysis of the spectrum will not be required but only the

assignments of the characteristic groups present in the ligand and complexes.

Various methods of producing molecular ions (including EI and ESI method) will be

taken into consideration for the structure elucidation.

Electrochemical methods offer a unique access to information on chemical, biochemical

and physical systems. The "Electrochemical methods", contains the most frequently

utilized techniques, i.e., cyclic voltammetry, pulse and square-wave voltammetry and

coulometry etc. Among the electrochemical techniques, cyclic voltammetry is frequently

used because it offers wealth experimental information and insights into both the

thermodynamic and kinetic details of many chemical systems. So voltametric

experiments with microcrystalline particulate deposits present on the electrode surface

provide information on the redox processes at the solid/solvent electrolyte interface, so

for the insight into the redox processes these techniques will also be employed.

Mössbauer and EPR spectroscopy techniques will also be taken into consideration

occasionally for the assignment of the oxidation state of iron atoms in the complex

through Mössbauer spectroscopy and also to extract chemical information EPR

spectroscopy will also be employed.

At the same time X-ray single crystal structure also important for the information of

structural parameters that is necessary for better understanding of magnetostructural

studies.

INTRODUCTION AND OBJECTIVES

(v) Advantages of heteronuclear complexes over homometal complexes:

Both homo- and heteropolymetallic systems16 provide opportunities to understand

fundamental factors that govern exchange interactions. New exchange pathways can be

expected for heteropolynuclear complexes where unusual sets of magnetic orbitals can be

made to overlap with each other; hence investigations of a series of heteropolynuclear

complexes might be more informative in comparison to those of homopolynuclear

complexes. It is worth mentioning in this connection that the presence of different

competing interactions in polynuclear complexes may lead to ground and other low-lying

states that cannot be expected by simple combination of the local spins according to the

nature of the interactions present between the spin carriers.

Another good reason for studying polynuclear complexes is that they may be building

blocks for molecular-based magnetic materials. Although the pairwise exchange

interactions in majority of the complexes are found to be antiferromagnetic, "spin-

frustration"17-21 in a general sense of the term, or more accurately competing spin

interactions, in a polynuclear complex can result in ground states having a relatively large

number of unpaired electrons. Although spin frustration is a well known magnetic

phenomenon for extended lattices,22 its application to the magnetochemistry of discrete

polynuclear complexes is not widely recognized.23 Competing spin interactions may give

rise to unpredictable ground state spins and peculiar spin state structures. Thus the

situation of ground state degeneracy induced by competing spin interactions is worth

investigating.

"Spin frustration" will be used as a general case in certain topological arrangements of

paramagnetic centers with competing exchange interactions of comparable magnitude

preventing or frustrating the spin alignments that would otherwise be preferred in the

ground state. The ground state is particularly sensitive to the relative magnitudes of the

competing interactions and the spin of the ground state adopts an intermediate value

rather than the lowest value that might be anticipated for an antiferromagnetically

coupled system. "Spin-frustration degeneracy" of the ground state19 leading to unusual

electronic properties might be observed for some of the heteropolynuclear compounds to

be synthesized here.

Linear heterotrinuclear complexes with general formula [(Me3Tacn)MA(oxime

bridge)2-3MBMA(Me3Tacn)]2+/3+ were exclusively investigated. In these compounds the

central oxime bridge is usually formed from dimethylglyoxime units N-cordinated to

central ion MB and bridged through the oxygen atoms to the terminal ions MA. Depending

CHAPTER 1

on the metallic ions involved, these complexes exhibit both antiferromagnetic and

ferromagnetic properties. In the Cr(III) series complexes with Cu(II) and Mn(II) ions in

the central position lead to ferromagnetic couplings while Ni(II) and Fe(III) result in

antiferromagnetic exchange interactions. The Mn(III) series also exhibits alternate ferro-

and antiferromagnetic exchange interaction. The complex MnIV2Cu is isoelectronic with

CrIII2Cu and also exhibits ferromagnetic exchange interaction. The much stronger

interaction in the MnIV2CuII core can be attributed to the higher charge and consequently

higher covalent character of the bonds to the MnIV ion. In contrast to the Mn(IV) series

all the Fe(III) series exhibit antiferromagnetic exchange interaction.

Recently a rational assembly of a series of exchange coupled linear

heterotrinuclear complexes of the type MAMBMC based on a strategy using metal

oximates as building blocks has been reported.35 Thus complexes [(Me3T

acn)MA(LOX)MBMC]3+ where MA = Fe(III) and Co(III) is facially coordinated to three

nitrogen donors of the macrocyclic amine and MB = Cu(II) or Ni(II) and MC = Ni(II) or

Cu(II) are embedded in a asymmetric dicompartmental imine-oxime ligand H4LOX. The

compounds synthesized in this series MAMBMC are FeIIICuIINiII and FeIIINiIICuII. The

variable temperature magnetic moments reveal ground states of ST = 3 and 2 respectively,

also confirmed by the magnetization measurements

The magnetic interactions operating in this type of linear trinuclear complexes

result in a ground state of high spin multiplicity, although the nearest neighbor spin

alignments are antiparallel. Isoelectronic FeIIICuIINiII and FeIIINiIICuII demonstrate the

strong influence of topological features on the magnetostructural properties. Following

the Goodenough and Kanamori rules a qualitative rationalization for the exchange paths

prevailing between neighboring and terminal spin carriers in these heterotrinuclear

complexes has been presented and implies the predominance of σ-interactions over π-

interactions.

The continuous development of exchange coupled heterometallic systems

started with the aim of understanding interactions between two magnetic ions. The

number of papers cited testifies to the uninterrupted interest in this area of coordination

chemistry involving exchange coupled metal oximates. Of particular interest is the small

but significant effect of bridging ligands like carboxylate anions for cooperation with the

ancillary ligand, viz the oxime ligands to build up high nuclearity metal clusters.

To summarize, this work involves studies of magnetic properties of

complexes containing paramagnetic metal centers in different molecular topology and

INTRODUCTION AND OBJECTIVES

this thesis is devoted to the homo- and heterometallic exchange coupled polynuclear

complexes.

1.3 References:

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(2) J. B. Goodenough, "Magnetism and the Chemical Bond (Interscience, New York,

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D. Gatteschi, O. Kahn, NATO ASI Series C, Vol. 140, Reidel, Dordrecht 1985.

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CHAPTER 1

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INTRODUCTION AND OBJECTIVES

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(27) P. Chaudhuri, M. Winter, P. Fleischhauer, W. Haase, U. Flörke and H.-J. Haupt, J.

Chem. Soc., Chem. Commun., 1990, 1728.

(28) (a) E. I. Ochiai, J. Chem. Ed. 1993, 70, 128; (b) J. Z. Pedersen and A. Finazzi-Agro,

FEBS Lett. 1993, 325, 53; (c) "Metal Ions in Biologiical Systems", Eds. H. Sigel and A.

Sigel, Marcel Dekker, New York, Vol. 30, 1994; (d) M. M. Fontecave and J.-L. Pierre,

Bull. Soc. Chim. Fr. 1996, 133, 653; (e) G. T. Babcock, M. Espe, C. Hoganson, N.

Lyldakis-Simantiris, J. McCracken, W. Shi, S. Styring, C. Tommos and K. Warncke,

Acta Chem. Scand, 1997, 51, 533; (f) J. Stubbe and W. A. Van der donk, Chem. Rev.,

1998, 98, 705.

(29) V. Pavlischuk, F. Birkelbach, T. Weyhermüller, K. Wieghardt and P. Chaudhuri,

Inorg. Chem., 2002, 41, 4405

(30) P. Chaudhuri, Coord. Chem. Rev., 2003, 243, 143

(31) (a) F. Birkelbach, U. Flörke, H-J. Haupt, C. Butzlaff, A.X. Trautwein, K. Wieghardt

and P. Chaudhuri, Inorg. Chem.,1998, 37, 2000; (b) D. Burdinsky, F. Birkelbach, T.

Weyhermüller, U. Flörke, H-J. Haupt, M. Lengen, A.X. Trautwein, E. Bill, K. Wieghardt

and P.Chaudhuri, Inorg. Chem., 1998, 37,1009; (c) P. Chaudhuri, M. Winter, B. P. C. D.

Vedova, P. Fleischhauer, W. Hasse, U. Flörke and H-J. Haupt, Inorg. Chem., 1991, 30,

4777; (d) P. Chaudhuri, M. Winter, B. P. C. D. Vedova, E. Bill, A. Trautwein, S.

Gehring, P. Fleischhauer, B. Nuber and J. Weiss Inorg. Chem., 1991, 30, 2148

(32) S. Ross, T. Weyhermüller, E. Bill, K. Wieghardt and P. Chaudhuri, Inorg. Chem.,

2001, 40, 6656

(33) P. Basu, S. Pal, and A. Chakravorty. Inorg. Chem., 1988, 27, 1848

(34) S. G. Sreerama and S.Pal. Inorg. Chem., 2002, 41, 4843

(35) (a) C. N. Verani, T. Weyhermüller, E. Rentschler, E. Bill and P. Chaudhuri., J.

Chem. Soc., Chem. Commun., 1998, 2475; (b) C. N. Verani, E. Rentschler, T.

Weyhermüller, E. Bill and P. Chaudhuri, J. Chem. Soc. Dalton Trans., 2000, 4263; (c) C.

N. Verani, Dissertation, Bochum, Germany, 2000

(36) (a) C. Krebs, Dissertation, Bochum, Germany, 1997; (b) C. Krebs, M. Winter, T.

Weyhermüller, E. Bill, K. Wieghardt and P. Chaudhuri, J. Chem. Soc., Chem Commun.,

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U. Flörke, Eur. J. Inorg. Chem., 2003, 541

CHAPTER 1

(38) P. Chaudhuri, M. Hess, E. Rentschler, T. Weyhermüller and U. Flörke, New

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INTRODUCTION AND OBJECTIVES

CHAPTER 2

CHAPTER -2

TRINUCLEAR METAL OXIMATES: DESIGNED SYNTHESIS

AND MAGNETIC PROPERTIES OF LINEAR NiIIMnIIINiII,

NiIICrIIINiII AND TRIANGULAR NiII3 COMPLEXES

Ni(1)

Ni(2) Ni(3)

Py Nox Oox =PyA

2.1 Introduction:

The homo and heteropolynuclear complexes are of interest to the inorganic

chemists for their relevance to molecular magnetism (Chapter-1). This chapter describes

some 3d-transition metal homo-and heterotrinuclear complexes which are relevant to the

importance in magnetostructural studies. In an isosceles triangle how competing exchange

interaction with two different coupling constants J and J' influences in determining the

ground state will be discussed. If both the exchange coupling constants are negative, the

exact nature of the ground state depends on the ratio ρ = J' / J and how this affects is also

evidenced in the triangular NiII3 (3) complex.

A remarkable feature of the oxime ligands1 is their propensity to form polynuclear

complexes,2 both homo-and heteronuclear in which oxime function (>C=N-O) acts as a

LINEAR AND TRIANGULAR TRINUCLEAR METAL OXIMATE COMPLEXES

bridging unit to yield magnetically interesting compounds.3 This chapter describes the spin-

spin interactions between the paramagnetic metal centers through multi-atom bridges and

deals specifically with the ligation property of tris(pyridine-2-aldoximato)nickel(II),

[Ni(PyA)3]-. It was prompted to study the coordination chemistry of this metal complex as a

ligand because of the opportunity for its facile in-situ formation dictated by the

thermodynamic stability of the resulting monoanion containing facially disposed three

pendent oxime oxygen atoms for ligation.4 So the ability of [Ni(PyA)3]- monoanion will be

explored in generating such homo-and heteropolynuclear complexes which will allow us to

study exchange-coupled interactions.

2.2 Synthesis:

The reaction of Syn-2-pyridinealdoxime with NiCl2.6H2O and

Mn(ClO4)2.6H2O; with NiCl2.6H2O and Cr(ClO4)3.6H2O in 6:2:1 ratio in presence of

NBu4OMe as base yielded heterotrinuclear complexes [Ni(PyA)3Mn(PyA)3Ni] (ClO4) (1)

and [Ni(PyA)3Cr(PyA)3Ni] (ClO4) (2) respectively; whereas the reaction of Syn-2-

pyridinealdoxime with Ni(ClO4)2.6H2O in 6:3 ratio in presence of NBu4OMe as base yielded

homotrinuclear complex [Ni3(PyA)5(PyAH)] (ClO4) (3). In all the three complexes

tris(pyridine-2-aldoximato)nickel(II) unit acting as a building block for the trinuclear

complexes. These complexes will be abbreviated as NiIIMnIIINiII (1), NiIICrIIINiII (2) and

contain metal centers in linear arrangement while homotrinuclear complex as NiII3 (3) where

the three nickel(II) centers are disposed in triangular fashion.

2.3 Infrared and Mass Spectroscopy:

The relevant bands in IR spectra of comparable pyridine-2-aldoximato containing

heteronuclear CrIIIMII and FeIIIMII complexes have been reported earlier by Ross et.al,4 and

the spectra of 1-3 are also very similar. A notable feature of the NO stretching for 3 is the

sharp bands at 1130, 1125, 1031 cm-1. The presence of two different coordination modes of

the oxime group in 3 is consistent with the splitting.

Electrospray-ionaziation mass spectrometry (ESI-MS) in the positive ion mode has been

proved to be very successful in characterizing NiIICrIIINiII which shows the monopositively

charged species [M-ClO4]+ as the base peak. On the contrary the signal for [M-ClO4]+ of 3

is very weak, together with the base peak for the fragment [M-ClO4-PyA]+. The manganese

CHAPTER 2

containing complex NiIIMnIIINiII does not provide signals for unambiguous

characterization.19

2.4 Solid state Structure:

2.4.1 X-ray structure of [Ni(PyA)3Mn(PyA)3Ni] ClO4; H2O (1).

The lattice is built of discrete trinuclear monocations, perchlorate anions,

and water molecules of crystallizations. The trinuclear complex contains two [NiII(PyA3)]-

moieties-each having a NiN6 coordination sphere-acting as a tridentate ligand through the

pendent oximato oxygen atoms to the centrally placed manganese (III) ion. A view of the

cation [Mn(PyA)6Ni2]+ ion in complex 1 is shown in Figure 2.1. Selected bond distances

and angles are listed in Table2.1. The cation [Mn(PyA)6Ni2]+ having a crystallographic

threefold inversion symmetry has therefore a strictly linear arrangement of the NiIIMnIIINiII

array and the two [Ni(PyA)3]- units necessarily have opposite chirality (∆, Λ) making

[Mn(PyA6)Ni2]+ achiral.

The terminal nickel centers are six-fold coordinated yielding an NiN6 core; coordination

occurs facially through three pyridine nitrogen atoms Npy(1) and three azomethine nitrogen

atoms Nox(8), from the pyridine 2-aldoximate ligands. The Ni(1)-Nox(8) bond length

2.039(2) Å, is shorter than the Ni(1)-NPy(1), 2.107(2) Å, bond distance, as has been observed

earlier for comparable complexes.4 The Ni-N bond lengths fall within the ranges that are

considered as normal covalent bonds for high spin d8 Ni(II) ions. The facial disposition of

the three NpyNox-chelate rings at each nickel atom is necessary for the ligation of the pendant

oxime oxygen atom, O(9) and its equivalents, to the central manganese. The chelate rings

are planar. The average chelate bite angle on the two nickel centers is 86.5°. This small but

negative deviation of the bite angle from 90° necessarily implies the presence of substantial

trigonal distortion. Indeed the two nickel centers can be considered to have distorted trigonal

antiprismatic coordination, as is evident from the average twist angle Ψ of 38.0°, which

deviates appreciably from the ideal 60° for an octahedron. The trigonal twist angle Ψ is

defined as the angle between the triangular faces comprising three pyridine nitrogens, N(1)

an its equivalents and three azomethine nitrogens N(8) and its equivalents. That the array

Ni(N-O)Mn is not planar is shown by the dihedral angle θ of 36.5° between the planes

comprising Mn(O-N) and Ni(N-O) atoms. These distortion of the 6 coordinate d8 Ni(II) ion

in complex 1 can be ascribed to both electronic LFSE and its size effects, as has been

discussed earlier.4-6

LINEAR AND TRIANGULAR TRINUCLEAR METAL OXIMATE COMPLEXES

The central manganese atom Mn(1) is surrounded by an almost perfect octahedron

(deviation being less than 4°) of six oximato oxygen atoms O(9), pendent from the two [Ni

(PyA)3]- fragments. All angles at the metal between cis oxygen atoms deviate from ideal

90°, being 86.20(5)° and 93.80(5)°, the cis Mn(1)-O bond angle of 93.8(5)° represents the

oxygen atoms originated from the same [Ni(PyA)3]- fragment, where as the angle 86.20(5)°

is exhibited between the oxygens of two different [Ni(PyA)3]- fragments. The Mn(1)-O(9)

distance of 2.027(1) Å is significantly shorter than the divalent manganese–oxygen distances

lying in the range 2.101(4)-2.218(2) Å,7 indicating that Mn(1) is in higher oxidation state

than +II. That the central manganese ion must be ascribed to a +III (d4 high spin) oxidation

level is borne out by the facts that:(i) a perchlorate anion is present for maintaining the

electroneutrality of the monocationic [Mn(PyA6)Ni2]+ complex, (ii) the magnetic data can

only be simulated by considering an SMn = 2.0 for the central Mn(1) center, and, (iii) the

complex is X-band EPR silent at 4-20K.

Figure 2.1: ORTEP and labeling scheme for NiIIMnIIINiII (1)

There are rare structural data on high spin Mn(III) complexes with six identical

monodentate ligands,8 although a large number of tris(bidentate) and polydentate chelate

complexes are known.7 The Mn(1)-O(9) distance of 2.027(1) Å, found in complex 1 is

completely in conformity with the Mn(III)-O distances observed in the comparable

unambiguously established Mn(III)-complexes including the complexes with the Mn(III)-

Ooxime bonds.9-10 The cation in 1 has crystallographic site symmetry 3, (three fold inversion

CHAPTER 2

symmetry)-which requires the six Mn-O bonds to be equivalent and hence the Jahn-Tellar

distortion expected for a high spin d4 Mn(III) is not observed for the octahedral Mn(1)O6

polyhedron. The most reasonable explanation for the equivalence of the Mn-O bond lengths

lies presumably in the dynamic Jahn-Tellar effect. It is concluded, complex 1 contains a

NiII2MnIII (high spin) core. Very similar oximato-bridged trinuclear MFe2(low spin) have

also been reported, although from the magnetochemical point of view they are mononuclear

with central paramagnetic metal ions.11

Table 2.1: Selected Bond Lengths (Å) and Angles (deg) [Ni(PyA)3Mn(PyA)3Ni] ClO4; H2O (1).

Ni(1)•••Mn(1) 3.57 Ni(1)•••Ni(1A) 7.14

Ni(1)-N(8)#1 2.039(15) Mn(1)-O(9)

2.027(14)#3

Ni(1)-N(8) 2.039(15) Mn(1)-O(9)

2.027(14)#4

Ni(1)-N(8)#2 2.039(15) Mn(1)-O(9)

2.027(14)#5

Ni(1)-N(1) 2.017(15) Mn(1)-O(9) 2.027(14)

Ni(1)-N(1)#1 2.017(15) Mn(1)-O(9)

2.027(14)#1

Ni(1)-N(1)#2 2.017(15) Mn(1)-O(9)

2.027(14)#2

2.4.2 X-ray structure of [Ni(PyA)3Cr(PyA)3Ni](ClO4) (2).

The heterotrinuclear complex, 2, NiIICrIIINiII also crystallizes like complex 1 in the space

group R-3, with threefold inversion symmetry and is isostructural as expected with complex

1. The trinuclear complex consists of two [NiII(PyA)3]- moieties-each having a NiN6

coordination sphere acting as tridentate ligand through the pendent oximato oxygen atoms to

the centrally placed Cr(III) ion. A view of the cation [Cr(PyA)6Ni2]+ in complex 2 is shown

in Figure 2.2. The terminal [Ni(PyA)3]- is very similar to that described for complex 1.

The central chromium atom Cr(1) is surrounded by an almost perfect octahedron of six

oximato oxygen atoms, O(9) and its equivalents, pendants from the terminal two [Ni(PyA)3]-

-fragments. The site symmetry 3¯ in the cation of 2 yields the six Cr(1)-O bonds to be

equivalent for the octahedral Cr(1)-O6 polyhedron. The Cr(1)-O(9) distance of 1.994(1) Å,

found in complex 2 is completely in conformity with the Cr(III)-O observed in the

comparable Cr(III)-complexes. That complex 2 is monocationic containing the NiIICrIIINiII

ions is also evidenced by the presence of an anion perchlorate and the magnetic data

described later. Selected bond distances and angles are listed in Table 2.2.

LINEAR AND TRIANGULAR TRINUCLEAR METAL OXIMATE COMPLEXES

Figure 2.2: ORTEP and labeling scheme for NiIICrIIINiII (2)

Table 2.2: Selected Bond Lengths (Å) and Angles (deg) [Ni(PyA)3Cr(PyA)3Ni] ClO4; H2O (2).

Ni(1)•••Cr(1) 3.552 Ni(1)•••Ni(1A) 7.104

Ni(1)-N(8)#1 2.036(13) Cr(1)-O(9)

1.9936(11)#1

Ni(1)-N(8)#3 2.036(13) Cr(1)-O(9)

1.9936(11)#2

Ni(1)-N(8) 2.036(13) Cr(1)-O(9) 1.9936(11)#3

Ni(1)-N(1)#1 2.108(13) Cr(1)-O(9)

1.9936(11)#4

Ni(1)-N(1) 2.108(13) Cr(1)-O(9) 1.9937(11)#5

Ni(1)-N(1)#3 2.108(13) Cr(1)-O(9) 1.9937(11)

2.4.3 X-ray structure of [Ni3 (PyA)5(PyAH)] CIO4 •CH3CN (3).

The molecular geometry and atom-labeling scheme of the molecule has been shown in

Figure 2.3. The structure of the complex consists of discrete trinuclear monocations

[Ni3(PyA)5(PyAH)]+, perchlorate anions, and acetonitrile molecules. There are three types of

oximic groups: (i) two non-bridging >C= N-OH groups, O(39) and O(59) of which a proton

is disordered over both sites, which is virtually the universal bonding mode for oximes, (ii) a

two atom (N-O) bridging group, N(8)O(9) and N(18)O(19), as found in preponderance over

CHAPTER 2

(iii), (iii) a monoatomic oximato µ2-O bridging, O(29) and O(49). That an oxime group acts

as a bridging µ3-ligand, -N-O, is not unprecedented.14 Accordingly, the N-O bond lengths in

the oximate fragments are in the ranges 1.332(2), 1.341(2)-1.359(2) and 1.370(2)-1.373(2) Å

and correspond well with those observed in the comparable structures. The bond distance

C=Nox at average 1.291 ± 0.011 Å and the bridging bond angle C=Nox-O of average

118.7±1° and non-bridging C=Nox-O of 114.5 ± 0.2° fall in the range reported for complexes

containing pyridine-2-aldoximato as ligands.4,10,18 All other intraligand bond parameters are

unexceptional. Figure 2.4 highlights not only the coordination spheres of the three nickel

atoms, but also illustrates the three different coordination modes of pyridine-2-aldoximato(-)

ion, NpyNox-O, in complex 3. The three nickel atoms form a triangular arrangements with the

separations of Ni(1)..Ni(2) 3.240, Ni(1)…Ni(3) 3.276 and Ni(2)…Ni(3) 3.951 Å.

The nickel ions all display pseudo-octahedral geometry with NiN4O2 coordination

spheres. Ni(1) is coordinated to cis-(Npy)2, tarns-(Nox)2 and cis-(µ2-Oox)2 donor atoms, where

Npy, Nox, Oox represent respectively pyridine nitrogen, oxime nitrogen and monoatomic

bridging oxime oxygen. The two bridging ligands between Ni(1) and Ni(2) are the

monoatomic µ2-O(49)(which is bonded to N(48) of an oxime group), N(8)O(9). The

bridging connectivities between Ni(1) and Ni(3) are also very similar with µ2-O(29) and

N(18)O(19). On the contrary Ni(2) and Ni(3) are bridged through only the two µ2-O-

oxygens, O(49) and O(49). The coordination octahedron of Ni(1) is slightly irregular, with

several angles departing from right angles by 11° or so, as exemplified in Figure 2.3 by

N(8)-Ni(1)-N(11) at 101.54(6)°. The distortion from octahedral geometry for Ni(2) and

Ni(3) is more pronounced; the trans donor angles deviate from 180° by nearly 20°, viz.

N(41)-Ni(3)-O(29) at 161.59(5)° and N(21)-Ni(2)-O(49) at 162.79(5)°. Selected bond

lengths and angles are given in Table 2.3. The Ni(1)-Nox bond lengths are shorter than the

Ni(1)-Npy bond lengths, while for Ni(2) and Ni(3), the reverse is true. As expected the Ni-

µ2-Oox bond lengths are significantly longer than the Ni-Oox bond lengths involving the two

atomic oximato bridges, e.g. Ni(3)-O(29) 2.116(1) Å vs. Ni(3)-O(19) 2.051(1) Å. The Ni-N

and Ni-O bond distances are consistent with normal covalent bonds for high spin d8 Ni(II)

ions with oximato ligands.

LINEAR AND TRIANGULAR TRINUCLEAR METAL OXIMATE COMPLEXES

Figure 2.3: ORTEP and labeling scheme for NiII

(3)

The short O(39)....O(59) separation of 2.414(2) Å clearly indicates the occurrence of

strong hydrogen bond interactions between these oxygen atoms, suggesting protonated

uncoordinated O(59) and O(39). Indeed, a difference Fourier in the later refinement stages

did reveal a peak assignable to a proton, appearing between O(39) and O(59) and it was

included in this position in the final refinement cycle (occupation factor 0.5 each). The

presence of a single proton per trinuclear unit with six pyridine–2-aldoximato anions is in

complete accord with the charge balance considerations of the monocations in complex 3.

The oxime hydrogen was refined isotropically, and approximate bond distances within the

symmetrical hydrogen bridge are about 0.9Å; O(39)-H = 0.898 and H....O(59)=0.905 Å. That

the hydrogen bonding is symmetrical is also manifested in similar N-O lengths: O (39)-N

(38) = 1.359(2) and O(59)-N(58)=1.341(2) Å.

CHAPTER 2

Ni(1)

Ni(2) Ni(3)

=PyA

Figure 2.4: A schematic representation of the atom connectivities in the triangular trinickel(II) present

in the cation of complex 3 to highlight three different coordination modes of pyridine-2-aldoximato

monoanion, NpyNox-

Table 2.3: Selected Bond Lengths (Å) and Angles (deg) [Ni3 (PyA)5(PyAH)] CIO4 •CH3CN (3).

Ni(1)•••Ni(2) 3.240 Ni(1)•••Ni(3) 3.276

Ni(2)•••Ni(3) 3.951

Ni(1)-N(18) 2.017(14) Ni(3)-N(51) 2.071(15)

Ni(1)-N(8) 2.024(14) Ni(3)-N(41) 2.072(15)

Ni(1)-N(11) 2.104(14) Ni(3)-N(48) 2.081(14)

Ni(1)-N(1) 2.117(14) Ni(3)-N(58) 2.164(2)

Ni(1)-O(49) 2.104(12) Ni(3)-O(19) 2.051(12)

Ni(1)-O(29) 2.138(12) Ni(3)-O(29) 2.116(12)

Ni(2)-N(28) 2.069(14) Ni(3)-O(29)-Ni(1) 100.7(5)

Ni(2)-N(31) 2.070(15) Ni(31)-O(49)-Ni(2) 100.6(5)

Ni(2)-N(21) 2.080(134

LINEAR AND TRIANGULAR TRINUCLEAR METAL OXIMATE COMPLEXES

Ni(2)-N(38) 2.123(2)

Ni(2)-O(49) 2.107(12)

Ni(2)-O(9) 2.042(13)

2.5 Magnetic Properties:

Magnetic susceptibility data for polycrystalline samples of the complexes were collected

in the temperature range 2-290 K in an applied magnetic field of 1T. We use the Heisenberg

spin Hamiltanonian in the form: H= - 2J(S1S2+S2S3)-2J13(S1S3) , for an isotropic exchange

coupling with S1 = S3 = SNi = 1 and S2 = SMn = 2 for 1, S1 = S3 = SNi = 1 and S2 = SCr = 3/2

for 2. The experimental data as the effective magnetic moments µeff versus temperature T.

are displayed in Figures 2.5 and 2.6. The experimental magnetic data were simulated using a

least squares fitting computer program with a full matrix diagonalization approach and the

solid lines in Figures 2.5 and 2.6 represent the simulations. Table 2.4 summarizes intratrimer

magnetic parameters.

The magnetic moment µeff/molecule for 1, NiIIMnIIINiII, of 6.13 µB (χM•T = 4.692

cm3.K.mol-1) decreases monotonically with decreasing temperature until it reaches a value

of 5.199 µB (χM•T = 3.38 cm3.K.mol-1) at 50 K and then starts to decrease further but rapidly

and reaches a value of 1.639 µB (χM•T = 0.336 cm3.K.mol-1) at 2 K. This temperature

dependence is in agreement with the weak antiferromagnetic coupling between the

neighboring Ni(II) and Mn(III) ions resulting in a diamagnetic ST = 0 ground state for 1. A

simulation kept J13 = 0 and shown as a solid line in Figure 2.4 results in J = - 3.18cm-1, gNi =

2.05, gMn = 1.97 and 2% paramagnetic impurity with S = 2.0. The observed

antiferromagnetic coupling agrees well with the comparable exchange coupling constants

reported earlier.9-10

The variable-temperature magnetic movements µeff vs. T-plot for complex 2,

NiIICrIIINiII also shown in Figure 2.6 exhibits in the region 293-100 K nearly temperature-

independent µeff value of 5.52µB (χM•T = 3.816 cm3.K.mol-1), which is very close to the

value expected for three uncoupled spins for S1 = S3 = 1.0 and S2 = 3/2 (µeff = 5.56 µB with g

= 2.0). Below 100 K the µeff values increase very slowly to reach a peak value of 5.733µB

(χM•T = 4.11 cm3.K.mol-1) at 10 K. The increase in µeff values indicates an overall

ferromagnetic coupling. A simulation shown as a solid line in Figure 2.6 results in J = J12 =

J23 = + 0.60 cm-1, J13 = - 0.90cm-1, gNi = g1 = g3 = 2.0(fixed) and gCr = g2 = 1.95 (fixed).

CHAPTER 2

50 100 150 200 250 300

µeff / µB

T/K

Figure 2.5: Magnetic data for NiIIMnIIINiII (1) and NiII

3 (3) plot of µeff vs. T. The bold points represent

the experimental data while the solid line represents the simulation.

Ni2

Ni1 Mn1

Ni2

Ni1 Cr1

Scheme 1: Representation of the magnetic exchange coupling model.

LINEAR AND TRIANGULAR TRINUCLEAR METAL OXIMATE COMPLEXES

The energy ladder of the spin-states shows that two states with ST = 7/2 and 3/2 form the

ground state, which is only 1.8 cm-1 below the first excited state with an another ST = 7/2.

The observed ferromagnetic coupling between Cr(III) and Ni(II) centers agrees well with the

comparable exchange couplings reported in the literature and is in accord with the

Goodenough-Kanamori orthogonality rule3a as expressed by the Ginsberg’s symbols: eg(Ni)

⎜⎜σNO ⊥ t2g(Cr)6,16

50 100 150 200 250 300

5.0

5.2

5.4

5.6

5.8

6.0

µeff/µB

T/K

Figure 2.6: Magnetic data for NiIICrIIINiII (2) plot of µeff vs. T. The bold points represent the experimental

data while the solid line represents the simulation.

The magnetic movement µeff vs. T plot with an applied field of 1 T for 3 in the range 2-

290 K is shown in Figure 2.4. The magnetic movement µeff /molecule for 3, NiII3, of 4.896

µB (χM•T = 2.998 cm3.K.mol-1), at 290 K decreases monotonically with the decreasing

temperature until it reaches a value of 2.790 µB (χM•T = 0.9735 cm3.K.mol-1) at 5 K, which

then drops to 2.535 µB (χM•T = 0.8036 cm3.K.mol-1) at 2 K. This temperature dependence is

in agreement with an antiferromagnetic coupling between the Ni(II) ions resulting in triplet

ST = 1 ground state for 3.

On the basis of crystal structure of 3, NiII3 triangular unit with the

[Ni3(PyA)5(PyAH)]+ can be considered as scalene as a Ni(1)...Ni(2) (3.240 Å), Ni(1)...Ni(3)

(3.276 Å) and Ni(2)...Ni(3) (3.951 Å) distances are different. Hence three pair wise exchange

interactions with J12, J13 and J23 at the beginning were used to simulate the experimental

magnetic data. A good fit (not shown) was obtained with the fitting parameter: J12 = - 32.7

cm-1, J13 = + 12.5 cm-1, J23 = + 25.0 cm-1, g1 = g2 = g3= 2.0. As a coupling constant appear to

CHAPTER 2

us to be physically unreasonable, we generated plots of the relative error for the fitting of the

data as a function of “J” and g, which show clearly the strong correlation and local minimum

nature of the fitting. Hence, the data for complex 3 were analyzed as an isosceles system

with the “two–J” model; a similar magnetochemical analysis of another triangular oxime

bridged NiII3 complex is known in the literature.14e Additionally, the bridging ligands

between Ni(1) and Ni(2) or Ni(3) are same, while Ni(2) and Ni(3) are bridged through only

two monoatomic µ2-Oox groups, which are consistent with a “two-J” model with the J = J12 =

J13 and J = J23 expected for an isosceles triangle. Thus, the spin Hamiltonian in used to

describe the isotropic exchange interaction is given by; H = - 2J(S1S2 + S1S3) - 2J'(S2S3),

where the subscripts refer to the Nickel centers labeling scheme in Figure 2.4 with S = 1.0.

An excellent fit of the experimental µeff vs. T data, shown as a solid line in Figure 2.5, with

fitting parameters J = - 8.20 ± 0.20 cm-1, J = - 2.0 ± 0.1 cm-1 and g1 = g2 = g3 = 2.07, are

obtained. No other terms were used for the simulation shown in Figure 2.5. thus, the ground

state is a triplet with ⎢ST, S*> = ⎜1,2> above which the excited states, in order of increasing

energy are, ⎜0,1>, ⎜1,1> , ⎜2,2> , ⎜1,0> , ⎜2,1> and ⎜3,2> with the first excited state ⎜0,1>

only 8.4 cm-1 and the second excited state ⎜1,1> 24.8 cm-1 above the ⎜1,2> ground state.

Such antiferromagnetic interactions in triangular NiII3 complexes are not unprecedented.10

For an isosceles triangle of three spins of S = 1.0 the two antiferromagnetic exchange

interactions J and J' compete with each other to determine the spin state energies as it is not

possible for three spins to be aligned anti parallel to each other and thus the spin state

energies become a function of the relative magnitudes of J and J', i.e., the J' / J. Ginsberg

et.al.13 have in a seminal paper pointed out for three S = 1.0 spin centers that if x = J' / J be

less than 0.5 or greater than 2.0, the ground state is a triplet, ST = 1.0. On the other hand, for

0.5 < x < 2 the ground state is ⎜0,1>. The evaluated x (= J' / J) of 0.24 for 3 is in accord with

the observed triplet ground state. We are aware of one very similar oxime bridged trinuclear

NiII3 complex17e in which the ratio of the evaluated exchange coupling constants was found

to be x = J' / J = 0.53 for which hence a ground state of ⎜0,1> is expected.

LINEAR AND TRIANGULAR TRINUCLEAR METAL OXIMATE COMPLEXES

Table 2.4: Intratrimer magnetic parameters for homo-and heterotrinuclear complexes 1-3

Compounds Magnetic core J12 [cm-1] J13[cm-1] J23[cm-1] gNi gMn gCr

1 NiIIMnIIINiII J12 = J23 - 3.18 2.05 1.97

2 NiIICrIIINiII J12 = J23 + 0.6 - 0.9 2.00 1.95

3 NiII3J12 = J13 - 8.2 ± 0.2 -2.0 ± 0.1 2.07

The evaluated exchange coupling constant J of - 8.2 cm –1 for 3 along the short

edges Ni(1)/Ni(2) and Ni(1)/Ni(3), of the isosceles Ni(II) triangle does fall in the lower end

of the range which has been observed for oximate bridge-Ni(II) complexes1a. This moderate

coupling is consistent with its mediation by two types of oximate bridge, a single atom µ3-O

bridge and a two-atom N-O linkage, of which the later is expected to provide the main

super-exchange σ-pathway along the short-edges of the triangle. A single-atom oximate µ3-

O bridges directly Ni(1) to each of Ni(2) and Ni(3) (O(49) and O(29), respectively) and thus

increases the Ni(2)-µ3-O (49) and Ni(3)-µ3-O (29) bond lengths in comparison to those for

oximate µ2-O(O(9) and O(19)) and hence a diminution of the strength of antiferromagnetic

exchange coupling is observed in a manner similar to protonation and metalaton of the µ2-

oxo bridge.14 Additionally, a two-atom N-O-bridge along the short edges of the triangle

links Ni(1) to Ni(2) and Ni(3) contributing mostly to the net coupling. Thus, the very weak

coupling J' of – 2 cm-1 transmitted along the long edge of the Ni(II)-triangle is attributed to

the µ3-O nature of the oximate -O, O(49) and O(29).

It is pertinent at this point to mention that in a dinickel(II) complex containing only

three two-atom N-O linkages, [LNi(PyA)3Ni]+ were L represents a tridentate amine 1,4,7-

trimethyl-1,4,7-triazacyclononane, the J-value has been found to be – 32 cm-1.15

By considering that in complex 3 there is only one, two-atom N-O bridge between

Ni(1) and Ni(2) or Ni(3), the evaluated J-value of – 8.20cm-1 is in well accord with the

expected value. The J and the J'-values for 3, - 8.2 and - 2.0 cm-1 respectively, are similar

than those in only other triangular Ni(II)-oximate complex,17e for which the corresponding

coupling constants are - 14.4 and - 7.6 cm-1. The significantly longer Ni-O bonds in complex

3 might account mostly for the weaker coupling in 3. It must be pointed out that in the limit

of weak interactions the exchange coupling constant is also sensitive to small angular

changes or distortions, but to a lesser degree.

Exchange coupling parameters reported for NiIINiII, NiIIMnIII and NiIICrIII

complexes mediated through oximate (NO) ligands are summarized in the following Table

2.5.

CHAPTER 2

Table 2.5: Magnetic parameters for exchange coupled oximate complexes

Compounds Magnetic

core

JNi(II)...Cr(III)

[cm-1]

JNi(II)...Ni(II)

[cm-1]

JNi(II)...Mn(III)

[cm-1]

gMn(III) gNi(II) gCr(III) Ref:

[{Ni(Dien)}2(µ3-

OH)2{Ni2(Moda)4}] (ClO4)2

NiIINiII - 20.6

2.32 20b

[Ni3(Dtox)(Dtox H)2] (ClO4)2NiIINiII - 14.4 ± 0.6

- 7.6 ± 1.1

2.17 17e

[Ni4(MeOH)2(pko)6](OH)(ClO4) NiIINiII - 24.1

- 7.25

2.2 20a

[Ni4(LH)3](ClO4)2NiIINiII - 13.4 2.00 17i

K4[Ni(H2O)6][Ni8(HL)10(H2L)2] NiIINiII - 30.0 2.27 20e

[(Me3Tacn)Ni2(PyA)3](ClO4) NiIINiII - 33.6 2.16 15

[(Me3Tacn)Mn{(dmg)3Ni}

Mn(Me3Tacn)](ClO4)2

NiIIMnIII - 5.3 1.98 1.98 9

[Mn(5-R-saltmen)Ni(PyA)(bpy)2]

(ClO4)4

NiIIMnIII - 16.35 2.04 2.04 20c

[(Me3Tacn)MnNi(PyA)3]

(ClO4)

NiIIMnIII - 9.9

-14.7

1.99 2.17 15

20d

[Mn2(saltmen)Ni(PyA)2(py)2]

(ClO4)2

NiIIMnIII

[(Me3Tacn)CrNi(PyA)3]

(ClO4)2

NiIICrIII - 9.2 2.19 2.00 4b

[(Me3Tacn)CrNi{P(PyA)}3]

(ClO4)2

NiIICrIII 0 2.16 1.98 4b

[(Me3Tacn)Cr{(dmg)3Ni}Cr

(Me3Tacn)](ClO4)2

NiIICrIII - 0.7 2.19 2.00 6

2.6 References:

(1) (a) P. Chaudhuri, Coord. Chem. Rev., 2003, 243, 143; (b)A. Chakravorty, Coord.

Chem. Rev., 1974, 13, 1; (c) M. E. Keeney, K. Osseo-Ascrae and K. A. Woode.

Coord. Chem. Rev., 1984, 59, 14 ; (d) V. Y. Kukushkin and A. J. L. Pombeiro, Coord.

Chem. Rev., 1999, 181, 147; (e) A. G. Smith, P. A. Tasker and D. J. White, Coord.

Chem. Rev., 2003, 241, 61

(2) (a) R. Beckett, R. Colton, B. F. Hoskins, R. L. Martin and D. J. Vince, Aus. J.

Chem., 1969, 22, 2257; (b)D. Dutta and A. Chakravorty, Inorg. Chem., 1983, 22,

1611; (c) P. Basu, S. Pal and A. Chakravorty, Inorg. Chem., 1988, 27, 1850; (d) S.

Ganguly, S. Karmakar, C. K. Pal and A. Chakravorty, Inorg. Chem., 1999, 38, 5984;

LINEAR AND TRIANGULAR TRINUCLEAR METAL OXIMATE COMPLEXES

(e) H. Okawa, M. Koikawa, S. Kida, D. Luneau and H. Oshio, J. Chem. Soc. Dalton

Trans., 1990, 469; (f) D. Luneau, H. Oshio, H. Okawa and S. Kida, J. Chem. Soc.

Dalton Trans., 1990, 2282; (g) N. Kukita, M. Ohba, T. Shig, H. Okawa and Y. Ajiro,

J. Chem. Soc. Dalton Trans., 2001, 64; (h) Y. Agnus, R. Louis, B. Metz, C. Boudin, J.

P. Gisselbrecht and M. Gross, Inorg. Chem., 1991, 30, 3155; (i) R. Ruiz, M. Julve, J.

Faus, F. Lloret, C. M. Munoz, Y. Journaoux and C. Bois, Inorg. Chem., 1997, 36,

3434; (j) D. Blaack, A. J. Blake, K. P. Dancey, A. Harrison, M. Mcpartlin, S. Parsons,

P. A. Tasker, G. Whittaker and M. Schröder, J. Chem. Soc. Dalton Trans., 1998, 395;

(k) P. Chaudhuri, M. Winter, P. Fleischhauer, W. Haase, U. Flörke, H.-J. Haupt, J.

Chem. Soc., Chem. Commun. 1990, 1728; (l) P. Chaudhuri, M. Winter, B. P. C. D.

Vedova, P. Fleischhauer, W. Hasse, U. Flörke, H-J. Haupt, Inorg. Chem., 1991, 30,

4777; (m) D. Burdinsky, E. Bill, F. Birkelbach, K. Wieghardt and P.Chaudhuri, Inorg.

Chem., 2001, 40, 1160; (n) F. Birkelbach, M. Winter, U. Flörke, H-J. Haupt, C.

Butzlaff, M. Lengen, E. Bill, A. X. Trautwein, K. Wieghardt and P.Chaudhuri, Inorg.

Chem., 1994, 33, 3990; (o) C. Krebs, M. Winter, T. Weyhermüller, E. Bill, K.

Wieghardt and P. Chaudhuri. J. Chem.Soc., Chem Commun. 1995, 1913; (p) C. N.

Verani, E. Rentschler, T. Weyhermüller, E. Bill and P. Chaudhuri, J. Chem. Soc.

Dalton Trans 2000, 4263; (q) C. N. Verani, T. Weyhermüller, E. Rentschler, E. Bill

and P. Chaudhuri, J. Chem. Soc., Chem. Commun 1998, 2475

(3) (a) O. Kahn, "Molecular Magnetism", VCH Weinheim, 1993; (b) Molecular

Magnetism : New Magnetic Materials, ed. K. Itoh, M. Kinoshita, Gordon & Breach,

Amstardam, The Netherlands, 2000; (c) G. Christou, D. Gatteschi, D. N.

Hendrickson and R. Sessoli, MRS Bull. 2000, 25, 66; (d) D. Gatteschi and R. Sessoli,

Angew. Chem. Int. Ed., 2003, 42, 268

(4) (a) S. Ross, T. Weyhermüller, E. Bill, E. Bothe, U. Flörke, K. Wieghardt and P.

Chaudhuri, Eur.J.Inorg.Chem, 2004, 984; (b) S. Ross, T. Weyhermüller, E. Bill, K.

Wieghardt and P. Chaudhuri, Inorg. Chem., 2001, 40, 6656

(5) (a) R. A. D. Wentworth, Coord. Chem. Rev., 1972/73, 9, 171; (b) R. M. Kirchner,

C. Meali, M. Bailey, N. Howe, L. P. Torre, L. J. Wilson, L.C. Andrews, N. J. Rose and

E. C. Lingafelter, Coord. Chem. Rev., 1987, 77, 89; (c) S. A. Kunow; K. J. Takeuchi,

J. J. Grzybowski, A. J. Tireitano and V. L. Goedken, Inorg.Chim. Acta, 1996, 241, 12

(6) D. Burdinsky, F. Birkelbach, T. Weyhermüller, U. Flörke, H-J. Haupt, M. Lengen,

A. X. Trautwein, E. Bill, K. Wieghardt and P.Chaudhuri, Inorg. Chem., 1998, 37,

1009

CHAPTER 2

(7) "Comprehensive Coordination Chemistry", Ed. G. Wilkinson, Pergamon, England

1987, Vol. 4

(8) H. Aghalbozorg, G. J. Palenik, R. C. Stoufer and J. Summers, Inorg. Chem., 1982,

21, 3903

(9) F. Birkelbach, U. Flörke, H-J. Haupt, C. Butzlaff, A. X. Trautwein, K. Wieghardt

and P. Chaudhuri, Inorg. Chem., 1998, 37, 2000

(10) (a) S. G. Sreerama and S.Pal, Inorg. Chem., 2002, 41, 4843 ; (b) R. Clerac, H.

Miyasaka, M. Yamashita and C. Coulon, J. Am. Chem. Soc., 2002, 124, 12837; (c) H.

Miyasaka, R. Clerac, K. Mijushima, K. Sugiura, M. Yamashita, W. Wernsdorfer and

C. Coulon, Inorg. Chem., 2003, 42, 8203; (d) C. J. Milios, E. Kefalloniti, C. P.

Raptopoulou, A. Terzis, A. Escuer, R. Vincente and S. P. Perleples, Polyhedron, 2004,

23, 83

(11) (a) S. Pal, T. Melton, R. Mukherjee, A. R. Chakravorty, M. Tomas, L. R. Falvello

and A. Chakravorty, Inorg. Chem.,1985, 24, 1250; (b) S. Pal, R. Mukherjee, M.

Tomas, L. R. Falvello and A. Chakravorty, Inorg. Chem., 1986, 25, 200; (c) V.

Manivannan, S. Dutta, P. Basu and A. Chakravorty, Inorg. Chem., 1993, 32, 4807

(12) (a) A. Escuer, R. Vincente, S. B. Kumar, X. Solans, M. Font-Bardia and A.

Caneschi, Inorg. Chem., 1996, 35, 3094; (b) A. Escuer, I. Castro, F. Mautner, M. S. El

Fallah and R. Vincente, Inorg. Chem., 1997, 36, 4633

(13) A. P. Ginsberg, R. L. Martin and R. C. Sherwood, Inorg. Chem., 1968, 7, 392

(14) S. M. Gorun and S. J. Lippard, Inorg. Chem., 1991, 30, 1625

(15) P. Chaudhuri and T. Weyhermüller, unpublished results.

(16) A. P. Ginsberg, Inorg. Chim. Acta Rev.,1971, 5, 45

(17) Selected Examples: (a) M. S. Ma, R. J. Anjelici, D. Powell and R. A. Jacobson,

Inorg. Chem., 1980, 19, 3121; (b) P. Gouzeth, P. Jeanin, C. Rocchiaccioli-Deltcheff

and F. Valentini, J. Coord. Chem., 1979, 9, 221; (c) R. Ruiz, J. Sanz, F. Lloret, M.

Julve, J. Faus, C. Bois and M. Carmen-Munoz, J. Chem. Soc. Dalton. Trans., 1993,

3035; (d) E. Colacio, J. M. Dominguez-Vera, A. Escuer, R. Kivekas and A. Romerosa,

Inorg. Chem., 1994, 33, 3914; (e) V. V. Pavlischulk, S. V. Kolotilov, A. W. Addison,

M. J. Prushan, R. J. Butcher and L. K. Thompson, Inorg. Chem., 1999, 38, 1759; (f) P.

Chaudhuri, M. Hess, E. Rentschler, T. Weyhermüller and U. Flörke, New. J. Chem.,

1998, 22, 553; (g) H. Miyasaka, T. Nezu, F. Iwahori, S. Furukawa, K. Sugimoto, R.

Clerac, K. Sugiura and M. Yamashita, Inorg. Chem., 2003, 42, 4501; (h) Y. B. Jiang,

H. Z. Kou, R-J. Wang, A. L. Cui and J. Ribas, Inorg. Chem. 2005, 44, 709; (i) V.

LINEAR AND TRIANGULAR TRINUCLEAR METAL OXIMATE COMPLEXES

Pavlischuk, F. Birkelbach, T. Weyhermüller, K.Wieghardt and P. Chaudhuri. Inorg.

Chem., 2002, 41, 4405

(18) (a) M. Orama, H. Saarinen and J. Korvenranta, Acta Chem. Scand.Ser.A, 1989,

43, 717; (b) H. Saarinen and M. Orama, Acta Chem. Scand., 1998, 52, 1209

(19) P. Chaudhuri, E. Rentschler, F. Birkelbach, C. Krebs, E. Bill, T. Weyhermüller

and U. Flörke, Eur. J. Inorg. Chem., 2003, 541

(20) (a) M. Alexiou, C. Dendrinou-Samara, C. P. Raptopoulou, A. Terzis, V.

Tangoulis and D. P. Kessisoglou, Eur. J. Inorg. Chem., 2004, 3822; (b) V. V.

Pavlischuk, S. V. Kolotilov, A. W. Addison, M. J. Prushan, D. Schollmeyer, L. K.

Thompson and E. A. Goreshnik, Angew. Chem. Int. Ed., 2001, 40, 4734; (c) H.

Miyasaka, T. Nezu, K. Sugimoto, K-i. Sugiura, M. Yamashita and R. Clerac, Inorg.

Chem. 2004, 43, 5486; (d) R. Clerac, H. Miyasaka, M. Yamashita, and C. Coulon, J.

Am. Chem. Soc., 2002, 124, 12837; (e) J. Fans, F. Lloret, M. Julve, J. M. Clemate-

Juan, M. Munoz, X. Solans and M. Font-Bardia, Angew. Chem. Int. Ed., 1996, 35,

1485

CHAPTER 3

CHAPTER-3

MIXED-VALENCE LINEAR HOMO AND HETERO-TETRANUCLEAR

BIIIMnIIMnIIBIII, MnIIIMnIIMnIIMnIII, MnIVMnIIMnIIMnIV, FeIIIMnIIMnIIFeIII,

CrIIIMnIIMnIICrIII COMPLEXES : A MAGNETOSTRUCTURAL STUDY.

MAMMABMB

A Dinucleating Ligand Containing

Two Metal Centres

A Dinucleating Ligand Containing

Two Metal Centres

3.1 Introduction:

This chapter presents homo and hetero-tetranuclear complexes. Synthetic methods to

such species started with salen like ligands as binucleating agents, developed to acyclic

dicompartmental macrocyclic ligands and finally flourished at the beginning of the 90's,

with the baukasten or modular approach. Pathways to such complex molecular entities

are based on step-by-step strategies. This provides an efficient means to control both

nuclearity and dimensionality of the polymetallic systems. They are formed by two

modules e.g. [M(tmtacn)]n+ synthons, bridged by a coordinated oxime. The same

features are valid for heterotetranuclear complexes. As a result the complexes formed

follow the frames [MAMAMAMA] and [MAMBMBMA].

LINEAR TETRANUCLEAR OXIMATE COMPLEXES

At present the study of exchange interaction between paramagnetic metal centers

through various bridging ligands is an active research field in coordination chemistry

with the aim of understanding fundamental factors governing the magnetic properties of

transition metal compounds. Relatively few magnetic studies dealing with tetranuclear

systems have been reported in contrast to the large number of studies dealing with tri-

and bi-nuclear systems, primarily due to lack of fully structurally characterized

compounds and to the increased complexity involved with the theoretical treatments of

large spin systems. Most of the studies are concerned with homotetranuclear complexes,

although a few have treated heterometallic systems. New exchange pathways can be

expected for heteropolynuclear complexes,1-12 where unusual sets of magnetic orbitals

can be brought in close proximity; hence investigations of heteropolynuclear complexes

might be more informative in comparison to those of homopolynuclear complexes.

As part of the investigation into the magnetostructural studies of the binucleating

dioxime ligand 2,6-diformyl-4 methyl phenol dioxime (H3dfmp), and various homo and

heteropolynuclear complexes have been synthesized and designed to gain insight into

magnetostructural studies. Formation of binuclear transition metal complexes with

oxime ligands has been observed previously, notably with CuII and NiII. There have

been relatively few reports dealing with the coordination chemistry of 2,6-diformyl-4

methyl phenol dioxime and its derivatives.13-15, 23 In 1973 Okawa13 et al., reported the

reaction of 2,6-diformyl-4 methyl phenol with NH2OH in the presence of

Cu(CH3COO)2.H2O and NiCl2.6H2O respectively. Recently Thompson14 and co-

workers have reported magnetochemical and structural data on related a nickel(II)

oxime complex, Busch15 and co-workers have prepared asymmetric iminooxime

compartmental species, while Krebs et al., reported4 magnetostructural study on

heterometallic Fe2Ni2 cluster. But magnetostructural studies on manganese based

systems have not been explored, which motivated us to design manganese based homo

and heteropolynuclear complexes with an emphasis towards magnetostructural studies.

3.2 Synthesis:

This synthesis of the tetranuclear complexes involves five main steps. The first step is

the synthesis of the macrocyclic amine 1,4,7-triazacyclononane(Tacn), it's derivative

1,4,7-trimethyl-1,4,7-triazacyclononane(Me3Tacn) and the synthon [MA(Me3Tacn)Cl3]0

with the triamine facially coordinated and MA = Fe(III), Mn(III), and Cr(III). These

syntheses are well documented in the literature and therefore details are not given in this

CHAPTER 3

work. The organic precursor H3dfmp is synthesized as discussed previously and used

for the synthesis of the dinuclear precursors [(MA)2(dfmp)3]5- and [(MB)2(dfmp)3]5- and

finally the MAMAMAMA and MAMBMBMA complexes are synthesized.

A general schematic diagramme is given below:

Figure 3.1: Schematic diagram for the synthesis of linear tetranuclear complexes

3.2A Linear homo and hetero-tetranuclear complexes:

The following complexes were synthesized and characterized:

4. [(MeB)2MnII2(dfmp)3](Et3NH) where MeB came from methylboronic

acid[MeB(OH)2].

5. [(Me3Tacn)2 MnIII2MnII2(dfmp)3](ClO4)

6. [(Me3Tacn)2 MnIV2MnII2(dfmp)3](ClO4)3

7. [(Me3Tacn)2 FeIII2MnII2(dfmp)3](ClO4)

8. [(Me3Tacn)2 CrIII2MnII2(dfmp)3](ClO4)

and will be identified in the following section by their metallic cores, namely

BIIIMnIIMnIIBIII(4), MnIIIMnIIMnIIMnIII(5), MnIVMnIIMnIIMnIV(6),

FeIIIMnIIMnIIFeIII(7) and CrIIIMnIIMnIICrIII(8)

LINEAR TETRANUCLEAR OXIMATE COMPLEXES

This family of complexes illustrates how two simple tools such as the metal to

phenol dioximate molar ratio and the coordination properties of the terminal coligand

allow the synthetic chemist to design a great diversity of nuclearity tailored polynuclear

species. Each of these compounds was characterized by IR spectroscopy and elemental

analysis (C, H, N, metals). Mössbauer spectroscopy and temperature dependent

magnetic behavior were studied and the complexes were also characterized by

crystallographic techniques.

3.3 Infrared and Mass Spectroscopy:

The band in the IR spectra of the complex 4 at 2950 cm-1 corresponds to the C-H

stretching of the Et3NH group which present as a counteraction in the BIIIMnIIMnIIBIII

core. A moderately intense C=N stretching band for the ligand was observed at 1608

cm-1. Notable features are the sharp NO stretching bands at 1109, 1066 cm-1.

Complexes 5, 6, 7 and 8 also show C=N stretching bands for the ligand at 1608

cm-1. Strong peaks at 2918-2920 cm-1 correspond to the C-H stretching mode of the

Me3Tacn group present as the terminal ligand in the MnIIIMnIIMnIIMnIII,

MnIVMnIIMnIIMnIV, FeIIIMnIIMnIIFeIII, CrIIIMnIIMnIICrIII core congeners. The NO

stretching bands for all the linear tetranuclear complexes are observed at 1120, 1109

and1079 cm-1. Strong bands at 1080 and 624 cm-1 corresponds to the ClO4 unit which is

the counteranion in all four linear tetranuclear complexes. Though it is not possible to

distinguish the stretching frequencies for NO and ClO4 around 1080 cm-1 but the peak at

624 cm-1 confirms the presence of ClO4 group.

Electrospray-ioniziation mass spectrometry (ESI-MS) in the negative ion mode

has been proved to be very successful in characterizing BIIIMnIIMnIIBIII which shows the

mononegatively charged species [M-Et3NH]- as the base peak. On the other hand,

electrospray-ioniziation mass spectrometry (ESI-MS) in the positive ion mode is

successful in characterizing MnIIIMnIIMnIIMnIII (5), FeIIIMnIIMnIIFeIII (7) and

CrIIIMnIIMnIICrIII (8) which show monopositively charged species [M-ClO4]+ as the base

peaks, on the contrary the signal for [M-3ClO4]3+ of 6 is not found, but the base peak for

the fragment [M-2ClO4]2+ was observed.

CHAPTER 3

3.4 Solid state Structure

3.4.1 Solid-State Molecular Structure of [(MeB)2MnII2(dfmp)3](Et3NH) . C2H5OH

(4)

The lattice consists of discrete tetranuclear monoanions, triethylammonium

cations and ethanol molecules of crystallization. The X-ray structure clearly illustrates the

formation of the cage ligand. The X-ray structure confirms that a linear (180°)

tetranuclear complex has indeed been formed in such a way that each transition metal ion

shows octahedral geometry with two terminal B(III) ions and two Mn(II) as the central

ions are present in the lattice. The central tris(oximato)dimanganese(II) ion,

[Mn2(dfmp)3]5-, bridges two terminal B(III) centers through the deprotonated oxime

oxygen atoms. All phenoxy oxygen atoms are µ2-bridging yielding the Mn(2)......Mn(3)

separation of 2.909 Å.

Figure 3.2: ORTEP and labeling scheme for BIIIMnIIMnIIBIII (4)

The terminal B(III) ions, B(1) and B(4) have distorted tetrahedral geometry and are

bonded to one carbon atom from the methyl group and three oxygen atoms from the

bridging oximate oxygen groups. The B-O bond length is 1.50Å. An intramolecular

B(1)......B(4) separation of 8.864 Å has been found. The phenolate oxygen atoms O (23),

LINEAR TETRANUCLEAR OXIMATE COMPLEXES

O (38) , O (23) of three ligand sets dfmp3-, bridge two central manganese ions, Mn(2) and

Mn(3) giving rise to a face sharing bioctahedral core structure. The coordination

geometry around Mn(2) and Mn(3) are strongly trigonally distorted. Selected bond

lengths and angles of the B(O-N)3 Mn(µ2-O)3 Mn(N-O)3B core in 4 are given in

Table3.1. The Mn-O and Mn-N bond lengths for both manganese sites are not

significantly different (average 2.127 Å and 2.174 Å respectively), indicating the

equivalency of the sites. The three Mn(2)-O-Mn(3) bond angles are 86.67°, 86.04°, and

86.04°.

Table 3.1: Selected Bond Lengths (Å) and Angles (deg) for [(MeB)2MnII

2(dfmp)3](Et3NH) (4)

Mn(2)•••Mn(3) 2.909(5) B(1)•••B(4) 8.664

Mn(2)-O(38) 2.119(2) Mn(2)-O(23)-Mn(3) 86.03(6)

Mn(2)-O(23)≠1 2.122(2) Mn(2)-O(23)-Mn(3)≠1 86.03(6)

Mn(2)-O(23) 2.142(2) Mn(2)-O(38)-Mn(3) 86.68(8)

Mn(2)-N(32) 2.173(2)

Mn(2)-N(12) 2.174(2)

Mn(2)-N(20)≠1 2.175(2)

3.4.2 Solid-State Molecular Structure of [(Me3Tacn)2 MnIII2MnII2(dfmp)3](ClO4)

•CH3CN • C2H5OH (5)

The molecular geometry and atom labeling scheme of the trication in 5 are shown in

Figure 3.3. The structure of the complex molecule consists of a discrete monocationic

tetranuclear unit, one perchlorate anion with a molecule of acetonitrile and methanol as

solvents of crystallization. Selected bond lengths and angles are listed in Table 3.2. The

X-ray structure confirms that a linear (178°) tetranuclear complex has indeed been

formed in such a way that a tetrapseudooctaheral geometry containing four metal atoms,

two terminal Mn(III) and two Mn(II) as the central atoms are present in the lattice. The

central tris(oximato)dimanganese(II) ion, [Mn2(dfmp)3]5-, bridges two terminal Mn(III)

centers through the deprotonated oxime oxygen atoms. All phenoxy oxygen atoms are µ2-

bridging yielding a Mn(2)......Mn(3) separation of 3.043 Å. The terminal Mn(III) ions,

Mn(1) and Mn(4), are in distorted octahedral geometry with three nitrogen atoms form

CHAPTER 3

the facially coordinated tridentate macrocyclic amine and three oxygen atoms from the

bridging oxygen groups. The terminal Mn-O (average 1.944 Å) and the terminal Mn-N

(average 2.19 Å) bond lengths are consistent with those of implying a d4 high spin

electronic configuration of the terminal Mn(III) centers, Mn(1) and Mn(4). The N(7)-

Mn(1)-O(8) bond defines an elongated Jahn-Teller axis of a high-spin d4 ion in a

distorted octahedral ligand field. The average N-Mn-N angle is 85.2°, whereas O-Mn-O

angle is 98.46°. The Mn(1)......Mn(4) separation of 10.129 Å has been found.

The phenolate oxygen atoms O (53), O (73) , O (93) of the three dfmp3- ligands bridge

the two central manganese ions, Mn(2) and Mn(3) giving rise to a face sharing

bioctahedral core structure. The metrical details of the N3Mn(µ2-O)3MnN3 core in the

central part of 5 are briefly discussed in the following Table 3.2. The average Mn-N and

Mn-O bond distances are 2.218 Å and 2.183 Å respectively, correspond nicely to those

reported earlier. The coordination geometry of Mn(2) and Mn(3) are strongly trigonally

distorted. The bond lengths are in agreement with the high spin Mn(II) description of the

central Mn(2) and Mn(3) atoms. The three Mn(2)-O-Mn(3) bond angles are 88.1°, 88.3°,

and 88.7°. The three dioxime molecules are nearly planar. The dihedral angles between

the different planes comprising MnIII-O-N-MnII atoms lie in the ranges 29.95-34.07°

Figure 3.3: ORTEP and labeling scheme for MnIIIMnIIMnIIMnIII (5)

LINEAR TETRANUCLEAR OXIMATE COMPLEXES

Table 3.2: Selected Bond Lengths (Å) and Angles (deg) for [(Me3Tacn)

MnIII{(dfmp)3MnIIMnII}MnIII(Me3Tacn) ](ClO4) .CH3CN. CH3OH 5

Mn(1)•••Mn(2) 3.541 Mn(2)•••Mn(3) 3.043(3)

Mn(3)•••Mn(4) 3.547 Mn(1)•••Mn(4) 10.129

Mn(1)-N(1) 2.134(7) Mn(4)-N(21) 2.248(9)

Mn(1)-N(4) 2.119(8) Mn(4)-N(24) 2.229(8)

Mn(1)-N(7) 2.315(8) Mn(4)-N(27) 2.121(8)

Mn(1)-O(41) 1.888(6) Mn(4)-O(51) 1.976(7)

Mn(1)-O(61) 1.894(6) Mn(4)-O(71) 1.977(7)

Mn(1)-O(81) 2.063(7) Mn(4)-O(91) 1.866(7)

Mn(2)-N(42) 2.214(8) Mn(3)-N(50) 2.225(8)

Mn(2)-N(62) 2.231(8) Mn(3)-N(70) 2.23(8)

Mn(2)-N(82) 2.196(8) Mn(3)-N(90) 2.214(8)

Mn(2)-O(73) 2.20(6) Mn(3)-O(73) 2.17(6)

Mn(2)-O(93) 2.176(6) Mn(2)-O(93) 2.176(6)

Mn(2)-O(53)-Mn(3) 88.1(2)

Mn(2)-O(73)-Mn(3) 88.3(2)

Mn(2)-O(93)-Mn(3) 88.7(2)

3.4.3 Solid-State Molecular Structure of [(Me3Tacn)2 MnIV2MnII2(dfmp)3](ClO4)3

0.5 CH3CN • 1.5 H2O (6)

The molecular geometry and atom labeling scheme of the trication in 6 are shown in

Figure 3.4. The structure of the molecule consists of a discrete tricationic tetranuclear

unit, three perchlorate anions, 0.5 of the acetonitrile and 1.5 of water molecules as solvent

of crystallisation. Selected bond lengths and angles are listed in Table3.3. The X-ray

structure confirms that a linear 179° tetranuclear complex has indeed been formed and

similar with complex 5. The central tris(oximato)dimanganese(II) ion, [Mn2(dfmp)3]5-,

bridges two terminal Mn(IV) centers through the deprotonated oxime oxygen atoms. All

phenoxy oxygen atoms are µ2-bridging yielding the Mn(2)......Mn(3) separation of 2.947

Å. The terminal Mn(IV) ions, Mn(1) and Mn(4), are in distorted octahedral geometry

with three nitrogen atoms form the facially coordinated tridentate macrocyclic amine and

three oxygen atoms from the bridging oximate oxygen groups. The terminal Mn-O

CHAPTER 3

(average 1.848 Å) and the terminal Mn-N (average 2.09 Å) bond lengths are consistent

with d3 high spin electronic configuration of the terminal Mn(IV) centers, Mn(1) and

Mn(4). The N-Mn-N angle is 83.39°, whereas O-Mn-O angles fall between 98.49°. An

intramolecular Mn(1)......Mn(4) separation of 10.023 Å has been found.

The metrical details of the N3Mn(µ2-O)3MnN3 core in the central part of 6 is similar to

that of 4 and 5 and briefly discussed previously, so refraining from further elaboration.

The three Mn(2)-O-Mn(3) bond angles are 86.49°, 86.54°, and 86.14°. The three dioxime

molecules are nearly planar. The dihedral angles between the different planes comprising

MnIV-O-N-MnII atoms lie in the ranges 20.8-39.8°

Figure 3.4: ORTEP and labeling scheme for MnIVMnIIMnIIMnIV (6)

Table 3.3: Selected Bond Distances (Å) and Angles (deg) for

[(Me3Tacn)MnIV{(dfmp)3MnIIMnII}MnIV(Me3Tacn)](ClO4)3. 0.5 CH3CN. 1.5H2O 6

Mn(1)•••Mn(2) 3.538 Mn(2)•••Mn(3) 2.947(10)

Mn(3)•••Mn(4) 3.537 Mn(1)•••Mn(4) 10.023

Mn(1)-N(1) 2.092(4) Mn(4)-N(21) 2.090(4)

Mn(1)-N(4) 2.096(5) Mn(4)-N(24) 2.087(4)

Mn(1)-N(7) 2.084(4) Mn(4)-N(27) 2.093(4)

LINEAR TETRANUCLEAR OXIMATE COMPLEXES

Mn(1)-O(41) 1.847(3) Mn(4)-O(51) 1.837(3)

Mn(1)-O(61) 1.857(4) Mn(4)-O(71) 1.846(3)

Mn(1)-O(81) 1.841(4) Mn(4)-O(91) 1.862(3)

Mn(2)-N(42) 2.191(4) Mn(3)-N(50) 2.202(4)

Mn(2)-N(62) 2.192(4) Mn(3)-N(70) 2.204(4)

Mn(2)-N(82) 2.20(4) Mn(3)-N(90) 2.188(4)

Mn(2)-O(53) 2.156(3) Mn(3)-O(53) 2.146(3)

Mn(2)-O(73) 2.158(3) Mn(3)-O(73) 2.142(3)

Mn(2)-O(93) 2.141(3) Mn(2)-O(93) 2.175(3)

Mn(2)-O(53)-Mn(3) 86.49(12)

Mn(2)-O(73)-Mn(3) 86.54(12)

Mn(2)-O(93)-Mn(3) 86.14(12)

3.4.4 Solid-State Molecular Structure of [(Me3Tacn)2 FeIII2MnII2(dfmp)3](ClO4)

•0.5 CH2Cl2 • CH3CN (7)

The molecular geometry and atom labeling scheme of the trication in 7 is shown in

Figure 3.5. The structure of the molecule consists of a discrete monocationic tetranuclear

unit, one perchlorate anions, 0.5 of the dichloromethane and one acetonitrile molecules as

solvent of crystallization. Selected bond lengths and angles are listed in Table 3.4. The X-

ray structure confirms that a linear 179° tetranuclear complex has been formed and

similar with complexes 5 and 6, except two terminal Fe(III) ions instead of terminal

Mn(III) or Mn(IV) ions. The central tris(oximato)dimanganese(II) ion, [Mn2(dfmp)3]5-,

bridges two terminal Fe(III) centers through the deprotonated oxime oxygen atoms. All

phenoxy oxygen atoms are µ2-bridging yielding the Mn(2)......Mn(3) separation of 3.029

Å. The terminal Fe(III) ions, Fe(1) and Fe(4), are in distorted octahedral geometry with

three nitrogen atoms form the facially coordinated tridentate macrocyclic amine and three

oxygen atoms from the bridging oxygen atoms. The terminal Fe-O (average 1.925 Å) and

the terminal Fe-N (average 2.231 Å) bond lengths are consistent with d5 high spin

electronic configuration of the terminal Fe(III) centers, Fe(1) and Fe(4). The average N-

Fe-N angle is average 78.93°, whereas average O-Fe-O angle is 98.89°. An

intramolecular Fe(1)......Fe(4) separation of 10.034 Å has been found.

The central N3Mn(µ2-O)3MnN3 core in the 7 is similar with complexes 4, 5 and 6.

Selected bond lengths and angles are shown in Table 3.4. The three Mn(2)-O-Mn(3) bond

CHAPTER 3

angles are 87.92°, 88.12°, and 87.82°. The three dioxime molecules are nearly planar.

The dihedral angles between the different planes comprising FeIII-O-N-MnII atoms lie in

the ranges 29.02-33.98°

Figure 3.5: ORTEP and labeling scheme for FeIIIMnIIMnIIFeIII (7)

Table 3.4: Selected Bond Lengths (Å) and Angles (deg) for

[(Me3Tacn)FeIII{(dfmp)3MnIIMnII}FeIII(Me3Tacn)](ClO4) .0.5CH2Cl2 . 1CH3CN 7

Fe(1)•••Mn(2) 3.507 Mn(2)•••Mn(3) 3.029(5)

Mn(3)•••Fe(4) 3.498 Fe(1)•••Fe(4) 10.034

Fe(1)-N(1) 2.239(3) Fe(4)-N(21) 2.226(2)

Fe(1)-N(4) 2.232(2) Fe(4)-N(24) 2.234(3)

Fe(1)-N(7) 2.226(2) Fe(4)-N(27) 2.230(3)

Fe(1)-O(41) 1.938(2) Fe(4)-O(51) 1.907(2)

Fe(1)-O(61) 1.935(2) Fe(4)-O(71) 1.927(2)

Fe(1)-O(81) 1,917(2) Fe(4)-O(91) 1.923(2)

LINEAR TETRANUCLEAR OXIMATE COMPLEXES

Mn(2)-N(42) 2.228(2) Mn(3)-N(50) 2.206(2)

Mn(2)-N(62) 2.245(2) Mn(3)-N(70) 2.224(2)

Mn(2)-N(82) 2.192(2) Mn(3)-N(90) 2.229(2)

Mn(2)-O(53) 2.170(2) Mn(3)-O(53) 2.193(2)

Mn(2)-O(73) 2.179(2) Mn(3)-O(73) 2.177(2)

Mn(2)-O(93) 2.194(2) Mn(2)-O(93) 2.174(2)

Mn(2)-O(53)-Mn(3) 87.92(7)

Mn(2)-O(73)-Mn(3) 88.12(7)

Mn(2)-O(93)-Mn(3) 87.82(7)

3. 5 Mössbauer spectroscopy:

-4 -2 0 2 4

0.92

0.94

0.96

0.98

1.00

Relative Trnasmission

Velocity [mm s-1]

Figure 3.6 : Mössbauer spectrum of FeIIIMnIIMnIIFeIII (7)

The +3 oxidation state and the high spin electronic configuration of the iron centers in

complex 7 are confirmed by a Mössbauer spectrum recorded at 80 K and zero field. The

isomer shift (δ) and quadrupole splitting (EQ) obtained are 0.48 mms-1 and 0.42 mms-1

respectively. The isomer shift δFe around 0.5 mms-1 is of the magnitude expected for the

high spin ferric state and is close to the values reported for similar compounds.8,17

CHAPTER 3

3.6 Electrochemistry:

Cyclic voltamograms of complexes 4 and 5 were recorded in CH3CN solution containing

0.1 M nBu4PF6 in the potential range -2.25 to +1.25 V vs. Fc+/Fc. The CV of 4 afforded

one 2e reversible oxidation process at nearly same potential of 0.55V vs. Fc+/Fc, which is

shown in Figure 3.7. The oxidation is metal centred and represents the MnII/MnIII couple

of both central Mn(II) ions.

1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5

E [V] vs Fc+/ Fc

Complex 4

1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5

E [V] vs Fc+ / Fc

Complex 5

Figure 3.7: Cyclic Voltammogram for BIIIMnIIMnIIBIII (4) and MnIIIMnIIMnIIMnIII (5)

The CV of complex 5 afforded two consecutive reversible 2e oxidation processes in the

potential range 0.0V and 1.0 V vs. Fc+/Fc respectively and one 2e reversible reduction at

- 0.75V vs. Fc+/Fc. The first pair of oxidation may be assigned to a MnIII/MnIV couple

and the unambiguous evidence for this is the isolation of complex 6 in aerobic conditions

where the terminal manganese centers are at the +4 oxidation state compared to the +3

oxidation state of complex 5. The very similar oxidation potential for MnIII/MnIV

indicates very negligible electrostatic interaction. The second pair of oxidations can be

assigned to the central ions and it reflects that in aerobic conditions this process is highly

unfavourable due to the high oxidation potential. So the oxidation processes can be

expressed as:

MnIIIMnIIMnIIMnIII MnIV IV

MnIIMnIIMn MnIV IV

Ox1Ox2MnIIIMnIIIMn

LINEAR TETRANUCLEAR OXIMATE COMPLEXES

Analysis of cyclic voltammograms in the more negative potential range (- 0.75V) with

varying scan rates revealed one 2e reduction step attributable to the following equilibria:

MnIIIMnIIMnIIMnIII MnII II

Red1

III MnIV IV

MnIIMnIIMn

MnIIMnIIMn MnIIMnIIMn

All attempts to isolate the mixed valence complex of the form MnIVMnIIMnIIMnIII proved

to be unsuccessful. The comproportionation constant Kc for the equilibrium

2 MnIV III

MnIII MnIIMnIIMn

is calculated to be 22, which is too low for the isolation of the mixed valence species.

3.7 Magnetic Properties:

Magnetic susceptibility data for polycrystalline samples of the complexes were collected

in the temperature range 2-290 K in an applied magnetic field of 1T in order to

characterize the sign and magnitude of the magnetic exchange interaction in the modular

homo and hetero-tetranuclear systems. The analysis of the magnetic data was performed

using the Heisenberg-Dirac-Van Vleck (HDVV) model. The least squares fitting

computer programme JULIUS-F with a full matrix diagonalization approach was

employed to fit the temperature and field dependent magnetization. The programme uses

the spin -Hamiltonian operator, Htotal = Hz + Hzfs + HHDVV, where the exchange coupling is

described by HHDVV = - 2JS1.S2, the Zeeman interactions are given by Hz = µBBgiSi and

the axial single ion zero field splitting interaction is described by Hzfs = DSz2. Here we

use the Heisenberg spin Hamiltonian in the form, H = - 2JS1S2 for an isotropic exchange

coupling with S1 = S2 = S Mn (II) = 5/2 in case of complex 4 and a "two J" model was

applied to analyze the magnetic properties of this linear tetranuclear complexes and E = -

2J(S1S2 + S3S4) - 2J'S2S3 are employed where J = J12 = J34 and J' = J23 for 5, 6,7 and 8.

In the model, J = J12 = J34 represents the exchange coupling between adjacent metal

ions i.e., the terminal manganese and the central divalent manganese ions in case of

complexes 5 and 6, terminal iron and the central divalent manganese ions for complex 7

and terminal chromium and the central divalent manganese ions for complex 8, where as

J' = J23 describes the interaction between the central manganese nuclei within the linear

tetranuclear complex. Table 3.5 summarizes the intratetramer exchange parameters.

CHAPTER 3

The experimental effective magnetic moments (µeff) versus temperature (T) are

displayed in Figures 3.8 and 3.10. The magnetic moment per molecule of B2Mn2 (4) at

290 K is 7.12 µB (χM•T = 6.35 cm3.K.mol-1) and decreases monotonically with

decreasing temperature until it reaches 5.11 µB (χM•T = 3.27 cm3.K.mol-1) at 90 K and

then starts to decrease further but rapidly and reaches a value of 0.74 µB at 2 K.

50 100 150 200 250 300

µeff/µB

T/K

Figure 3.8: Magnetic data for BIIIMnIIMnIIBIII (4) as a plot of µeff vs. T. The bold points represent the

experimental data while the solid line represents the simulation

This temperature dependence magnetic moment is in agreement with

antiferromagnetic coupling between the neighbouring Mn(II) centers, resulting in a

diamagnetic ST = 0 ground state for 4. A simulation shown as a solid line in Figure 3.8

results in J = -8.4 cm-1, gMn = 1.98. The observed antiferromagnetic coupling agrees well

with the comparable exchange coupling constant reported earlier.24-26 The exchange

coupling constant J between the manganese ions where exchange coupling is mediated

through µ2-phenoxo group will be used in deriving the exchange interaction parameters

for the complexes 5-8.

The magnetic behaviour of MnIII2MnII2 (5) in the form of the effective magnetic

moments (µeff) versus temperature (T) is displayed in Figure 3.10a. The magnetic

moment of 9.41 µB (χM•T = 11.07 cm3.K.mol-1) at 290 K decreases monotonically with

decreasing temperature and until it reaches a value of 7.3 µB (χM•T = 6.65 cm3.K.mol-1)

LINEAR TETRANUCLEAR OXIMATE COMPLEXES

at 40 K and then starts to decrease further but rapidly and reaches a value of 2.51 µB at

2K. This temperature dependence magnetic moment is in agreement with

antiferromagnetic coupling.

To analyze the magnetic data at the beginning the model for a linear tetranuclear

complex with two terminal species S1 = S4 = SMn(III) = 2 and two central spins S2 = S3 =

SMn(II) = 5/2 were considered, as depicted in the following coupling scheme. The

parameter set, g1 = g4 = gMn(III) = 1.85 and g2 =g3 =gMn(II) = 2.0 and J12 = + 2.8 cm-1 and J23

= - 8.2 cm-1(comparable with the coupling constant obtained from the complex 4) were

obtained from the best simulation. The agreement between the calculated magnetic

moments is good as is evident from Figure 3.10a. The complex exhibit extremely

complicated low-lying structure with a non diamagnetic ground state which is not well

separated from the upper-lying states, is in full conformity with the non zero magnetic

moment at 2 K. The fit parameters were also checked by the 2D-contour plot (Figure

3.9a) of the exchange coupling constants and the global minima observed in the plot of

J12 and J23 show the value of J12 is undefined in the ferromagnetic scale and J23 = - 8.0

cm-1 is also quite satisfactory.

Mn1Mn2 Mn3 Mn4

J34

J23

= 4/2

for complex

J12

= 3/2

for complex 6

= 5/2

III

Scheme 1: Representation of the coupling scheme in complexes 5 and 6.

CHAPTER 3

Exchange interaction between neighbouring manganese (III) and (II) ions for

nioximate, glyoximate and also acetophenoximate complexes were reported18-20 to be

weak ferromagnetic (J~ +2 to +5 cm-1) in nature.

The magnetic behaviour of MnIV2MnII2 (6) is shown in Figure 3.10a in the form of

the effective magnetic moments (µeff) versus temperature (T). The magnetic moment of

10.37 µB (χM•T = 13.43 cm3.K.mol-1) at 290 K decreases monotonically with decreasing

temperature and reaches a value of 3.12 µB (χM•T = 1.22 cm3.K.mol-1) at 2 K. The

experimental magnetic data were simulated using a least squares fitting computer

programme with a full-matrix diagonalization approach and the solid line in Figure 3.10

represents the simulation. To analyze the magnetic data at the beginning the model for a

linear tetranuclear complex with two terminal species S1 = S4 = SMn(IV) = 3/2 and two

central spins S2 = S3 = SMn(II) = 5/2 were considered, as depicted in the following coupling

scheme. The parameter set, g1 = g4 = gMn(IV) = 2.0 and g2 =g3 =gMn(II) = 2.2 and J12 = 0.8

cm-1 and J23 = - 4.1 cm-1 were obtained from the best simulation. The agreement between

the calculated magnetic moments is good as is evident from Figure 3.10a. The

experimental results were also simulated with J12 = + 0.8 cm-1, J23 = -4.1 cm-1, and J13 =

+ 0.1 cm-1 but J13 is neglected as it is very small and by neglecting J13 a good fit was

obtained except some irrational g-values for the Mn(II) centers. This complex also

exhibits extremely complicated low-lying structure with a non-diamagnetic ground state,

which is not well separated from the upper-lying states, is in full conformity with the

non-zero magnetic moment at 2K

The fit parameters were also checked by the 2D-contour plot (Figure 3.9b) of the

exchange coupling constants and the global minima observed in the plot of J12 and J23

show the value of J12 is undefined in the ferromagnetic scale and J23 = - 4.2 cm-1 is also

quite satisfactory. It is to be noted here the exchange interaction between the central

manganese(II) ions is reduced compared two the same interaction in case of complex 4,

can be attributed in terms of decreasing separation between Mn(2)....Mn(3) [2.95 Å]

compared to the Mn(2)....Mn(3) [2,90 Å] in case of complex 4.

J23 J34

J12

LINEAR TETRANUCLEAR OXIMATE COMPLEXES

(a) (b)

Figure 3.9: Error surface plot for exchange coupling parameters in MnIIIMnIIMnIIMnIII and

MnIVMnIIMnIIMnIV core congeners

Exchange interactions between the neighbouring manganese (IV) and - (II) ions for

nioximate, glyoximate complexes were reported to be ferromagnetic (J~ +18 to +25 cm-1)

previously by our group.18a,21-22

The magnetic behaviour of FeIII2MnII2 (7) in the form of the effective magnetic

moments (µeff) versus temperature (T) are displayed in Figure 3.10b. The magnetic

moment of 10.66 µB (χM•T = 14.21 cm3.K.mol-1) at 290 K decreases monotonically with

decreasing temperature and until it reaches a value of 7.02 µB (χM•T = 6.17 cm3.K.mol-1)

at 20 K and then starts to decrease further but rapidly and reaches a value of 3.26 µB at

2K. This temperature dependence magnetic moment is in agreement with

antiferromagnetic coupling between the spin carriers. To analyze the magnetic data at the

beginning the model for a linear tetranuclear complex with two terminal species S1 = S4 =

SFe(III) = 5/2 and two central spins S2 = S3 = SMn(II) = 5/2 were considered, as depicted in

the following coupling scheme. The parameter set, g1 = g4 = gFe(III) = 2.0 and g2 =g3

=gMn(II) = 2.0 and J12 = -1.8 cm-1 and J23 = - 8.0 cm-1(comparable with the coupling

constant obtained from the complex 4) were obtained from the best simulation. The

agreement between the calculated magnetic moments is good as is evident from Figure

3.10b.

CHAPTER 3

Fe2

Mn1 Mn2

Fe1

= 5/2 for complex 7 = 5/2 = 3/2 for complex 8

J23 J34

J12

III

Scheme 2: Representation of the coupling Scheme in complexes 7 and 8.

The magnetic behaviour of CrIII2MnII2 (8) is shown in Figure 3.10b in the form of the

effective magnetic moments (µeff) versus temperature (T). The magnetic moment of 8.25

µB (χM•T = 8.53 cm3.K.mol-1) at 290 K decreases monotonically with decreasing

temperature and reaches a value of 2.18 µB (χM•T = 0.593 cm3.K.mol-1) at 1.95 K. The

experimental magnetic data were simulated using a least squares fitting computer

programme with a full-matrix diagonalization approach and the solid line in Figure 3.10b

represents the simulation. To analyze the magnetic data at the beginning the model for a

linear tetranuclear complex with two terminal species S1 = S4 = SCr(III) = 3/2 and two

central spins S2 = S3 = SMn(II) = 5/2 were considered, as depicted in the following coupling

scheme. The parameter set, g1 = g4 = gCr(III) = 1.9 and g2 =g3 =gMn(II) = 2.0 and J12 = - 2.4

cm-1 and J23 = - 8.75 cm-1(comparable with the coupling constant obtained from the

complex 4) were obtained from the best simulation. The agreement between the

calculated magnetic moments is good as is evident from Figure 3.10b.

LINEAR TETRANUCLEAR OXIMATE COMPLEXES

0 50 100 150 200 250 300

µeff / µB

T/K

(a)

50 100 150 200 250 300

T/K

µeff/µB

(b)

Figure 3.10: (a) Magnetic data for MnIIIMnIIMnIIMnIII (5) and MnIIIMnIIMnIIMnIII (6), as a plot of µeff

vs T. (b) Magnetic data for FeIIIMnIIMnIIFeIII (7) and CrIIIMnIIMnIICrIII (8) as a plot of µeff vs. T. The

bold points represent the experimental data while the solid line represents the simulation

CHAPTER 3

It is interesting to note that the related isoelectronic MnIVMnIIMnIIMnIV complex

exhibits ferromagnetic interaction between the MnIV...MnII center and this can be

attributable to the higher charge on the Mn(IV) center than that on the Cr(III) center.

Thus, the higher covalent character of the Mn(IV)-ligand bond leads to stronger

electronic interactions. Weak antiferromagnetic coupling between Cr(III) and Mn(II) ions

obtained is in contrast to the ferromagnetically coupled oximate complexes with

CrIIIMnIICrIII and CrIIIMnII core congeners.9,27

Table 3.5: Intratetramer magnetic parameters for homo-and heterotetranuclear complexes.

Compounds Magnetic core J12 [cm-1] J23[cm-1] gMn(II) gFe(III) gCr(III) gMn(III) or

gMn(IV)

4 MnIIMnII - 8.4 1.98

5 MnIIIMnIIMnIIMnIII J12 = J34 + 2.8 - 8.2 2.00

1.85

6 MnIVMnIIMnIIMnIV J12 = J34 + 0.8 - 4.1 2.00

2.00

7 FeIIIMnIIMnIIMnIII J12 = J34 - 1.8 - 8.0 2.00 2.00

8 CrIIIMnIIMnIICrIII J12 = J34 - 2.4 - 8.75 2.00 1.90

The nearest neighbour interaction, J is ferromagnetic in complexes 5 and 6, and

antiferromagnetic in complexes 7 and 8, while J' is antiferromagnetic in all the

complexes. Because of the competing influence of J and J' upon spin coupling in the

complexes 5-8, the ground state properties are determined by their ratios.

A qualitative rationale for the trend will now be provided and the nature of the

exchange interactions between neighboring MnIIIMnII, FeIIIMnII, MnIVMnII and MnIIMnII

spin carriers on the basis of the established Goodenough-Kanamori rules for

superexchange. The evaluated exchange coupling constants can be factored into two

opposing contributions from antiferromagnetic and ferromagnetic interactions with JAF

expressed as a negative term and JF as a positive term.

JT = JAF + JF

Considering the O and N atoms of the bridging oxime groups as sp2 hybridized in the

network M(O-N)3Mn and sp2 hybridization Mn(O)3Mn, the interaction parameters

evaluated from the magnetic data will be analyzed. Hence, the different possible

interactions of the sp2 orbitals on either side of the bridging oximate ligands with the

different orbitals in idealized D3h symmetry of the whole network MA(O-

N)3Mn(O)3Mn(O-N)3MA will be considered

LINEAR TETRANUCLEAR OXIMATE COMPLEXES

a1'

e''

a1'

e''

AFW

FeIII MnII

AFW

MnII

e'e'

e'' e''

a1'a1'

AFW

MnII

MnIII

a1'

e'' e''

AFW

MnII

MnIV

e'' e''

a1'a1'

Figure 3.11: Schematic diagram for magnetic exchange interaction

The five metal d orbitals with the 3-fold axis as the z-axis along the M...Mn vector

transform in D3h symmetry as a1' (dz2), e''(dxz,dyz) and e'(dx2-y2,dxy). Dominant exchange

paths are schematically represented, it is obvious from the above scheme that for the

FeIIIMnIIMnIIFeIII compound the antiferromagnetic path involving e' ⏐⏐sp2⏐⏐e'

interactions dominates over all other interactions, resulting in overall antiferromagnetic

interactions. Whereas in the MnIIIMnIIMnIIMnIII compounds interaction between the

MnII....MnII is involving dominating e' ⏐⏐sp2⏐⏐e' antiferromagnetic pathways, and the

antiferromagnetic pathways in MnII...MnIII is over compensated by the presence of

several ferromagnetic MnIII......MnII paths(e'⊥a1') and are important in determining the

strength of the overall exchange interactions. It is also to note that in the case of

MnIII......MnII with the missing electron in the e' orbital the AF path present in

FeIII......MnII vanished, resulting in stronger parallel coupling in d4(HS)d5 system. Now

on going to the MnIV...MnII, in which MnIV has an empty 2e orbital, the overall

interaction changes its nature from antiferromagnetic in FeIII...MnII to weak ferromagnetic

in MnIV...MnII (J = + 0.8 cm-1). Thus the contribution of the path e' ⏐⏐sp2 ⏐⏐e' to the

overall interaction becomes very important since the 2e orbitals centred on

CHAPTER 3

manganese(IV) and manganese(II) are empty and half-filled respectively leading to

ferromagnetic interaction. The π conjugated system of the 2,6-diformyl 4-methyl

phenoldioximato ligand delocalized over the bridging groups and perpendicular to the

plane of the oxime ligands, appears also to have a role, although small, in tuning the

exchange interactions in this series of compounds.

Tables 3.6 and 3.7 summarize exchange coupling constants reported in MnIIMnIII, MnIIMnIV,

MnIIFeIII and MnIICrIII core congeners, where exchange coupling mediated through oximate

(NO) ligands.

Table 3.6: Magnetic parameters for exchange coupled polynuclear oximate complexes

Compounds Magnetic

core

JMn(II)...Mn(III)

[cm-1]

JMn(II)...Mn(IV)

[cm-1]

gMn(III) gMn(II) gMn(IV) References

[(Me3Tacn)MnIII{(dmg)3MnII}

MnIII(Me3Tacn)](ClO4)2

MnIIIMnII + 4.7 + 19. 6 18a

[(Me3Tacn)Mn{(dmg)3Mn}Mn

(Me3Tacn)](ClO4)2

MnIVMnII 18a

[L2MnII2(µ-

O2COMe)(MeOH)MnIII]

(ClO4)2

MnIIIMnII + 2.0 1.98 2.05 18b

[(Me3Tacn)MnMn(PyA)3]

(ClO4)2

MnIIIMnII + 1.8 19

[(Me3Tacn)MnIII{(niox)3MnII}

MnIII(Me3Tacn)](ClO4)2

MnIIIMnII + 4.7 1.99 1.99 11

[(Me3Tacn)Mn{(niox)3Mn}

Mn(Me3Tacn)](ClO4)2

MnIVMnII + 25.2 2.00 2.00 11

[Mn3(MeO)2(pko)4(SCN)2] MnIVMnII + 3.06 2.09 2.09 21a

[Mn3(MeO)2(pko)4Cl2] MnIVMnII + 3.9 2.07 2.07 21b

[Mn3(MeO)2(pko)4(OCN)2] MnIVMnII + 4.05 2.08 2.08 21b

(Me4N)2[Mn4O2(cao)4(MeCN)2

(H2O)6](NO3)4

MnIIIMnII - 2.5 1.88 1.88 29

[Mn3(mcoe)6](NO3) MnIIIMnII - 1.3 ± 0.3 2.00 2.00 29

Table 3.7: Magnetic parameters for exchange coupled polynuclear oximate complexes

Compounds Magnetic core JFe(III)...Mn(II)

[cm-1]

JCr(III)...Mn(II)

[cm-1]

References

[(Me3Tacn)FeIIIMnII(PyA)3](ClO4)2FeIIIMnII - 6.0 8

[(Me3Tacn)CrIIIMnII(PyA)3](ClO4)2CrIIMnII + 1.5 9

[(Me3Tacn)FeIII{(dmg)3MnII}FeIII(Me3Tacn)](ClO4)2FeIIIMnIIFeIII - 6.7 28

[(Me3Tacn)CrIII{(dmg)3MnII}CrIII(Me3Tacn)](ClO4)2CrIIMnIICrIII + 4.5 27

LINEAR TETRANUCLEAR OXIMATE COMPLEXES

3.8 References:

(1) O. Kahn, Molecular Magnetism, VCH Publishers, Weinheim, 1993

(2) (a) O. Kahn. Adv. Inorg. Chem., 1995, 43, 179; (b) K. S. Murray. Adv. Inorg.

Chem., 1995, 43, 261

(3) F. Birkelbach, M.Winter, U. Flörke, H-J. Haupt, C. Butzlaff, M. Lengen, E. Bill,

A. X. Trautwein, K. Wieghardt and P. Chaudhuri, Inorg. Chem., 1994, 33, 3990

(4) C. Krebs, M.Winter, T. Weyhermüller, E. Bill, K.Wieghardt and P.Chaudhuri, J.

Chem. Soc., Chem. Commun., 1995, 1913

(5) P. Chaudhuri, M.Winter, P. Fleischhauer, W. Hasse, U. Flörke and H-J. Haupt, J.

Chem. Soc., Chem. Commun., 1990, 1728

(6) C. N. Verani, E. Rentschler, T. Weyhermüller, E. Bill and P. Chaudhuri, J. Chem.

Soc.,Dalton Trans., 2000, 4263

(7) C. N. Verani, T. Weyhermüller, E. Rentschler, E. Bill and P.Chaudhuri, J. Chem.

Soc., Chem. Commun., 1998, 2475

(8) S. Ross, T. Weyhermüller, E. Bill, E. Bothe, U. Flörke, K. Wieghardt and

P.Chaudhuri, Eur. J. Inorg. Chem., 2004, 984

(9) S. Ross, T. Weyhermüller, E. Bill, K. Wieghardt and P. Chaudhuri, Inorg. Chem.,

2001, 40, 6656

(10) C. N. Verani, E. Rentschler, T. Weyhermüller, E. Bill and P. Chaudhuri, J.

Chem. Soc., Dalton Trans ., 2000, 251

(11) F. Birkelbach, T. Weyhermüller, M. Lengen, M. Gerdan, A. X. Trautwein, K.

Wieghardt and P.Chaudhuri, J. Chem. Soc.,Dalton Trans., 1997, 4529

(12) A few selected examples: (a) S. Mohanta, K. K. Nanda, L. K. Thompson, U.

Flörke and K. Nag, Inorg. Chem., 1998, 37, 1465; (b) E. Colacio, J. M. Dominguez-

Vera, M.Ghazi, R. Kivekäs, M. Klinga and J. M. Moreno, Inorg. Chem., 1998, 37,

3040; (c) K. E. Vostrikova, D.Luneau, W.Wernsdorfer, P. Rey and M.Verdauger, J.

Am. Chem. Soc., 2000, 122, 718

(13) H. Okawa, T. Tokii, Y. Muto and S. Kida, Bull. Chem. Soc. Jpn., 1973, 46, 2624

(14) K. K. Nanda, A. W. Addison, N. Paterson, E. Sinn, L. K. Thompson and U.

Sakaguchi, Inorg. Chem., 1998, 37, 1028

(15) E. V. Rybak-Akimova, D. H. Busch, P. K. Kahol, N. Pinto, N. W. Alcock and

H. J. Clase, Inorg. Chem., 1997, 36, 510

(16) (a) Q. Zeng, S. Gou, L. He,Y. Gong and X.You, Inorg. Chim. Acta., 1999,

287,14; (b) P. Chakraborty and S. K. Chandra, Polyhedron., 1994, 13, 684

CHAPTER 3

(17) C. N. Verani, E. Bothe, D. Burdinsky, T. Weyhermüller, U. Flörke and P.

Chaudhuri, Eur. J. Inorg. Chem., 2001, 2161

(18) (a) F. Birkelbach, U. Flörke, H-J. Haupt, C. Butzlaff, A. X. Trautwein, K.

Wieghardt and P. Chaudhuri, Inorg. Chem., 1998, 37, 2000; (b) V.Pavlischuk, F.

Birkelbach, T. Weyhermüller, K. Wieghardt and P. Chaudhuri, Inorg. Chem., 2002,

41, 4405

(19)P. Chaudhuri, Coord. Chem. Rev., 2003, 243, 143

(20) P. Chaudhuri, E. Rentschler, F. Birkelbach, C. Krebs, E. Bill, T. Weyhermüller

and U. Flörke Eur. J. Inorg. Chem., 2003, 541

(21) M. Alexiou, C. Dendrinou-Samara, A. Kasagianni, S. Biswas, C. M. Zeleski, J.

Kampf, D. Yoder, J. E. Penner-Hahn, V. L. Pecoraro, D.P. Kessissoglou, Inorg.

Chem., 2003, 42, 2185

(22) T. Afrati, C. Dendrinou-Samara, C. P. Raptopoulou, A. Terzis, V. Tangoulis and

D. P. Kessissoglou, Angew. Chem.Int.Ed.Engl., 2002, 41, 2148

(23) D. Black, A. J. Black, K. P. Dancy, A. Harrison, M. Mcpartin, S. Parsons, P. A.

Tasker, G. Whittakar and M. Schroder, J. Chem. Soc.,Dalton Trans., 1998, 3953

(24) L. Dubois, Da-Feng.Xiang, Xian-Shi. Tan, J. Pecant, P. Jones, S. Bandron, L.

Le. Pape, J-M. Latour, C. Baffert, S. Chardon-Noblat, M. N. Coulomb and A.

Deronzier, Inorg. Chem., 2003, 42, 750

(25) S. Blanchard, G. Blondin, E. Riviere, M. Nierlich, J-J. Gireard, Inorg. Chem.,

2003, 42, 4568

(26) K. B. Jenson, E. Johanson, F. B. Larson, C. J. Mckenzie, Inorg. Chem., 2004,

43, 3801

(27) D. Burdinski, F. Birkelbach, T. Weyhermüller, U. Flörke, H-J. Haupt, M.

Lengen, A. X. Trautwein, E. Bill, K. Wieghardt and P. Chaudhuri, Inorg. Chem.,

1998, 37, 1009

(28) P. Chaudhuri and U. Flörke, unpublished result.

(29) D. J. Price, S. R. Batten, K. J. Berry, B. Moubaraki and K. S. Murray,

Polyhedron, 2003, 22, 165

LINEAR TETRANUCLEAR OXIMATE COMPLEXES

CHAPTER 4

CHAPTER - 4

HETEROTETRANUCLEAR [FeIII2CuII2], [CrIII2CuII2]

BUTTERFLY CORE CONGENERS

CuCu

Cu2

Cr3

Cr1

Cu4

4.1 Introduction

Tetranuclear oxide bridged metal assemblies are pertinent to several areas including

bioinorganic modelling and magnetochemistry. In the field of iron chemistry, the pursuit

of model complexes1-4 for the iron proteins has yielded several interesting tetranuclear

complexes amongst other polynuclear iron complexes with unusual electronic structures.5

The knowledge that in PSII the site of water oxidation, is a tetranuclear manganese

aggregate in which four manganese atoms are essential for activity. This appears to be in

close proximity to one another, has augmented the search for tetranuclear manganese

complexes. Thus tetramanganese butterfly complexes with the [Mn4O2]8+ core have

emerged as the most intensely studied oxide bridged carboxylate clusters.4,7-10

But there are few studies of the heterometallic butterfly complexes,11-13

despite the fact, that such studies might be more informative in comparison to those of

homometal complexes. Because new exchange pathways can be expected for

heteronuclear complexes14-26 where unusual sets of magnetic orbitals can be brought into

close proximity. For instance, the strict orthogonality of the magnetic orbitals resulting in

the stabilization of the spin state of highest multiplicity is much easier to realize in

heterometallic systems than in homometallic species.

TETRANUCLEAR "BUTTERFLY" CORE CONGENERS

There are several intriguing features associated with polynuclear clusters.

Firstly, these complexes can have unusual electronic structures and may serve as sources

of fundamental information about exchange coupling in multinuclear assemblies. A

second general reason to study polynuclear metal complexes is that, they may be building

blocks for molecular based magnetic materials. Because of their topology, molecules that

have large numbers of unpaired electrons should serve as good starting points for

constructing molecular magnetic materials.27 Though the pairwise exchange interactions

in these complexes are found almost always to be antiferromagnetic, spin frustration,28 or

competing spin interactions, can result in polynuclear complexes having relatively large

number of unpaired electrons in the ground state.

Additionally, designing molecular entities with interesting spin topologies

becomes easier with spin carriers of different kinds. Since the pioneering work of Olivier

Kahn in the magnetism of heterometallic systems, the field has developed tremendously,

as will be evident from the following discussion on the oximato-bridged tetranuclear

heterometallic molecules.

4.2 Synthesis:

The most successful synthetic strategy for heterometallic complex is the use of metal

complexes as ligands which can act as a building block for polynuclear complexes,

Therefore, metal complexes containing potential donor atoms can act as a bridging ligand

for another metal ion or metal complex with empty or available coordination sites. The

following strategy is an attempt to obtain heterometal complex, in which the oxime

ligand acting as a bridge between two different metal ions e.g. iron (III), copper(II) and

chromium(III), copper(II)

(a) dapdoH2

Ligands

(b)Me3Tacn

CHAPTER 4

The protonated oxime containing mononuclear complex32 [Cu(dapdoH2)2](ClO4)2 has

been reacted with either [Me3TacnFeIII]3+ or [Me3TacnCrIII]3+ unit in presence of

triethylamine. The assembly of these two building blocks(oxime complex as bridging

ligand and [Me3TacnMIII]3+ as capping ligand) in 1:2 molar ratio lead to the formation of

heterotetranuclear clusters [(Me3Tacn)FeIII2(dapdo)2CuII2(O...H...O)(µ2-Cl)](ClO4)2 9 and

[(Me3Tacn)CrIII2(dapdo)2CuII2(µ2-OH)2Br2](ClO4)2 10.

-ONN

NO-HO N N NOH

+ 1 MA

HO N NNOH

2 Me3TacnMB-Fragment

ONN

N= Me3Tacn

MBMB

O O

dapdo

Figure 4.1: Schematic diagram for the synthesis of "butterfly" core congeners 9-10

4.3 Infrared and Mass Spectroscopy:

Complexes 9 and 10 show the C=N stretching bands for the ligand at 1593 and 1595

cm-1 respectively. Strong peaks at 2916-2920 cm-1 correspond to the C-H stretching of

the Me3Tacn group, in the FeIII2CuII2 (9) and CrIII2CuII2 (10) core congeners. The NO

stretchings for these two tetranuclear complexes are observed at 1163 and 1080 cm-1.

Strong stretching bands at 1077, 624 cm-1 and 1090, 624 cm-1 respectively correspond to

the counteranion ClO4 unit in the tetranuclear FeIII2CuII2 and CrIII2CuII2 complexes.

TETRANUCLEAR "BUTTERFLY" CORE CONGENERS

Electrospray-ionaziation mass spectrometry (ESI-MS) in the positive ion mode has

been proved to be very successful in characterizing FeIII2CuII2 (9) which shows the

dipositively charged species [M-2ClO4]2+ as the base peak. The peak due to [M-ClO4]+ is

also observed. On the contrary, the signal for [M-2ClO4 + 0.5 H2O]2+ of 10 has been

found as the base peak.

4.4 Solid state molecular structure:

4.4.1 X-ray Structure of [(Me3Tacn)2FeIII2(dapdo)2CuII2(O...H...O)Cl](ClO4)2

.2CH3OH (5)

The lattice is built of discrete tetranuclear dication; two noncordinatively bound

perchlorate anions and two methanol molecules of crystallization. The molecular

geometry and atom labeling scheme of the cation 9 are shown in Figure 4.3. The cation

possesses a "butterfly" [Fe2(µ2-O...H...O-µ2)Cu2] core. Cu(1) and Cu(1A) occupy "body"

positions of the "butterfly" while Fe(1) and Fe(1A) occupy the "wing-tip" positions. The

O(1) and O(1A) are acting as double bridging oxo groups in each FeCu unit respectively.

The structure, thus, can be considered as two edge sharing FeCu2O triangular units as

shown below.

Fe(1)

Cu(1A)

Cu(1)

Fe(1A)

Cu(1)

Cu(1A)

Cu(1)

Cu(1A)

Fe(1) Fe(1A)

In addition to two µ2-Oxo groups, there is one µ2-Cl ion which acts as a bridge between

the "body" copper ions. Both the µ2-oxo groups are strongly hydrogen bonded with a

distance of 2.24 Å where H is detected crystallographically and gives rise to (O...H...O)

core. The 2,6-diacetylpyridine dioximate dianion ligands coordinate "body" Cu ions

through its pyridine N(32) and two oximate nitrogen N(22) and N(30) atoms. So the

CHAPTER 4

"body" Cu(II) ions are five coordinated with N3OCl distorted square pyramidal geometry

with the basal plane comprising two oximato nitrogen atoms, one pyridine nitrogen atom

and one µ2-oxo oxygen atom. The crystal structure gives τ value of 0.054 indicating an

essentially square-pyramidal (4 + 1) coordination geometry of the "body" copper ions.43

In a five coordinate system, ideally square pyramidal geometry is associated with α = β =

180° for A is the axial ligand (where α and β are the basal angles). In the great majority

of real square pyramidal systems, metal is displaced out of the equatorial plane toward

the axial ligand. The geometric parameter τ is defined as [( β - α) / 60] which is

applicable to five coordinate environment as an index of degree of trigonality, within the

structural continuum between trigonal bipyramidal and square pyramidal geometries. τ is

zero for a perfectly square pyramidal geometry, while it becomes unity for a perfect

trigonal bipyramidal geometry. The average Nox-Cu bond length is 2.056(15) Å, is

significantly longer than the Npy-Cu bond distance of 1.94(15) Å. The Cu-Cl bond

distance is 2.539(5) Å and gives rise to Cu(1)-Cl(1)-Cu(1A) angle 87.91°,whereas the

bond distance between Cu(1) and O(1) is 1.913(12) Å.

The coordination geometry of the "wing-tip" ferric ion Fe(1) is distorted

octahedral, with the three nitrogen atoms N(1), N(4) and N(7) from the facially

coordinated tridentate macrocyclic amine(Me3Tacn) and three oxygen atoms [O(21) and

O(31) from the deprotonated oxime group, O(1) from the µ2-bridging oxo group]

resulting in a fac-FeN3O3 coordination sphere. The Fe-N(average 2.24 Å) and Fe-

O(average 1.99 Å) distances are in agreement with a d5 high-spin electronic configuration

for the iron center. The Fe(1)-µ2-oxo distance is [1.856(12) Å], as expected, the shortest

among metal-ligand bond lengths. The Fe(1) is displaced by 0.046 Å from the mean basal

plane comprising N(4)N(7)O(21)O(31) toward the apical µ2-oxygen atom O(1). Selected

bond lengths and angles for the FeIII2CuII2O2 core are given in Table 4.1. The Fe-N

distance trans to the µ2-oxo group [Fe(1)-N(1) = 2.259(15) Å] is longer than the other Fe-

N distances. A deviation from idealized octahedral geometry at the metal center is found

for the capping ligand Me3Tacn; the N-Fe-O angles lying in the ranges 77.72° to 78.71°,

whereas O-Fe-O angles fall between 93.25 and 102.23°. The Fe(1)...Cu(1) and

Fe(1A).....Cu(1A) separations of 3.29 Å are significantly shorter than the Fe(1)....Cu(1A)

and Cu(1)....Fe(1A) separations of 4.020 Å. The "body" Cu(1).....Cu(1A) separation is

about 3.526 Å, while the separation between the "wing-tip" Fe(1).....Fe(1A) is 5.442 Å.

TETRANUCLEAR "BUTTERFLY" CORE CONGENERS

Figure 4.3: ORTEP and labeling scheme for the dication FeIII

2CuII

(9)

Table 4.1: Selected Bond Lengths (Å) and Angles (deg) for [(Me3Tacn)FeIII{(dapdo)2CuII2

}(O....OH)ClFeIII(Me3Tacn)](ClO4)2 .2 CH3OH 9

Table 4.1: Selected Bond Lengths (Å) and Angles (deg) for [(Me3Tacn)FeIII{(dapdo)2CuII2

}(O....OH)ClFeIII(Me3Tacn)](ClO4)2 .2 CH3OH 9

Fe(1)•••Cu(1) Fe(1)•••Cu(1) 3.239 3.239 Cu(1A)•••Fe(1A) Cu(1A)•••Fe(1A) 4.020 4.020

Fe(1A) •••Cu(1) 3.239 Fe(1)•••Fe(1A) 5.442

Fe(1)•••Cu(1A) 4.020 Cu(1A)•••Cu(1) 3.526

Cu(1)-N(22) 2.009(15) Cu(1)-N(22) 2.009(15)

Cu(1)-N(30) 2.112(15) Cu(1A)-N(30) 2.112(15)

Cu(1)-N(32) 1.936(15) Cu(1A)-N(32) 1.936(15)

Cu(1)-O(1) 1.913(12) Cu(1A)-O(1) 1.913(12)

Cu(1)-Cl(1) 2.539(5) Cu(1A)-Cl(1) 2.539(5)

Fe(1)-N(1) 2.259(15) Fe(1A)-N(1) 2.259(15)

Fe(1)-N(4) 2.228(16) Fe(1A)-N(4) 2.228(16)

Fe(1)-N(7) 2.250(15) Fe(1A)-N(7) 2.250(15)

Fe(1)-O(1) 1.856(12) Fe(1A)-O(1) 1.856(12)

Fe(1)-O(21) 2.014(13) Fe(1A)-O(21) 2.014(13)

Fe(1)-O(31) 1.966(13) Fe(1A)-O(31) 1.966(13)

Fe(1)-O(1)-Cu(1) 118.46(7)

CHAPTER 4

Cu(1)-Cl(1)-Cu(1A) 87.91(2)

O(1)-Fe(1)-N(1) 168.8(6)

O(21)-Fe(1)-N(4) 159.68(5)

O(31)-Fe(1)-N(7) 161.59(6)

4.4.2 X-ray Structure of [[(Me3Tacn)2CrIII2(dapdo)2CuII2(OH)2Br2](ClO4)2 .3CH3CN

. 0.5 H2O (10)

The lattice is built of discrete tetranuclear dication, two noncordinatively bound

perchlorate anions, three acetonitrile molecules and half water molecule of

crystallization. The molecular geometry and atom labeling scheme of the cation 10 are

shown in Figure 4.4. The cation possesses a "butterfly" [Cr2(µ2-OH)2Cu2] core. Cu(1) and

Cu(2) occupy "body" positions while Cr(1) and Cr(2) occupy the "wing-tip" positions of

the "butterfly". The O(100) and O(200) atoms are acting as double bridging hydroxo

groups in each CrCu unit respectively. The structure, thus, can be considered as two edge

sharing CrCu2OH triangular units as shown below.

Cr(1)

Cu(2)

Cu(1)

Cr(2)

Cu(1)

Cu(2)

Cu(1)

Cu(2)

Cr(1) Cr(2)

Both the µ2-hydroxo groups are strongly hydrogen bonded with a distance of 2.9 Å, and

gives rise to (O...HO) core. The 2,6-diacetylpyridine dioximate dianion coordinate to

Cu(1) through its pyridine N(52) and two oximate nitrogen atoms N(42) and N(50)

atoms, the average Nox-Cu bond length is 2.07(2) Å is significantly longer than the Npy-

Cu bond distance of 1.93(2) Å, whereas the bond distance between Cu(1) and O(200) is

TETRANUCLEAR "BUTTERFLY" CORE CONGENERS

1.976(13) Å. The fifth position of the copper ion is satisfied by axial Br(1) and thus

"body" Cu ions Cu(1) and Cu(2) are in N3OBr coordination sphere with square pyramidal

geometry (τ value is calculated to be 0.09) around the copper centers.

Figure 4.4: ORTEP and labeling scheme of the dication of CrIII

2CuII

(10)

The coordination geometry of the "wing-tip" chromium ion Cr(1) is distorted octahedral,

with the three nitrogen atoms N(1), N(4) and N(7) from the facially coordinated tridentate

macrocyclic amine(Me3Tacn) and three oxygen atoms [O(41) and O(61) from the

deprotonated oxime groups, O(200) from the µ2-bridging hydroxo group] resulting in a

fac-CrN3O3 coordination sphere. The Cr-N [average 2.212(2) Å) and Cr-Oox(average 1.95

Å) distances are in agreement with a d3 high-spin electronic configuration for the

chromium center. The Cr(1)-µ2- hydroxo distance is 1.98(13) Å, as expected for

chromium-hydroxo bond length. The Cr(1) is displaced by 0.688 Å from the mean basal

CHAPTER 4

plane comprising N(4)N(7)O(41)O(61) toward the apical µ2-oxygen atom O(200).

Selected bond lengths and angles for the CrIII2CuII2(OH)2 core for the cation are given in

Table 4.2. A deviation from idealized octahedral geometry at the metal center is found for

the capping ligand Me3Tacn; the N-Cr-O angles are lying in the ranges 82.02° to 82.96°,

whereas O-Cr-O angles are found to be in the ranges 93.18 and 94.13°. The Cr(1)...Cu(1)

separation of 3.3 Å is significantly shorter than the Cr(1)....Cu(2) separation of 4.377 Å.

The "body" Cu(1).....Cu(2) separation is about 3.453 Å, while the separation between the

"wing-tip" Cr(1).....Cr(2) is 5.948 Å.

Table4.2: Selected Bond Lengths (Å) and Angles (deg) for [(Me3Tacn)CrIII{(dapdo)2CuII2

}(OH)2Br2CrIII(Me3Tacn)](ClO4)2 3CH3CN . 0.5H2O 10

Cr(1)•••Cu(1) 3.313 Cu(2)•••Cr(2) 3.296

Cr(1)•••Cu(2) 4.377 Cr(1)•••Cr(2) 5.948

Cu(1) •••Cu(2) 3.453 Cu(1) •••Cr(2) 4.332

Cu(1)-N(42) 2.012(15) Cu(2)-N(62) 2.139(2)

Cu(1)-N(50) 2.133(15) Cu(2)-N(70) 2.020(2)

Cu(1)-N(52) 1.926(15) Cu(2)-N(72) 1.932(2)

Cu(1)-O(200) 1.976(13) Cu(2)-O(100) 1.946(14)

Cu(1)-Br(1) 2.6013(3) Cu(2)-Br(2) 2.587(3)

Cr(1)-N(1) 2.125(2) Cr(2)-N(21) 2.125(2)

Cr(1)-N(4) 2.117(2) Cr(2)-N(24) 2.114(2)

Cr(1)-N(7) 2.115(2) Cr(2)-N(27) 2.128(2)

Cr(1)-O(200) 1.976(13) Cr(2)-O(100) 1.958(13)

Cr(1)-O(41) 1.956(14) Cr(2)-O(51) 1.956(14)

Cr(1)-O(61) 1.951(14) Cr(2)-O(71) 1.956(14)

Cu(2)-O(100)-Cr(2) 115.17(7)

Cu(1)-O(200)-Cr(1) 113.9(6)

O(61)-Cr(1)-N(1) 172.83(6)

O(41)-Cr(1)-N(4) 169.94(9)

O(200)-Cr(1)-N(7) 176.67(7)

TETRANUCLEAR "BUTTERFLY" CORE CONGENERS

4.5 Magnetic Properties:

Magnetic susceptibility data for polycrystalline samples of the complexes were

collected in the temperature range 2-290 K in an applied magnetic field of 1 T. We use

the Heisenberg spin Hamiltonian in the form H = -2JA(S1S2 + S3S4) - 2JB (S1S4 + S2S3) -

2JCS2S4 (for complex 9) and H = -2JA(S1S2 + S3S4) - 2JB (S1S4 + S2S3) (for complex 10)

for an isotropic exchange coupling with S1 = S3 = SFe = 5/2, S2 = S4 = SCu = 1/2 for 9, and

S1 = S3 = SCr = 3/2, S2 = S4 = SCu = 1/2 for 10. The experimental data as the effective

magnetic moments (µeff) versus temperature (T) are displayed in Figures 4.6 and 4.8

respectively. The experimental magnetic data are simulated using a least squares fitting

computer program with a full-matrix diagonalization approach and the solid lines in

Figures 4.6 and 4.8 represent the simulations. Table 4.5 summarizes intratetramer

exchange parameters

The magnetic moment µeff/molecule for 9, FeIII2CuII2, of 7.24 µB (χM•T = 6.55

cm3•K•mol-1) at 290 K, is smaller than the spin only value of χM•T (g = 2) for a unit

composed of noninteracting [FeIII2CuII2] ions is 10.25 cm3•K•mol-1 and increases

monotonically with decreasing temperature until it reaches a value of 8.2 µB (χM•T =

8.41 cm3•K•mol-1) at 5 K and then starts to decreases and reaches a value of 7.02 µB

(χM•T = 6.15 cm3•K•mol-1) at 2 K. Hence the molecule appears to have a high-spin

ground state, with the low temperature decrease assigned to some contribution from zero-

field splitting (D). This temperature dependence behavior is in agreement with a non

diamagnetic ground state, is evidenced from the µeff value at 2 K.

From the temperature dependence of the magnetic behavior of complex 9, it can

be thought of ferromagnetic exchange interaction between the spin carriers but this kind

of nature is also possible due to the presence of different competing spin interactions. The

total spin (ST) values of the different resultant states range from 0 to 6. For a molecule

such as 9 with very low symmetry, different exchange parameters Jij are theoretically

required for each possible pairwise exchange interactions between FeIII...CuII, CuII...CuII

and FeIII...FeIII centers. In such a case, the determination of different J parameters would

yield unreliable and correlating values. The exchange parameters between the "wing-tip"

Fe(III) is assumed to be zero given the large distance between Fe(1) and Fe(1A) [5.442 Å

]. There are two different kinds of exchange interactions between the "wing-tip" Fe(III)

and "body" Cu(II) centers. Inspection of the molecular structure of 9 reveals that there are

three main exchange pathways.

CHAPTER 4

Cu2

Fe1

Cu4

Fe3

Figure 4.5: Perspective view of coupling scheme. ( JA = J12 = J34 = Jwb, JB = J23 = J14 = Jwb', JC = J24 =

Jbb)

III

Scheme 1

The first exchange pathway JA = J12 = J34 (Jwb) refers to the FeIII(O)(NO)CuII interaction,

second one, JB = J14 = J23 (Jwb') refers to the FeIII(NO)CuII interaction and the third

pathway JC = J24 (Jbb) refers to the CuII(Cl)CuII interaction. So the magnetic exchange

coupling (JA) between iron (III) and copper(II) is mediated through different bridges [a

two atom N-O bridge and through oxo bridge], on the other hand the magnetic exchange

coupling (JB) between iron (III) and copper(II) is mediated through a two atom N-O

bridge. It is to be noted here that the dominated exchange interaction pathways are via the

µ2-O2- groups not the oximate (N-O) transmitters. So from the magnetochemical view

point, only three J values are required: JA = Jwb = J12 = J34, JB = Jwb' = J14 = J23 and JC = Jbb

= J24; where w = wing-tip and b = body. The full-matrix diagonalization of the spin

TETRANUCLEAR "BUTTERFLY" CORE CONGENERS

Hamiltonian matrix produced best fit parameters: JA = J12 = J34 = - 125 cm-1; JB = J14 =J23

= - 6 cm-1 and J24 = - 50 cm-1 with g1 = g3 = 2.01 and g2 = g4 = 2.04. So, the data for

complex 9 is analyzed with a "three-J" model. The exchange coupling between the high

spin iron(III) and copper(II) is antiferromagnetic on the basis of Goodenough-Kanamori33

rules. In the analysis, two different iron(III)-copper(II) magnetic exchange interactions

are taken into consideration. The exchange coupling is expected to be much stronger in

case of JA compared to JB, due to the presence of an oxo transmitter. In the past some

authors have proposed an oxide ligand as possibly mediating the antiferromagnetic

coupling in the heme-copper site for the fully oxidized enzyme. It has been reported34 that

all oxo-and hydroxo bridged FeIIICuII adducts exhibit strong antiferromagnetic coupling.

In general, oxo bridged dinuclear FeIIICuII core of compounds exhibit near linear Fe-O-

Cu linkage, which makes favourable overlap between the magnetic orbitals and is

reflected in strong antiferromagnetic exchange interactions. Magnetic exchange

interaction parameters of these kind of complexes are listed in Table 4.3.

Table 4.3: Magnetic parameter of some FeIII(O)CuII cores

Compounds Magnetic core JFe(III)...Cu(II)

[cm-1]

Fe-O-Cu

(bond angle in deg.)

References

[(F8TPP)Fe-O-

Cu(TMPA)]+

FeIIICuII - 174.0 178 34c

[(OEP)Fe-O-

Cu(Me6tren)]+

FeIIICuII ≥ - 200.0 180 34f

[(L)Fe-O-Cu]+FeIIICuII > - 200.0 171 34g

[(F8TPP)Fe-OH-

Cu(TMPA)]2+

FeIIICuII - 144.0 157 34b

[(OEP)Fe-O-

Cu(Me5tren)(ClO4)]+

FeIIICuII - 170.0 157 34d

The environment around the Cu(II) ions in complex 9 is square pyramidal

which is observed from the structural parameters, with an unpaired electron in the dx2-y2

orbital. Thus the strong magnetic interactions can be interpreted as the symmetry allowed

Fe(dx2-y2) ⎜⎜(O) ⎜⎜Cu(dx2-y2) (using Ginsberg symbols) σ-superexchange pathway. The

dx2-y2 magnetic orbitals of FeIII and CuII ions also interact through the oximato (NO)

group, and the strong magnetic interaction is expected as the symmetry allowed Fe(dx2-y2)

⎜⎜σNO⎜⎜Cu(dx2-y2) pathway. The overall exchange coupling constant J results from

individual antiferromagnetic and ferromagnetic exchange interactions: J = JAF + JF. The

CHAPTER 4

ferromagnetic contributions provided by the dx2-y2 ⊥σNO⎜⎜t2g exchange paths can not

balance the dominant antiferromagnetic interaction, leading to an effective antiparallel

spin coupling between FeIII and CuII centers. The following diagram shows the

orientation of the relevant orbitals for the mechanism of interaction.

Fe Cu

The reported antiferromagnetic exchange coupling between iron (III) and copper(II)

through oxo transmitter in case of synthetic models for heme copper oxidases34lie in the

ranges of - 80 to - 200 cm-1(based on H = - 2JSiSj model). In these heterobinuclear

iron(III)-copper(II) complexes exchange interaction which mediates through oxo

transmitter is found to be stronger due to the near linear arrangement, which makes the

Fe-O-Cu angle of nearly 180°. In case of complex 9, it is observed that the Fe-O-Cu bond

angle is 118.46(7)°, thus the exchange coupling constant is expected to be lower

compared to the values obtained in the complexes reported by Holm34d,e and Karlin.34a,b,c

The oximate (N-O) group also contributes in the exchange coupling constant (Jwb = JA)

and this contribution is also antiferromagnetic in nature and thus, makes the overall

exchange coupling (JA) to be stronger in magnitude. The investigation of exchange

interactions as a function of dn- electronic configuration where a two atom N-O bridge is

the transmitter, reported11,21,31 to be in the ranges of - 40 to - 60 cm-1. Some literature

values of the exchange interactions mediated through oximato (NO) transmitter between

high-spin Fe(III) and Cu(II) ions is listed in Table 4.4. It has been observed that,

exchange coupling constant between high spin Fe(III) and Cu(II) (through N-O

transmitter) is - 20 cm-1 in the FeIIICuIINiII complex20 and even is lesser in magnitude (- 5

cm-1) in the FeIIICuIICuII complex reported by Verani et.al.19 So in case of complex 9

strong antiferromagnetic coupling (JA = J12 = J34) between FeIII-CuII (through oxo and

oximate bridges) predominates over antiferromagnetic exchange coupling (JB = J14 = J23),

and the values obtained from simulation is comparable to the values reported earlier.

TETRANUCLEAR "BUTTERFLY" CORE CONGENERS

Table 4.4: Magnetic parameters of FeIIICuII oximate complexes

Compounds Magnetic core JFe(III)...Cu(II)

[cm-1] References

[(Me3Tacn)FeIII{(dmg)3CuII}

FeIII(Me3Tacn)](ClO4)2

FeIIICuIIFeIII - 42.0 18

[(Dopn)CuII(OH2)FeIII(Cl)

(Me3Tacn)](ClO4)2

CuIIFeIII - 38.8 16

[(Me3Tacn)FeIII(Cl)CuII

(MeOH)NiII(MeOH)2Lox]

(ClO4)2

FeIIICuIINiII - 20.0 20

[(Me3Tacn)FeIII(Cl)CuII(H2O)

uII(H2O)Lox](ClO4)2

FeIIICuIICuII - 5.0 19

[(Me3Tacn)FeIIICuII(PyA)3]

(ClO4)2

FeIIICuII - 53.0 21

The exchange coupling between the "body" copper (II) ions was evaluated to be - 50 cm-

1, mediated through µ2-Cl bridge. The magnetic properties of a number of bis (µ-chloro)

copper(II) dimers have been studied and most of them exhibit antiferromagnetic spin

coupling. For the dichloride bridged dicopper(II) system, an empirical relationship has

been developed between the exchange coupling constant and ϕ / R (ϕ is the Cu-Cl-Cu

angle and R is the longer Cu-Cl separation). According to the relationship, the

antiferromagnetic interaction would become more significant with increasing ϕ / R (when

ϕ / R > 33).41 However copper(II) compounds with a monochloride ion bridge are very

few and there is no magnetostructural relationship developed. In the present case the two

body copper atoms bridged by a chloride ion (ϕ / R = 34.6), are in axial position and due

to the square pyramidal environment of copper(II) ions, the unpaired electron resides in

copper ions mainly in the dx2-y2 orbital. According to the orbital overlap between copper

ions and the bridging chloride ligand, a weak coupling is expected. Weak ferromagnetic

to strong antiferromagnetic exchange coupling interactions through µ-chloro bridge

ligand are reported in literature.42 Hendrickson and co-workers pointed out that the value

of Jwb can be well determined, but the value of Jbb not. Since Jwb is much stronger than

Jbb and there are four "wing-body" interactions (two Jwb and two Jwb') and only one Jbb, the

spin-manifold energies are primarily determined by "wing-body" interactions, making the

precise value of Jbb indeterminate. Tetranuclear FeIII2CuII2 "butterfly" complex is regarded

as an example exhibiting spin frustration. The strong antiferromagnetic "wing-body"

interactions frustrate the weaker "body-body" interaction leading to the ST = 4 ground

state via the spin alignments shown pictorially in scheme1 i.e., the CuII(body) spins are

polarized ferromagnetically, although the intrinsic interaction between these ions is

antiferromagnetic. Competing interactions are evidently not limited to triangular

CHAPTER 4

topologies. They occur in all cases where there is a competition between different

exchange interactions. In a certain sense the uncertainty in body-body interaction is the

mathematical response to this competition between antagonist factors. It should be

remembered that the topology sometimes creates a ferromagnetic polarization between

two antiferromagnetically coupled spin carriers. The competition between these two

opposite forces may lead to ground states that can not be described in the simple fashion

of combining the local spins assimilated to classical vectors.

To determine the spin ground state, magnetization data were collected at 1, 4 and 7 T in

the temperature range 2-290 K and plotted as reduced magnetization (M/Ngβ) vs (βH/kT)

(vide infra), where N is the avogadro's number, β is the Bohr magneton and k is the

Boltzmann's constant. For a system occupying only the ground state and experiencing no

zero-field splitting (D), the various isofield lines would be superimposed and M/Ngβ

would saturate at a value ST. The non-superposition of the variable temperature variable

field (VTVH) plots at low temperature clearly indicates the presence of zero-field

splitting (ZFS or D). Reduced magnetization measurement yielded a ground state ST > 3

but < 4. According to the spin coupling scheme ground state ST = 4 could be expected,

but ST < 4 could be due to the intermolecular interaction or zero-field splitting (D) of the

ground state.

Attempts to fit the data by using the method of full-matrix diagonalization of the spin

Hamiltonian matrix including axial ZFS, with the pairwise exchange interactions,

produced best fit parameters: Jwb = JA = J12 = J34 = - 125.0 cm-1, Jwb' = JB = J14 = J23 = -

5.0 cm-1, Jbb = JC = - 50 cm-1 with DFe = + 2.7 cm-1. With DFe = - 2.7 cm-1 (fixed) a fit

with poorer quality than that with positive D was obtained. The values of zero field

splitting, DFe = + 2.7 cm-1 from the best fit, is also quite similar to the value obtained (DFe

= ⎢2.2 ⎢ cm-1) in case of FeIIICuII complex reported by Ross et al.21 For comparison it is to

be mentioned, that for a dinucler FeIIICuII complex reported40 by Kahn et. al, observed

spin Hamiltonian parameters are, JFe-Cu = - 78 cm-1, DFe = + 11.8 cm-1 and DS = 2 = + 7.8

cm-1.

TETRANUCLEAR "BUTTERFLY" CORE CONGENERS

0,0 0,5 1,0 1,5 2,0 2,5

M/Ngß

ßH/kT

1 T

4 T

7 T

50 100 150 200 250 300

7.2

7.4

7.6

7.8

8.0

8.2

8.4

µeff / µB

T/K

Figure 4.6: Magnetic data for FeIII

2CuII

(9) plot of µeff vs T and M/Ngß vs ßH/kT. The bold points

represent the experimental data while the solid line represents the simulation.

It has been shown in detail by Hendrickson2,7-8 and co-workers that, in the case of spin

frustration, subtle changes in the ratios of competing exchange interactions in a

polynuclear transition metal complexes can have dramatic effects on the exact nature of

the ground and low-lying states. It is the ratio of competing exchange interactions and not

so much their absolute magnitudes which characterizes the electronic structure of these

complexes. The ground state of the present complex represents ST = 4. This result is in

accord with the analysis made by Hendrickson that, when competing exchange

interactions are antiferromagnetic and are of similar magnitude, the complex will have a

ground state with the smallest ST value. In the case of FeIII2CuII2 "butterfly" core congener

Fe...Cu and Cu...Cu interactions are not of similar magnitudes and that stabilizes a high-

spin ground state, as is evidenced from the VTVH magnetic measurement.

The magnetic moment µeff/molecule for 10, CrIII2CuII2, of 4.9 µB

(χM•T = 3.0 cm3•K•mol-1) at 290 K decreases monotonically with decreasing

temperature until it reaches a value of 4.39 µB (χM•T = 8.41 cm3•K•mol-1) at 100 K and

then starts to increases and reaches a value of 4.84 µB (χM•T = 2.92 cm3•K•mol-1) at 15

CHAPTER 4

K and then finally decreases to a value of 4.58 µB. This temperature dependence is in

agreement with a non diamagnetic ground state. This kind of temperature dependence

behavior is due to irregular spin state structure. The relative energies of the low-lying

states can be calculated by using obtained exchange coupling constants. The spin state

structure, i.e., the energy versus spin diagram is no longer regular; the spin does not vary

monotonically versus the energy. On the contrary, for J< 0, the ground state has the spin

ST = 2 which is presented schematically in the scheme 2. This irregularity of the spin

state structure has quite drastic consequences on the magnetic behavior. The high-

temperature limit of µeff is equal to the sum of the contributions of the isolated ions.

When the temperature is lowered from high-temperature, the first excited state to be

thermally depopulated and µeff decreases. In the low-temperature range, when only a few

excited states are significantly populated, further cooling depopulates states with a spin

lower than that of the ground state, and µeff increases. At very low temperature, when

only the ground state is populated, µeff reaches a plateau. These high- and low

temperature behaviors result in a minimum for the µeff vs. T plot. The more pronounced

the antiferromagnetic interactions, the higher is the temperature of this minimum.

For a molecule such as 10 with different exchange parameters Jij are

theoretically required for each possible pairwise exchange interactions between

CrIII...CuII, and CrIII...CrIII centers. The exchange parameter between the "wing-tip"

Cr(III) is assumed to be zero given the large distance between Cr(1) and Cr(2) [5.948 Å ].

Inspection of the molecular structure of 10 reveals that there are two main exchange

pathways between the "wing-tip" Cr(III) and "body" Cu(II) centers. The first exchange

pathway JA = J12 = J34 (Jwb) refers to the CrIII(O)(NO)CuII interaction, second one, JB = J14

= J23 (Jwb') refers to the CrIII(NO)CuII interactions. So the magnetic exchange coupling

(JA) between chromium (III) and copper(II) is mediated through different bridges [a two

atom N-O bridge and through oxo bridge], on the other hand the magnetic exchange

coupling (JB) between chromium(III) and copper(II) is mediated through a two atom N-O

bridge. It is to be noted here that the dominated exchange interaction pathways are via the

µ2-OH- groups not the oximate (N-O) transmitters.

TETRANUCLEAR "BUTTERFLY" CORE CONGENERS

CuCu

Cu2

Cr1

Cu4

Cr3

Figure 4.7: Perspective view of coupling scheme. ( JA = J12 = J34 = Jwb, JB = J23 = J14 = Jwb')

Scheme 2

III

So from the magnetochemical view point, only two J values are required: JA = Jwb = J12 =

J34, JB = Jwb' = J14 = J23; where w = wing-tip and b = body. A good fit was obtained with

JA = J12 = J34 = - 79 cm-1; JB = J14 =J23 = - 17 cm-1 with g1 = g3 = 1.98 and g2 = g4 = 2.03.

So, the data for complex 10 was analyzed with a "two-J" model. The higher value of JA

compared to JB can be explained on the basis of spin transmitter. In the model, JA

coupling transmitted through the diatomic N-O bridge and also µ2-hydroxo group while

JB coupling transmitted only through the diatomic N-O bridge. In case of JB the bond

distance between Cr...Cu (4.38Å) is much longer compared to the JA, where Cr...Cu bond

distance is 3.3Å and gives rise to higher interaction in case of JA compared to JB.

CHAPTER 4

50 100 150 200 250 300

3.60

4.05

4.50

4.95

µeff / µB

T/K 0,00,51,01,52,02,5

0,0

0,5

1,0

1,5

2,0

M / Ngß

ßH / kT

1 T

4 T

7 T

Figure 4.8: Magnetic data for CrIII

2CuII

(10) plot of µeff vs T and M/Ngß vs ßH/kT. The bold points

represent the experimental data while the solid line represents the simulation.

The exchange coupling between the chromium(III) and copper(II) is ferromagnetic on the

basis of Goodenough-Kanamori rules. The occurrence of an antiferromagnetic interaction

in 10 is unexpected on the basis of Goodenough-Kanamori rules, since a survey of the

literature,16,35-36,38-39 shows that most generally, the CuII-CrIII pair has a ferromagnetic

interaction with J values ranging from + 1.8 to + 52cm-1(based on H = - 2JSiSj). In these

complexes the equatorial coordination planes are coplanar and ferromagnetism results

from strict orthogonality of the magnetic orbitals. The complex CrIII2CuII2 may adopt a

very low symmetry which could relax the symmetry requirements for effective overlap of

the magnetic orbitals, allowing the AF contribution to be predominant. Moreover the

average Cu-O-Cr angles are 114.5° which reduce the orthogonality of the magnetic

orbitals and can cause a better overlap, gives rise to antiferromagnetic coupling. On the

contrary to the ferromagnetic interaction between CrIII-CuII pair antiferromagnetic spin

interaction J = - 19.5 cm-1 was reported for a CrIII-CuII complex based on oxime ligand.37

Variable temperature variable field magnetic measurements confirm the molar

magnetization (M/Ngß) at 7T, is 1.95, very close to the expected saturation value of ST =

2. The VTVH magnetic measurement was also simulated by using the method of full

matrix diagonalization and from the best fit the values obtained are JA = J12 = J34 = - 79

TETRANUCLEAR "BUTTERFLY" CORE CONGENERS

cm-1, JB = J14 =J23 = - 17 cm-1 with g1 = g3 = 1.98 and g2 = g4 = 2.03. These "J" and g

values are exactly the same values evaluated from the susceptibility measurements at 1 T

described earlier and thus confirm the credibility of the simulated parameters. The

superposition of the variable temperature variable field (VTVH) plots clearly indicates

the absence of zero-field splitting (ZFS or D). So unambiguously the exchange coupling

parameters for this CrIII2CuII2 complex are evaluated

The energy of the ground state ST = 2, has arbitrarily set at zero and which is

42 cm-1 below the first excited state ST = 1, and ST = 0 state is about 67 cm-1 well above

the ground state ST = 2. Since the total spin of the first and the second excited states are

ST = 1 and ST = 0, their population with increasing temperature reduces the effective

magnetic moment of complex 10. Population of the third excited state, ST = 3 occurs

around ∼ 100 K, which accounts for the increase in µeff at higher temperatures. As a result

a minimum is observed in the magnetic moment curve. The ground state with ST = 2

results from spin frustration in a broad sense. The term spin frustration describes as an

effect where the interplay of various exchange interactions in a polynuclear complex

causes a net spin-vector alignment which is different from that expected upon

coordination of pairwise exchange interactions.

Table 4.5: Intratetramer exchange parameters for complexes 9-10

Compounds Magnetic core J12 [cm-1] J23[cm-1] J24[cm-1] gFe gCr gCu(II)

9 FeIII2CuII2J12 = J34

J14 = J23

- 125.0 - 6.0 - 50.0 2.01 2.04

10 CrIII2CuII2J12 = J34

J14 = J23

- 79.0 - 17.0

1.98 2.03

ST = 2

ST = 1

ST = 0

ST = 3

42 cm-1

66 cm-1

336 cm-1

Low-lying states of the CrIII

2CuII

2 complex 10

CHAPTER 4

4.6 References:

(1) W. H. Armstrong, M. E. Roth and S. J. Lippard, J. Am. Chem. Soc., 1987, 109,

6318

(2) J. M. McCusker, J. B. Vincent, E. A. Schmitt, M. L. Mino, K. Shin, D. K.

Coggin, P. M. Hagen, J. C. Huffman, G. Christou and D. N. Hendrickson, J. Am.

Chem. Soc., 1991, 113, 3012

(3) P. Chaudhuri, M. Winter, P. Fleischhauer, W. Hasse, U. Flörke and H. J. Haupt,

Inorg. Chim. Acta., 1993, 212, 241

(4) M. W. Wempel, D. K. Coggin, J. B. Vincent, J. M. McCusker, W. E. Streib, J. C.

Huffman, D. N. Hendrickson and G. Christou, J. Chem. Soc., Dalton Trans., 1998,

719

(5) (a) K. Wieghardt, K. Pohl, I. Jibril and G. Huttner, Angew. Chem. Int. Ed. Engl.,

1984, 23, 77; (b) C. Delfs, D. Gatteschi, L. Pardi, R. Sessoli, K. Wieghardt and D.

Hanke, Inorg Chem., 1993, 32, 3099

(6) (a) V. L Pecoraro, Ed. Manganese Redox Enzymes, VCH verlagsgesellschaft,

Weinheim, 1992; (b) H. Siegel, A. Siegel, Ed. Metal Ions in Biological Systems,

Marcel Dekker, New York, 2000 vol 37

(7) J. B. Vincent, C. Christmas, H-R. Chang, Q. Li, P. D. Boyd, J. C. Huffman, D. N.

Hendrickson and G. Christou, J. Am. Chem. Soc., 1989, 111, 2086

(8) E. Libby, J. M. McCusker, E. A. Schmitt, K. Folting, D. N. Hendrickson and G.

Christou, Inorg. Chem., 1991, 30, 3486

(9) E. Bouwman, M. A. Bolcar, E. Libby, J. C. Huffman, K. Folting and G. Christou,

Inorg Chem., 1992, 31, 5185

(10) M. W. Wempel, H-L. Tsai, S. Wang, J. B. Claude, W. E. Streib, J. C. Huffman,

D. N. Hendrickson and G. Christou, Inorg. Chem., 1996, 35, 6437

(11) P. Chaudhuri, F. Birkelbach, M. Winter, P. Fleischhauer, W. Hasse, U. Flörke

and H-J. Haupt, J. Chem. Soc., Chem. Commun., 1993, 566

(12) P. Chaudhuri, F. Birkelbach, M. Winter; V. Staemmler, P. Fleischhauer; W.

Hasse, U. Flörke and H-J. Haupt, J. Chem. Soc., Dalton Trans., 1994, 2313

(13) P. Chaudhuri, E. Rentschler, F. Birkelbach, C. Krebs, E. Bill, T. Weyhermüller

and U. Flörke, Eur. J. Inorg. Chem., 2003, 541

(14) O. Kahn, Molecular Magnetism, VCH Publishers, Weinheim, 1993

(15) F. Birkelbach, U. Flörke, H-J. Haupt, C. Butzlaff, A. X. Trautwein, K.

Wieghardt, andP. Chaudhuri, Inorg. Chem., 1998, 37, 2000

TETRANUCLEAR "BUTTERFLY" CORE CONGENERS

(16) F. Birkelbach, M. Winter, U. Flörke, H-J. Haupt, C. Butzlaff, M. Lengen, E.

Bill, A. X. Trautwein, K. Wieghardt and P. Chaudhuri, Inorg. Chem., 1994, 33, 3990

(17) C. Krebs, M. Winter, T. Weyhermüller, E. Bill, K. Wieghardt and P. Chaudhuri,

J. Chem. Soc., Chem. Commun., 1995, 1913

(18) P. Chaudhuri, M. Winter; P. Fleischhauer; W. Hasse, U. Flörke andH-J. Haupt,

J. Chem. Soc., Chem. Commun., 1990, 1728

(19) C. N. Verani, E. Rentschler, T. Weyhermüller, E. Bill and P. Chaudhuri, J.

Chem. Soc.,Dalton Trans., 2000, 4263

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Chem. Soc., Chem. Commun., 1998, 2475

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Chaudhuri, Eur. J. Inorg. Chem., 2004, 984

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Chem., 2001, 40, 6656

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Chem. Soc.,Dalton Trans., 2000, 251

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Chem., 1995, 43, 261

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Wieghardt and P. Chaudhuri, J. Chem. Soc.,Dalton Trans., 1997, 4529

(26) A few selected examples: (a) S. Mohanta, K. K. Nanda, L. K. Thompson, U.

Flörke and K. Nag, Inorg. Chem., 1998, 37, 1465; (b) E. Colacio, J. M. Dominguez-

Vera, M. Ghazi, R. Kivekäs, M. Klinga and J. M. Moreno, Inorg. Chem.,1998, 37,

3040; (c) K. E. Vostrikova, D. Luneau, W. Wernsdorfer, P. Rey and M. Verdauger,

J. Am. Chem. Soc., 2000, 122, 718

(27) (a) P. D. W. Boyd, Q. Li, J. B. Vincent, K. Folting, H. R. Chang, W. E. Streib, J.

C. Huffman, G. Christou and D. N. Hendrickson, J. Am. Chem. Soc., 1988, 110,

8537; (b) R. Sessoli, H. L. Tsai, A. R. Schake, S. Wang, J. B. Vincent, K. Folting, D.

Gatteschi, G. Christou and D. N. Hendricson, J. Am. Chem. Soc., 1993, 115, 1804;

A. L Barra, A. Caneschi, A. Cornia, D. Fabrizi de Biani, D. Gatteschi, C.

Sanggregorio, R. Sessoli and L. Sorace, J. Am. Chem. Soc., 1999, 121, 5302

(28) O. Kahn, Chem. Phys. Let., 1997, 265, 109

(29) P. Chaudhuri, Coord. Chem. Rev., 2003, 343, 143

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(30)V. Pavlischuk, F. Birkelbach, T. Weyhermüller, K. Wieghardt and P. Chaudhuri,

Inorg. Chem., 2002, 41, 4405

(31) P. Chaudhuri, M. Winter, H. J. Kuppers, K. Wieghardt, B. Nuber and J. Weiss,

Inorg. Chem., 1987, 26, 3302

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(33) (a) J. B. Goodenough, Phy. Rev 1955, 100, 564; (b) J. Kanamori, J. Phys. Chem.

Solids, 1959, 10, 87

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1077; (b) S. Fox, A. Nanthakumar, M. Wikstrom, K. D. Karlin and N. J. Blackburn,

J. Am. Chem. Soc., 1996, 118, 24; (c) K. D. Karlin, A. Nanthakumar, S. Fox, N. N.

Murthy, N. Ravi, B. H. Huynh, R. D. Orosz and E. P. Day, J. Am. Chem. Soc., 1994,

116, 4753 ; (d) M. J. Scot, H. H. Zhang, S. C. Lee, B. Hedman, K. O. Hodgson and

R. H. Holm, J. Am. Chem. Soc., 1995, 117, 568; (e) S. C. Lee and R. H. Holm, J. Am.

Chem. Soc., 1996, 115, 11789; (f) K. E. Kaufmann, C. A. Goddard, Y. Zang, R. H.

Holm and E. Münck, Inorg. Chem.,1997, 36, 985; (g) H. V. Obias, G. P. F. Van

Strijdonk, D-H. Lee, M. Ralle, N. J. Blackburn and K. D. Karlin, J. Am. Chem. Soc.,

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Chem.,1993, 32, 5385

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Matsumoto, H. Okawa and S. Kida, Inorg. Chem.,1991, 30, 436; (c) Z. J. Zhong, N.

Matsumoto, H. Okawa and S. Kida, Chem. Lett.,1990, 87; (d) Z. J. Zhong, H.

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J. Ulstrup, J. Chem. Soc.,Dalton Trans., 1999, 2675; (b) C. Stadler, J. Daub, J.

Kohler, R. W. Saalfrank, V. Coropceanu, V. Schunemann, C. Ober, A. X. Trautwein,

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Lengen, A. X. Trautwein, E. Bill, K. Wieghardt and P. Chaudhuri, Inorg.

Chem.,1998, 37, 1009

TETRANUCLEAR "BUTTERFLY" CORE CONGENERS

(40) Y. Journaux, O. Kahn, J. Zarembowitch, J. Galy and J. Jaud, J. Am. Chem. Soc.,

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(41) (a) W.E. Marsh, K.C. Patel, W.E. Hatfield and D.J. Hodgson, Inorg. Chem.,

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R. D. Willett. Inorg. Chim. Acta., 1988, 141, 83 and references therein.

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Carrabine and M. Sunderlingam, J. Am. Chem. Soc., 1970, 92, 369; (d) R. F. Drake,

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Dalton Trans., 1984, 1349

CHAPTER 5

STAR SHAPED MnII4 AND TETRAHEDRAL MnIII4 HIGH-SPIN

MOLECULES.

MBMA

5.1 Introduction:

Polynuclear manganese clusters have received considerable interest in recent years. The

interest arises, mainly due to the interesting magnetochemical properties of polynuclear

complexes. One of the focuses in this respect is to achieve molecular systems with high-

spin ground states via intramolecular ferromagnetic coupling or ferromagnetic-like

effects, which are attractive as potential precursors to molecular magnetic materials or as

single-molecule magnets (SMMs).1-4 Another important impetus for investigating

polynuclear Mn clusters lies in their biological relevance. It has become accepted that the

water-oxidizing complex (WOC) of Photosystem II contains a tetranuclear manganese

aggregate, although the structure has not yet been fully understood.5 Thus far, numerous

Mn4 clusters have been reported, the core structure varying from butterfly-like, cubane-

like, adamantane-like, tetrahedral, rhomboidal, linear to "pair-of-dimer", and others.4-7

Surprisingly, the trigonal Mn4 structure with a Mn atom at the center (centered trigonal

cluster) is rare. Although the topology is rather simple and may exhibit interesting

magnetic properties: the ferromagnetic interaction between the central metal ion and the

apical ones would lead to an ST = 10 ground state with the spin structure illustrated in

Scheme 1a, while the antiferromagnetic interaction would lead to an ST = 5 ground state

with the spin structure illustrated in Scheme 1b. A tetranuclear Fe(III) cluster with this

TETRANUCLEAR "HIGH-SPIN" MANGANESE COMPLEXES

simple topology and double methoxo bridges [Fe4(OCH3)6(dpm)6, where Hdpm =

dipivaloylmethane] has been reported to behave as a single-molecule magnet8 in which

the double methoxo bridges mediate antiferromagnetic interaction to give rise to the

expected ST = 5 ground state (Scheme 1b). Herein, the structural and magnetic

characterization of a Mn4 cluster that exhibits this interesting topology will be discussed.

The compound, [Mn4(ppi)6](BF4)2 (Hppi is the Schiff base derived from 2-

pyridylaldehyde and 2-aminophenol), contains the trigonal Mn(II)[(µ2-phenoxo)2Mn(II)]3

cluster core in which very weak ferromagnetic interactions are operative through the

double phenoxo bridges, leading to a ST = 10 ground state not well isolated from other

low-lying states.

Scheme 1

5.2 Synthesis:

Synthetic clusters containing three or four or more metal centers are often obtained by

self assembly reactions. Small variations of the reaction conditions may have a great

influence on the resulting structure. Therefore well directed design is of high interest for

preparative inorganic chemistry to open new ways for the synthesis of polynuclear

complexes. The use of precursor complexes as building blocks establishes an accessible

way to design multinuclear compounds with a defined structural arrangement. The

CHAPTER 5

complex [MnII4(ppi)6](BF4)2 was synthesized by using the precursor complex [Mn(ppi)2],

where [Mn(ppi)2] is the mononuclear neutral MnII complex, in which two ppi ligands

chelate the manganese atom and both the phenoxo oxygen atom occupy the cis position.

In the tetranuclear [MnII4(ppi)6]2+ complex dication Mn(1), Mn(1A) and Mn(3) are

equivalently coordinated by two deprotonated Hppi ligands leading to N4O2 donor set.

The environment of the central Mn(2) is formed by coordination of the three [Mn(ppi)2]

fragments resulting in a phenoxo bridged star-shaped Mn4O6 core motif.

MBMA

Figure 5.1: Perspective view of the star-shaped core motif

The complex [MnIII4(salox)4(salox H)4] was synthesized by using the ligand salicylaldoxime

(saloxH2), MnCl2.4H2O and Et3N in 2:1:4 ratio.

5.3 Infrared and Mass Spectroscopy:

The C=N stretching band in the MnII4 (11) complex is observed at 1585 cm-1, while the

strong Npy stretching band is observed at 1457 cm-1. The bands at 1083 and 1061 cm-1

corresponds to the stretching frequency of B-F, confirms the presence of BF4 anion as the

counteranion in the molecule.

The C=N stretching band in the MnIII4 (12) complex is observed at 1598 cm-1, while the

sharp O-H stretching band is observed at 3422 cm-1 and the band at 2900 cm-1 confirms the

hydrogen bonded OH...O core, which is also evidenced from the single-crystal X-ray

structure. The NO stretchings for the "tetrahedral" MnIII4 complex are observed at 1152 and

1122 cm-1.

TETRANUCLEAR "HIGH-SPIN" MANGANESE COMPLEXES

The manganese containing complex MnII4 (11) provide signals in the ESI mass spectrum

which allow unambiguous characterization of the complex. The base peak at 701 is due to

the dipositively charged species [M-2BF4]2+. The peak due to monocation [M-BF4]+ (10%

intensity) is also observed. Similarly for the MnIII4 (12) complex the peak due to [M-2(salox

H)]+ corresponds to the base peak and the peak due to [MnIII4(salox)4(salox H)4] is also

observed with 10% intensity.

5.4 Solid State Molecular Structure:

5.4.1 Structure of tetranuclear "High Spin Molecule" with a Star-Shaped Mn4O6

core motif (11)

The molecular geometry and atom labeling scheme of the dication are shown in

Figure 5.2. The crystallographic analysis of the complex revealed that the structure of 11

consists of a dicationic tetranuclear Mn(II) cluster with [Mn4(ppi)6]2+, with

tetrafluoroborate ions as counteranions, two acetonitrile molecules and one water

molecule as solvents of crystallization. A perspective view of the cluster is shown in

Figure 5.2 with selected bond distances and angles listed in Table 5.1.

The tetramanganese cluster contains a MnII[(µ2-O)2MnII]3 trigonal core with a Mn

atom (Mn2) at the center and three Mn atoms (Mn1, Mn1A, Mn3) at the apexes and lies

on a crystallographic 2-fold axis that passes through Mn2 and Mn1. Each of the apical

Mn(II) ions is ligated by two deprotonated ppi ligands, which are tridentate via the

pyridyl nitrogen, imine nitrogen, and phenolate oxygen atoms, to complete a highly

distorted octahedral MnN4O2 coordination sphere. Although Mn1 and Mn3 are

crystallographically independent, their bond distances and angles are more or less similar.

As expected, the Mn-N distances [2.214(2)-2.337(2) Å] are longer than the Mn-O

distances [2.138(14)-2.144(14) Å]. The pyridine nitrogen atoms N(1) and N(21) exhibit

the longest distances to Mn(1) [2.288(2)-2.313(2) Å]. The three donor atoms of each

ligand occupy the meridional positions around the metal ion and form two five-

membered chelate rings, imposing very large angular distortions upon the coordination

environments: the N(pyridyl)-Mn-N(azomethine) and O(phenoxo)-Mn-N(azomethine)

bite angles of the ligands are restricted to values smaller than 74°. The bond angles of cis

O(15)-Mn1-N(8), N(8)-Mn(1)-N(1), and O(15)-Mn(1)-N(1) with values 74.26(6)°,

72.14(6)° and 142.33(6)° are indicative of a distortion of the octahedral coordination

CHAPTER 5

environment of Mn(1). This can be attributed to the ligand structure that only allows for

the formation of five membered chelate rings. Despite their conjugated π system, both the

ligands show a distortion from planarity.

All the six ligands in the cluster are further coordinated to the central Mn(2) atom via

their phenolate oxygen atoms, completing a pseudo-octahedral MnO6 coordination

environment around Mn(2), and hence, each apical MnII ion is linked to the central one

through a double phenoxo bridging moiety. The distortion of the Mn(2) sphere is much

less significant than that of the apical MnII spheres. The cis O-Mn(2)-O angles are in the

ranges of 79.81-94.9°, and the trans angles are about 170°. The Mn(2)-O distances fall in

a narrow range of 2.1695(14)-2.186(14) Å and are slightly longer than the Mn(apical)-O

bond distances. Detailed examination of the bond parameters around Mn2 shows the

coordination environment approaches 3-fold symmetry very closely.

The independent double µ2-phenoxo bridging moieties in the cluster show only

minor differences. The Mn-O-Mn, O-Mn(apical)-O, and O-Mn(2)-O angles are in the

narrow ranges of 98.75-100.8°, 79.81-82.40°, and 78.55-80.1°, respectively, while all the

Mn···Mn distances spanned by the phenoxo bridges are equal within experimental error,

taking the value 3.3 Å. The structural parameters are similar to those of [MnII4L6](BPh4)2

and [MnII4L6](ClO4)2 complexes reported recently.37

Figure 5.2: ORTEP and labeling scheme for MnII

4 (11)

TETRANUCLEAR "HIGH-SPIN" MANGANESE COMPLEXES

Due to the presence of the 2-fold axis through the cluster, the four Mn atoms are strictly

coplanar and form a centered isosceles triangle. The apical angle Mn1···Mn3···Mn1A is

61.19°, and the basal and side edge lengths are, respectively, 5.78 Å (Mn1···Mn1A) and

5.68 Å (Mn1···Mn3). The Mn(1)-O(15)-Mn(2)-O(35) bridging ring is strictly planar,

which is imposed by the 2-fold symmetry, and the Mn(2)-O(55)-Mn(3)-O(55)≠ ring is

also planar with the constituent atoms deviating from the mean plane by only ±0.001 Å,

negligible within experimental error. The Mn(2)-O(55)-Mn(3)- O(55)≠ ring forms

dihedral angles of 91.9 and 95.4 with the Mn(2)-O(55)-Mn3-O(35) ≠ and Mn(1)-O(15)-

Mn(2)-O(35) rings, respectively. Therefore, the tetranuclear molecule has a propeller

shape and is chiral. Neighboring molecules are related by rotations to give a heterochiral

but noncentrosymmetric structure. The molecules in the crystal are well separated from

each other with the shortest Mn···Mn distance between neighboring clusters being 10.34

Å.

Table 5.1: Selected Bond Lengths (Å) and Angles (deg) [MnII4(ppi)6](BF4)2 .2CH3CN . H2O

Mn(1)•••Mn(2) 3.286 Mn(3)•••Mn(2) 3.322

Mn(1)-O(15) 2.139(14) Mn(2)-O(55) 2.17(14)

Mn(1)-O(35) 2.144(14) Mn(2)-O(55) 2.17(14)

Mn(1)-N(28) 2.214(2) Mn(2)-O(15) 2.181(14)

Mn(1)-N(8) 2.223(2) Mn(2)-O(15) 2.181(14)

Mn(1)-N(1) 2.288(2) Mn(2)-O(35) 2.186(14)

Mn(1)-N(21) 2.313(2) Mn(2)-O(35) 2.186(14)

Mn(3)-O(55) 2.141(14) N(50)-Mn(3)-N(42) 143.56(11)

Mn(3)-O(55) 2.247(14) N(10)-Mn(1)-N(2) 141.7(12)

Mn(3)-N(48) 2.226(2) O(15)-Mn(1)-O(35) 82.00(5)

Mn(3)-N(48) 2.226(2) O(55)-Mn(3)-O(55) 79.81(8)

Mn(3)-N(41) 2.337(2) O(55)-Mn(2)-O(55) 78.55(7)

Mn(3)-N(41) 2.337(2) O(15)-Mn(2)-O(15) 93.68(8)

O(55)-Mn(2)-O(15) 168.54(5)

Mn(1)-O(15)-Mn(2) 99.07(6)

Mn(1)-O(35)-Mn(2) 98.75(11)

Mn(3)-O(55)-Mn(2) 100.82(6)

CHAPTER 5

Mn(3)-O(55)-Mn(2) 100.82(6)

5.4.2 X-ray Structure of [MnIII4(salox)4 (salox H)4] 2.5 CH3OH (12)

The lattice is built of discrete neutral tetranuclear units and two and half methanol

molecules of crystallization. The molecular geometry and atom labeling scheme of the

tetranuclear unit is shown in Figure 5.3. The tetranuclear unit possesses a tetrahedral

MnIII4 core. The Nox-O bond lengths of average 1.343 +0.003 Å are nearly identical to

those for other comparable structures and significantly shorter than 1.40 Å in general for

free oxime ligands. The bond distance C=Nox (average 1.28Å) are expected, identical for

other reported complexes.

The X-ray crystal structure depicts a cluster containing four MnIII centers, each of which

has a distorted octahedral coordination environment with four O and two cis N donor

atoms. Each MnIII center is ligated by a terminal bidentate saloxH N and O donor [those

containing N(19), N(39), N(59), N(79) and four atoms (1N and 3O) of ligand [[those

containing N(19), N(39), N(59), N(79)] Each of these bridging ligand joins two MnIII

centers through its oximate oxygen atom (µ-O); the attached nitrogen atom links this Mn-

O-Mn moiety to a third MnIII center (µ-ON) and the phenolate oxygen atom is bound to

this MnIII ion to form a six membered MnNCCCO chelate ring. The structure of the

cluster is further stabilized by four intramolecular hydrogen bonds between a terminal

oxime NOH group of the bidentate salox H ligand and the adjacent phenolate oxygen

atom of another such ligand. The X-ray structure clearly shows that all the manganese

ions are Jahn-Teller distorted, high-spin d4 MnIII ions; the axially elongated sites are

occupied by the oximate nitrogen atom and oximate oxygen in µ2-fashion with Mn(1)-

N(19) = 2.261(5)Å, Mn(1)-O(70) = 2.248(4)Å, and O(70)-Mn(1)-N(19) = 168.84(18)°;

Mn(2)-N(39) = 2.276(6)Å, Mn(2)-O(90) = 2.213(5)Å, and O(90)-Mn(2)-N(39) =

166.06(18)°; similarly Mn(3)-N(59) = 2.226(6)Å, Mn(3)-O(30) = 2.232(4)Å , and O(70)-

Mn(3)-N(19) = 166.07(19)° ; Mn(4)-N(19) = 2.261(5)Å, Mn(4)-O(70) = 2.248(4)Å , and

O(70)-Mn(4)-N(19) = 172.26(18)°. Although in oximate based polynuclear systems a two

atom (N-O) bridging group between two metal centers is virtually the universal bonding

mode for oximes, a monoatomic oximate-O bridging is also not very uncommon, and

once again it is also supported from the X-ray structure of the MnIII4 tetrahedron core. All

the oximate oxygen of the ligands are not deprotonated, four oximate oxygen atoms

O(20,40,60,80) remain protonated and hydrogen bonded with the phenolate oxygen atom

TETRANUCLEAR "HIGH-SPIN" MANGANESE COMPLEXES

of the adjacent ligand. The remaining four oximate oxygen atoms O(30,50,70,90) act as a

bifurcated ligands, O(30), O(50), O(70), O(90) act as a bridge between Mn(3) and Mn(2);

Mn(3) and Mn(4); Mn(4) and Mn(1); Mn(1) and Mn(2) respectively. The Mn-Oox bond

lengths lie in the ranges 1.96 to 2.278Å. The average Mn-Ophenoxo bond length is 1.885(4)

Å and is shorter than the Mn-Oox bond distances, whereas the average Mn-N bond length

is 2.135(5)Å. So the metrical parameters for the trivalent manganese ions are significantly

shorter than the metrical parameters of the divalent manganese ions.

The four MnIII centers of the tetranuclear cluster have a distorted tetrahedral arrangement

with average Mn....Mn distances of about 3.5Å for linkage by one µ-O and one µ-ON,

and about 4.1 Å for linkage by two µ-ON groups. A tetranuclear MnIII cluster, albeit with

a different structure, was identified in [L2MnIII2(µ3-O)2(salox)2(µ2-OOCR)3MnIII2](ClO4);

the cation of which contains a butterfly arrangement of the four MnIII centers formed by

two edge sharing MnIII3(µ3-O) triangular units in which deprotonated NO groups bridge

the "wing" and "body" position of manganese atoms.35d A similar isostructural FeIII4

cluster with a tetrahedral core is also known.20

Figure 5.3: ORTEP and labeling scheme for MnIII

4 (12)

CHAPTER 5

There are six strong hydrogen bondings prevailing between the oximate oxygen atoms,

phenoxo oxygen atoms and methanol oxygen atoms and is shown as dotted lines in the

Figure 5.3. The OH...O bond distances lie in the ranges of 2.656-2.889 Å and are listed in

Table 5.2A. These chemically significant hydrogen bondings are responsible for the

stabilization of the tetranuclear core in cluster 12.

Table 5.2: Selected Bond Lengths (Å) and Angles (deg) for [MnIII4(salox)4(salox H)4] 2.5 CH3OH (12)

Mn(1)•••Mn(2) 3.531 Mn(2)•••Mn(3) 3.574

Mn(3)•••Mn(4) 3.578 Mn(4)•••Mn(1) 3.584

Mn(1)-O(21) 1.869(4) Mn(3)-O(61) 1.869(4)

Mn(1)-O(11) 1.900(5) Mn(3)-O(51) 1.901(5)

Mn(1)-O(90) 1.967(4) Mn(3)-O(50) 1.976(4)

Mn(1)-O(70) 2.248(4) Mn(3)-O(30) 2.232(4)

Mn(1)-N(29) 2.035(6) Mn(3)-N(69) 2.022(6)

Mn(1)-N(19) 2.261(5) Mn(3)-N(59) 2.226(6)

Mn(2)-O(41) 1.867(4) Mn(4)-O(81) 1.875(4)

Mn(2)-O(31) 1.912(4) Mn(4)-O(71) 1.896(4)

Mn(2)-O(90) 2.213(5) Mn(4)-O(50) 2.278(5)

Mn(2)-O(30) 1.960(4) Mn(4)-O(70) 1.968(4)

Mn(2)-N(49) 2.012(5) Mn(4)-N(89) 2.009(5)

Mn(2)-N(39) 2.276(6) Mn(4)-N(79) 2.220(6)

O(70)-Mn(1)-N(19) 168.84(18) Mn(2)-O(30)-Mn(3) 116.9(2)

O(90)-Mn(2)-N(39) 166.06(18) Mn(3)-O(50)-Mn(4) 114.4(2)

O(30)-Mn(3)-N(59) 166.07(19) Mn(4)-O(70)-Mn(1) 116.31(18)

O(50)-Mn(4)-N(79) 172.26(18) Mn(1)-O(90)-Mn(2) 114.3(2)

Table 5.1A: Selected Bond Lengths (Å) for the hydrogen bonding in the MnIII

4 cluster.

O(51)•••HO(40) 2.685 O(31)•••HO(20) 2.656

O(81)•••HO(100) 2.889 O(71)•••HO(60) 2.696

TETRANUCLEAR "HIGH-SPIN" MANGANESE COMPLEXES

O(41)•••HO(300) 2.887 O(11)•••HO(80) 2.670

5.5 Magnetic Properties:

5.5.1 Magnetic Properties of MnII4:

The magnetic behavior of MnII4 is shown in Figure 5.4 in the form of the effective

magnetic moments (µeff) versus temperature (T). The magnetic susceptibility was

measured at 1T in the 1.95-290 K temperature range. The magnetic moment of 11.74 µB

(χT = 17.24 emu mol-1 K) at 290 K is lower than the spin only value of χT = 17.5 emu

mol-1 K expected for four isolated high-spin Mn(II) ions. The effective magnetic moment

(µeff) increases monotonically with decreasing temperature until it reaches a value of

12.42 µB (χT = 19.31) emu mol-1 K at 10 K and then starts to decreases and reaches a

value of 7.98 µB (χT = 7.99 emu mol-1 K) at 1.95K. This temperature dependence

magnetic behavior suggests that a ferromagnetic interaction is operative through the

double phenoxo bridges.

To further verify the weak ferromagnetic interaction, variable temperature variable field

(VTVH) measurements have been performed at 1.95 -290K at 1, 4 and 7 T. The molar

magnetizations per MnII4 cluster in the field range of 1, 4 and 7 T are shown in Figure

5.4. When ferromagnetic coupling exists between the central and peripheral Mn(II) ions,

the magnetization will saturate more rapidly than that in the uncoupled system. On the

other hand, if the coupling were antiferromagnetic, the magnetization would increase less

rapidly than that in the uncoupled system. In the present case of 11, the magnetization

increases more rapidly than that of the uncoupled system and saturates at 20Ngβ,

confirming the ferromagnetic interaction

The analysis of the magnetic data was performed using Heisenberg-Dirac-Van

Vleck (HDVV) model. The least squares fitting computer program JULIUS-F with a full

matrix diagonalization approach was employed to fit the temperature and field dependent

magnetization. The program uses the spin-Hamiltonian operator, Htotal = Hz + Hzfs +

HHDVV, where the exchange coupling is described by HHDVV = -2JSi.Sj, the Zeeman

interactions are given by Hz = µBBgiSi and the axial single ion zero field interaction is

described by Hzfs = DSz2. Here we use the Heisenberg spin Hamiltonian in the form E = -

2J(S1S2 + S1S3) - 2J'S1S4 where J = J12 = J13 and J' = J14 .

CHAPTER 5

Mn4

Mn3

Mn1

J14

J13

J12

Schematic representation of exchange coupling model in the star-shaped MnII

4 core

A simulation shown as a solid line in Figure 5.4 results in J = J12 = J13 = + 0.32

cm-1 and J' = J14 = - 0.2 cm-1, with g1 = g2 = g3 =g4 = 1.98. The experimental data can also

be simulated by taking isotropic exchange interactions between the central Mn(2) and the

apical Mn(1,1A, 3) centers with J = J12 = J13 = J14 and the result obtained is J = J12 = J13 =

J14 = + 0.2 cm-1, gMn(II) = 1.98 and θ = - 0.2. But the more physical solution of explaining

the exchange interactions is to consider two different exchange couplings due to the

variation in the average bond angles which are 98.9° [Mn(1)-O-Mn(2); Mn(1A)-O-

Mn(2)] and 100.8°[ Mn(3)-O-Mn(2)]. We have also extracted the exchange coupling

constants by simulating VTVH measurements. The unambiguously determined

parameters are J = J12 = J13 = + 0.47 cm-1 and J' = J14 = - 0.19 cm-1 g1 = g2 = g3 =g4 = 1.98.

So the high-spin Mn(II) centers with S = 5/2 exhibit weak ferromagnetic coupling in the

TETRANUCLEAR "HIGH-SPIN" MANGANESE COMPLEXES

MnII4 molecule as is evidenced from both the magnetic susceptibility and VTVH

measurements, yielding high-spin molecules with ST = 10 ground state.

50 100 150 200 250 300

J12=J13= + 0.32cm-1

J14= - 0.2cm-1

g1=g2=g3=g4=1.98

µeff/µB

T/K

Mn(1)-O-Mn(2)=98.90(av.)

Mn(1)-O-Mn(3)=98.90(av.)

Mn(1)-O-Mn(4)=100.80(av.)

0.0 0.5 1.0 1.5 2.0 2.5

M/Ngß

ßH/kT

4T 7T

Figure 5.4: Magnetic data for MnII

(11) plot of µeff vs T and M/Ngß vs ßH/kT. The bold points represent

the experimental data while the solid line represents the simulation.

So due to the weak exchange coupling between the Mn(II) ions, the molecule exhibits an

extremely complicated low-lying structure which is not well separated from the upper-

lying states, according to the Boltzmann distribution law all the excited states will be

populated. Accordingly, the measured magnetization has more contributions from excited

states of lower spins than from the ground spin. The above discussion is qualitatively

valid, although we have ignored zero-field splitting effects. The negative value suggests

that the zero-field splitting effects should cause a decrease in magnetization, so the

phenomenon that the magnetization of MnII4 increases more rapidly than that of a

hypothetical uncoupled system should be due to ferromagnetic coupling between Mn(II)

ions.

Sofar reported exchange interactions between high-spin Mn(II) ions are weakly

antiferromagnetic, although ferromagnetic coupling between Mn(II) ions is known in one

azide bridge in the -1,1 mode,9 the ferromagnetic coupling between Mn(II) ions mediated

by the phenoxo bridge in 11 is rare. For dimeric Cu(II) or Ni(II) complexes it is well

known that bis(-phenoxo), bis(-alkoxo), and bis(-hydroxo) bridges can mediate overall

antiferromagnetic coupling or, in the case that accidental orthogonality is achieved,

CHAPTER 5

overall ferromagnetic coupling.10-11 Good correlations between the exchange integral J

and the M-O-M bridging angle have been established in case of Ni and Cu, and the

magnetic interaction changes from antiferromagnetic to ferromagnetic at a certain angle

(in most cases around 98°). However, magnetostructural analyses for coupled Mn(II) and

Fe(III) complexes are far more difficult intrinsically due to complications arising from

the larger numbers of magnetic orbitals and exchange pathways that have to be taken into

account for high-spin d5 ions.12-13 Nevertheless, some semiempirical correlations between

J and bridging parameters have been reported for diiron(III) complexes containing -

phenoxo, -alkoxo, or -hydroxo bridges, suggesting that J correlates strongly with Fe-O

distances whereas its dependence on the M-O-M bridging angle is very weak. It is

interesting to note that nearly all these diiron(III) complexes display antiferromagnetic

interactions, and only one has been reported to be ferromagnetic.14 The authors ascribed

ferromagnetic coupling mainly to the distortion of the coordination geometry based on

extended Hückel MO calculations.

The number of oxygen-bridged dimanganese(II) complexes is much smaller than that

of the Fe(III) analogues, probably due to the tendency of Mn(II) to be oxidized. A

number of dimanganese(II) complexes with a phenoxo bridge and one or two other

bridges (frequently carboxylato groups) have been reported,15-16 among which all the

magnetically characterized species were found to exhibit antiferromagnetic

intramolecular interactions with – J < 10 cm-1. For (µ-phenoxo)bis(µ-

carboxylato)dimanganese(II) complexes, Dubois et al. established recently a rough linear

magnetostructural correlation between the J value and the average Mn-O(phenoxo)

distance (dMn-O), and the general trend is - J decreasing as dMn-O increases.16a Some

dimanganese(II) complexes with the bis(µ2-phenoxo), bis(µ2-alkoxo), or bis(µ2-hydroxo)

bridge have also been reported.17-19 While most of them exhibit antiferromagnetic

coupling (- J <10 cm-1) with dMn-O = 2.07-2.16 Å, only a bis(µ2-alkoxo) complex and a

bis(µ2-phenoxo) complex, both with dMn-O = 2.15 Å, have been found to exhibit weak

ferromagnetic interactions (J = + 1.0 and + 0.8 cm-1, respectively).19 In the present

ferromagnetic bis(µ2-phenoxo)-bridged MnII4 complex, the Mn-O distances are between

2.14 and 2.19 Å. Apparently, with these limited data it is impossible to deduce a

correlation between the nature of the coupling and dMn-O for these complexes. We also

compared these complexes in terms of the Mn-O-Mn bridging angle (87-103°) and the

Mn···Mn distance (2.98-3.37Å), and no simple magnetostructural correlation is evident

concerning the nature and magnitude of the magnetic coupling. However, close

TETRANUCLEAR "HIGH-SPIN" MANGANESE COMPLEXES

inspection into structural data reveals that the metal environments in the ferromagnetic

species are highly distorted from octahedral. Similar distortion occurs for the

ferromagnetic bis(µ2-alkoxo)dimanganese(II) complex,19a while the ferromagnetic bis(µ2-

phenoxo)dimanganese(II) complex exhibits more significant distortion: the chelating

carboxylato group dictates a very small cis angle of 55°, and the four largest angles lie in

the narrow 133-140° range.19b It is difficult to distinguish the cis and trans angles in such

a structure. On the other hand, the antiferromagnetic species exhibit relatively small

distortion. The largest distortion was observed for [Mn(SALPS)]2 {SALPS = N,N'-[1,l'-

dithiobis-(phenylene)]bis(salicy1ideneaminato)}18a in which the largest cis and the

smallest trans angles are 108 and 153°, respectively. Although the data available are

limited, the above observation may suggest that the nature of magnetic coupling in this

class of complexes correlates with the distortion of the coordination geometry. Perhaps

the distortion, in conjunction with other factors, dictates a proper relative orientation for

the interacting magnetic orbitals so that accidental orthogonality is achieved.

5.5.2 Magnetic Properties:

Magnetic susceptibility data for polycrystalline samples of the complex 12 were collected

in the temperature range 2-290 K in an applied magnetic field of 1 T. The experimental

data as the effective magnetic moments (µeff) versus temperature (T) are displayed in

Figure 5.5. The experimental magnetic data were simulated using a least squares fitting

computer program with a full-matrix diagonalization approach and the solid lines in

Figures 5.5 represent the simulations.

The analysis of the magnetic data was performed using Heisenberg-Dirac-Van Vleck

(HDVV) model. The least squares fitting computer program JULIUS-F with a full matrix

diagonalization approach was employed to fit the temperature and field dependent

magnetization. The program uses the spin-Hamiltonian operator, Htotal = Hz + Hzfs +

HHDVV, where the exchange coupling is described by HHDVV = -2JS1.S2, the Zeeman

interactions are given by Hz = µBBgiSi and the axial single ion zero field interaction is

described by Hzfs = DSz2.

The magnetic moment µeff/molecule for MnIII4 (12) of 9.82 µB (χM•T = 12.05

cm3•K•mol-1) at 290 K increases monotonically with decreasing temperature until it

reaches a value of 11.58 µB (χM•T = 16.78 cm3•K•mol-1) at 10 K and then starts to

decrease with decreasing temperature and reaches a value of 6.8 µB (χM•T = 5.72

CHAPTER 5

cm3•K•mol-1) at 1.95 K. This temperature dependence is in agreement with

ferromagnetic interaction in the MnIII4 cluster.

The coupling model could probably require two J values, exchange pathways with "edge"

coupling constants and "diagonal" coupling constants; the dominant one would be

expected to be that associated with the Mn(µ-O)Mn fragment, since µ-oxo bridge MnIII

dimers are known to be weakly antiferromagnetic or ferromagnetic in nature.

Mn1

J24

J14

J34

J13

J12

J23

Mn4

Mn3

Mn2

Schematic representation of exchange coupling model in the tetrahedral MnIII

4 core.

Simulations of the experimental data for 12 yield two coupling constants of nearly same

magnitude, but with opposite signs. In the model as shown below, J (J12 = J23 = J34 = J14)

represents the exchange interactions between adjacent metal ions, whereas J'(J13 = J24)

describes interaction between the corner ions of the tetrahedral MnIII4 core. Here we use

the Heisenberg spin Hamiltonian in the form E = - 2J(S1S2 + S2S3 + S3S4 + S1S4) -

TETRANUCLEAR "HIGH-SPIN" MANGANESE COMPLEXES

2J'(S1S3 + S2S4). The J coupling is mediated through a combination of µ2-NO and µ2-

O(N) groups, while the J’ is mediated only through µ2-NO group.

The nearest neighbour coupling i e., the exchange interactions between Mn(1)....Mn(2),

Mn(2)....Mn(3), Mn(3)...Mn(4), Mn(4)....Mn(1) pairs, J is ferromagnetic in nature with a

value of + 1.9 cm-1, but the spin interactions between the diagonal Mn(III) ions,

Mn(1)....Mn(3), Mn(2)....Mn(4) are antiferromagnetic with J' = - 1.6 cm-1. To simulate

the experimental data with an "one-J" model proved to be unsuccessful. To fit particularly

the low temperature data for 12, it is necessary to consider the single ion zero-field

splitting parameter for Mn(III), D(MnIII) during the fitting procedure. It is important to

note that variations of µeff are not very sensitive to the sign of D and it is difficult, if not

impossible, to determine unambiguously the sign of D from powder magnetic

susceptibility measurement. From the best fit the parameters obtained are J = + 1.9 cm-1,

J' = - 1.6 cm-1, ⎢D ⎢= 3.00 cm-1 and gMnIII = 1.95

0.0 0.5 1.0 1.5 2.0 2.5

M/Ngß

ßH/kT

1 T

4 T

7 T

50 100 150 200 250 300

µeff / µB

T/K

Figure 5.5: Magnetic data for MnIII

(12) plot of µeff vs. T and M/Ngß vs. ßH/kT. The bold points

represent the experimental data while the solid line represents the simulation.

To determine the spin ground state, magnetization data were collected at 1, 4 and 7 T in

the temperature range 2-290 K and plotted as reduced magnetization (M/Ngβ) vs.

(βH/kT) (vide infra), where N is the Avogadro’s number, β is the Bohr magneton and k is

the Boltzmann's constant. For a system occupying only the ground state and experiencing

no zero-field splitting (D), the various isofield lines would be superimposed and M/Ngβ

CHAPTER 5

would saturate at a value S. The non-superposition of the variable temperature variable

field (VTVH) plots at low temperature clearly indicates the presence of zero-field

splitting (ZFS or D). Reduced magnetization measurement yielded a ground state ST = 8

Attempts to fit the data by using the method of full-matrix diagonalization of the spin

Hamiltonian matrix including axial ZFS, with the pairwise exchange interactions,

produced best fits with, J = + 1.9 cm-1, J' = - 1.6 cm-1, gMn = 1.95, D1 = D3 = D5 = D6 =

⎢DMn(III) ⎢ = 3.0 cm-1. These "J" and g values are exactly the same values evaluated from

the susceptibility measurements at 1 T described earlier and thus confirm the credibility

of the simulated parameters. The variable temperature variable field (VTVH) plot is

shown in the Figure 5.5. It should be pointed that the main source of the molecular

anisotropy is due to the presence of four Jahn-Teller distorted MnIII ions. The projections

of these single-ion anisotropies onto the molecular anisotropy axis will determine the

molecular parameter D. This above result suggests that unambiguous determination of the

sign of D is not precisely possible from VTVH measurements.

A consideration of intermolecular interactions is relevant to the discussion that follows

of the magnetic properties of this complex. Magnetochemical characterization reveals

that the tetrahedral MnIII4 complex possesses small intramolecular ferromagnetic and

antiferromagnetic interactions manifested through this µ2-NO and µ2-O(N) bridges. The

smaller magnitude of the exchange interactions derived for 12 may result from the fact

that the O-atom bridge is a µ-ON rather than a µ-oxo. It must be stressed again that when

two spin carriers are bridged by several groups, identical or different, it is not possible to

analyze the interaction parameter deduced from magnetic data without taking into

account the phase relations between the bridges. In other terms, what is crucial for

predicting the nature of the interaction is not the symmetry of each of the bridges, but the

symmetry of the bridging network as a whole.

Ferromagnetic interactions between MnIII ions found in a tetranuclear manganese

complex reported by Christou et.al.21 Weak ferromagnetic interaction (J = + 1.9 cm-1)

between MnIII centers are also found in an approximately square MnIII4 clusters reported

by Boskovic et al,22 and in a dinuclear manganese(III) oximate complex reported by

Verani et al.35e

The pertinent point of the magnetic analysis and a survey of the series of MnIII-

polynuclear clusters are given below. It led to the combination of similarly sized

antiferromagnetic and ferromagnetic interactions as shown in Figure 5.5. With the sparse

data presented to date, it is not obvious why the J values have different signs, although it

TETRANUCLEAR "HIGH-SPIN" MANGANESE COMPLEXES

is known, that J can be just positive or just negative. The Mn...Mn separation in these

complexes is in the range from 3.08 to 3.26Å , while the Mn-O-Mn angles vary between

117.9 and 130.9°. Variable temperature magnetic measurement of these complexes

indicate both weakly ferromagnetic and antiferromagnetic interactions between

manganese(III) centers.34(see Table 5.3). Observed weak ferromagnetic exchange

coupling constant in the complex 12 with average Mn-O-Mn angle of 115° is in well

accord. Table 5.4 summarizes magnetic parameters of exchange coupled manganese

oximate complexes.36

Table 5.3: Structural and magnetic properties of MnIII....MnIII core congeners

Compounds Magnetic core

Mn-O-Mn

angle(in deg)

JMn(III)..Mn(III)

[cm-1]

References

[Mn2O(OAc)(tmima)2](ClO4)2 . 2CH3CN MnIII-MnIII 130.9 + 1.33 23

[Mn2O(OAc)(bispicen)2](ClO4)3 MnIII-MnIII 130.8 + 19.5 24

[Mn2O(O2CC6H5)2(N3)2(bpy)2](ClO4)3

CH3CN . 4H2O

MnIII-MnIII 122.0 + 8.8 25

[Mn2O(OAc)2Cl2(bpy)2] MnIII-MnIII 124.3 - 4.1 26

[Mn2O(OAc)2((HB(pz)3)]2 . 4CH3CN MnIII-MnIII 125.1 - 0.2 27

[Mn2O(OAc)2((HB(pz)3)]2 . CH3CN MnIII-MnIII 125.0 - 0.7 27

[Mn2O(OAc)2(tacn)2](ClO4)2MnIII-MnIII 117.9 + 9.0 28

[Mn2O(5-NO2-saldien)] MnIII-MnIII 168.4 - 120.0 29

[Mn2O(OAc)2(Me3Tacn)2](ClO4)2 . H2O MnIII-MnIII 120.9 + 9.0 28

[Mn2O(OAc)(tppn)]2(ClO4)4 . 4CH3CN MnIII-MnIII + 11.0 31

[Mn2O(OAc)(tmip)2](ClO4)2 MnIII-MnIII 124.4 - 0.2 30

[Mn2O(OAc)(ttco)2](PF6)2 MnIII-MnIII 122.2 + 4.6 32

[Mn2O(OAc)(mpepma)2](PF6)2 MnIII-MnIII + 1.0 33

[(Me3Tacn)2Mn4(salox)2(µ3-

O)2(Ph2C(OH)COO)3](ClO4)

MnIII-MnIII 92.8 - 7.73 35d

[(Me3Tacn)2Mn4(salox)2(µ3-

O)2(Ph3CCOO)3](ClO4)

MnIII-MnIII - 6.71 35d

Table 5.4: Magnetic parameters in exchange coupled manganese oximate complexes

Compounds Magnetic core JMn(III)..Mn(III)

[cm-1]

References

[(Me3Tacn)MnIII{(dmg)3MnII}MnIII(Me3Tacn)]

(ClO4)2

MnIII-MnIII - 3.0 35a

[(Me3Tacn)MnIII{(dmg)3MnII}MnIII(Me3Tacn)] MnIII-MnIII + 2.7 35a

CHAPTER 5

(ClO4)2

[(Me3Tacn)MnIII{(dmg)3MnII}MnIII(Me3Tacn)]

(ClO4)2

MnIII-MnIII - 2.8 35a

[Mn3(mcoe)6] (NO3) MnIII-MnIII - 0.6 35b

[Mn3(µ3-O)(bamen)3] (ClO4) MnIII-MnIII + 22.3 35c

[(Me3Tacn)2Mn4(salox)2(µ3-O)2(Ph2C(OH)COO)3](ClO4

)

MnIII-MnIII - 0.47 35d

[(Me3Tacn)2Mn4(salox)2(µ3-O)2(Ph3CCOO)3](ClO4) MnIII-MnIII - 1.63 35d

[(Me3Tacn)MnIIIMnIII(salox)3] MnIII-MnIII + 6.5 35e

It is anticipated that further characterization of the system to determine more precisely

the values of ST and D and to fully elucidate the sign of the ZFS(D), alternating current

susceptibility (AC) measurement or high-frequency EPR (HFEPR) techniques will be

needed.

Verification of the ST = 8 ground state and the sign and magnitudes of ZFS parameters

for complex 12

•

2.5 MeOH needs to obtain by means of high-frequency EPR (HFEPR)

method. This technique is ideally suited for complexes that have appreciable zero-field

splitting and/or an integer spin ground state. Since the microwave energies employed (

100 GHz) are relatively large, it is possible to observe direct transitions between the

zero-field split components of the large spin ground state. HFEPR has been used to

characterize the ground state of several high-spin complexes. An analysis of HFEPR

spectra can give the sign and precise value for the ZFS parameters. In an ideal case, the

spin ground state can be determined by simply counting the number of peaks in the fine

structure, and the zero-field splitting can be evaluated from the spacing between

successive peaks in the structure.

5.6 References:

1. (a) O. Kahn, Molecular Magnetism; VCH: New York, 1993. (b) Magnetism: Molecules

to Materials, J. S. Miller, M. Drillon, Eds. Wiley-VCH: Weinheim, 2002.

2. (a) R. Sessoli, H-L. Tsai, A. R. Schake, S. Wang, J. B. Vincent, K. Folting, D.

Gatteschi, G. Christou, D. N. Hendrickson, J. Am. Chem. Soc. 1993, 115, 1804. (b) R.

Sessoli, D. Gatteschi, A. Caneschi, M. A. Novak, Nature 1993, 365, 141.

3. (a) C. Boskovic, E. K. Brechin, W. E. Streib, K. Folting, J. C. Bollinger, D. N.

Hendrickson and G. Christou, J. Am. Chem. Soc., 2002, 124, 3725 and references therein.

(b) D. J. Price, S. R. Batten, B. Moubaraki and K. S. Murray, J. Chem. Soc., Chem.

Commun. 2002, 762; (c) E. K. Brechin, C. Boskovic, W. Wernsdorfer, J. Yoo, A.

TETRANUCLEAR "HIGH-SPIN" MANGANESE COMPLEXES

Yamaguchi, E. C. Sañudo, T. R. Concolino, A. L. Rheingold, H. Ishimoto, D. N.

Hendrickson and G. Christou, J. Am. Chem. Soc. 2002, 124, 9710

4. (a) E. C. Sañudo, V. A Grillo, M. J. Knapp, J. C. Bollinger, J. C. Huffman, D. N.

Hendrickson, and G. Christou, Inorg. Chem. 2002, 41, 2441 (b) S. M. J. Aubin, N. R.

Dilley, L. Pardi, J. Krzystek, M. W. Wemple, L. C. Brunel, M. B. Maple, G. Christou,

and D. N. Hendrickson, J. Am. Chem. Soc. 1998, 120, 4991 (c) S. M. J Aubin, M. W.

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1996, 118, 7746 (d) S. Wang, M. S. Wemple, H-L. Tsai, K. Folting, J. C. Huffman, K.

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CHAPTER 5

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CHAPTER 5

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44, 677

TETRANUCLEAR "HIGH-SPIN" MANGANESE COMPLEXES

112

CHAPTER 6

0.0 0.5 1.0 1.5 2.0 2.5

M / Ngß

ßH / kT

1 T

4 T

7 T

CHAPTER-6

MIXED-

ALENCE HEXANUCLEAR MANGANESE COMPLEXES

OF [MnII2MnIII4O2]12+ AND HEXANUCLEAR COPPER COMPLEX

OF [CuII3O...H...OCuII3]9+ CORE CONGENERS.

6.1 Introduction:

It has been shown previously that the oxime ligands can connect two transition metal

ions, generating oxime bridged polynuclear complexes. Also the ability of the oxime

functionality to efficiently transmit magnetic coupling has been well documented. A

number of complexes with Cu3O or Cu3OH cores held by peripheral bridging ligands

have been reported.1-4 Synthetic and magnetic properties of high nuclearity (≥ 4)

manganese compounds have been the focus of intense interest of research efforts in

recent years. Impetus for studying the structural and physical properties of this class of

molecules has come from a variety of sources including the need for bioinorganic models

of the polynuclear manganese core in Photosystem II, interest in polynuclear compounds

of iron, manganese, nickel as possible molecular units for the construction of magnetic

materials. Large clusters of this kind also represent a new phase of magnetism that lies

between the simple paramagnetism of isolated molecules and the bulk magnetism of

extended lattices.

With the above areas of interest in mind some groups have synthesized a variety of

polynuclear magnanese complexes and characterized them crystallographically and by

several other physical techniques. Several Mn4 compounds have been prepared, which

HEXANUCLEAR COMPLEXES

exhibit either a "butterfly" or "distorted cubane" structural motif and which form the

basic unit of many of the higher nuclearity assemblies. Discrete complexes containing

more than four metal centers are considerably fewer in number.

Continuous interest in polynuclear oxime based complexes enabled the discover

yet uncommon hexanuclear mixed valence MnIII4MnII2 complexes containing the

structural core [MnIII4MnII2(µ4-O)2]. Hexanuclear compound containing the

[MnII4MnIII2(µ4-O)2]10+ core5 which have ST = 0 ground state is known, but the core in the

fashion [MnIII4MnII2(µ4-O)2]12+ is unusual and thus it's magnetic behavior is of interest

and comparisons of its properties to those of the [MnIII4MnII2(µ4-O)2]12+ core can be

made.

Recent report indicates that the pathway used to obtain polynuclear arrays are

based essentially on the following synthetic strategies: (i) the self-assembly method, (ii)

the use of polynucleating ligands and (iii) the use of "complexes as ligands". On the basis

of these principles, a large variety of polynuclear complexes have been synthesized and

magnetostructurally characterized. So on the basis of the self assembly and using

polydentate oxime two manganese hexanuclear and one copper hexanuclear complexes

were isolated and magnetostructurally characterized.

6.2 Synthesis:

Complexation of the trinuclear precursor [Mn3O(CH3COO)6(H2O)3](CH3COO) by 2,6-

diacetylpyridine dioxime ligand in methanolic solution yields hexanuclear complex

[MnII2MnIII4(µ4-O)2(µ2-OMe)2(dapdo)2(dapdoH)4](ClO4)2 (13) and [MnII2MnIII4(µ4-

O)2(µ2-OH)2(dapdo)2(dapdoH)4](ClO4)2 (14) was synthesized by the complexation of

Mn(ClO4)2 .6H2O by 2,6-diacetylpyridine dioxime where dapdoH2 = 2,6-diacetylpyridine

dioxime. The mechanism likely involves reaction of a [Mn3O]7+ unit of trinuclear

complex to a [Mn3O]6+ species which spontaneously aggregates to 13 and 14 containing

the [Mn6O2]12+ core. On the other hand by using another oxime ligand (b), a hexanuclear

copper (II) complex which is also composed of two CuII3O triangular cores synthetically

and magnetostructurally explored and will be discussed briefly in this chapter. The

different oximes used for these hexanuclear complexes are shown on next page:

CHAPTER 6

Figure 6.1: Ligands used for the hexanuclear complexes, (a) dapdoH2, (b) LH2

6.3 Infrared and Mass Spectroscopy:

The relevant bands in IR spectra of the complex 13 and 14 at 3425 and 2950 cm-1

correspond to the O-H and C-H stretching respectively in the MnIII4MnII2 core. A

moderately intense C=N stretching band for the ligand is observed at 1597 cm-1. A

notable feature of the NO stretching for 13 and 14 are the sharp bands at 1141, 1121 cm-1.

A sharp band around 1052 cm-1 is due to bridging OMe groups. Stretching bands at 624

cm-1 correspond to the ClO4 unit which is the counteranion in all the two hexanuclear

magnanese complexes.

Complexes 15 also shows the C=N stretching band for the ligand at 1628 cm-1.

Moderate peaks at 3421 cm-1 corresponds to the presence of O-H stretching. While the

NO stretching bands for the CuII6 complex are observed at 1121, 1089 cm-1, strong peak

at 1080 is due to the BF4 counteranion.

Electrospray-ionaziation mass spectrometry (ESI-MS) in the positive ion mode has

been proved to be very successful in characterizing the hexanuclear manganese and

copper complexes, which show the dipositively charged species [M-2ClO4]2+ as the base

peak for the hexanuclear manganese complexes (14 and 15), and the tripositively charged

species [M-3BF4]3+ for 15.

6.4 X-ray structure:

6.4.1 Solid State Molecular Structure of [MnII2MnIII4(µ4-O)2(µ2-

OH)2(dapdo)2(dapdoH)4](ClO4)2 .6CH3CN (14) :

The molecular structures of the complexes 13 and 14 are depicted in the Figures 6.3 and

6.4 respectively. Approximately equivalent views are presented to aid comparison. The

labeling schemes are similar but not identical. Selected bond lengths and angles for 14

HEXANUCLEAR COMPLEXES

and 13 are given in full detail in Tables 6.1 and 6.2 respectively. The structure of 14 is

identical with that of 13 except for small differences in ligation for example µ-OH in 14

and µ-OMe in 13, herein molecular structure of the complex 14 will be discussed briefly.

The structure of the complex molecule consists of a discrete dicationic

hexanuclear unit; two noncordinatively bound perchlorate anions and six acetonitrile

molecules as solvents of crystallization. The structure of 14 consists of six Mn atoms

arranged as two "edge-sharing" tetrahedra. At the center of each tetrahedron lies a µ4-O2-

ion. Peripheral ligation includes two dioxime dianions, four dioxime monoanions and two

exogenous methoxide ligands for 13, and two exogenous hydroxide ligands for 14.

Oxidation states for the manganese ions in these hexanuclear complexes are readily

assigned by examining the bond distances in each manganese ion. Many compounds

containing Mn(III) ions exhibit the classic Jahn-Teller distorted geometry expected for a

high-spin d4 ion, making the identification of this oxidation state for manganese

straightforward. All the manganese(III) ions are six coordinate and possess distorted

octahedral geometry. Charge considerations indicate a mixed valence MnIII4MnII2

description and the MnIII centers are assigned as Mn(1), Mn(6), Mn(3) and Mn(5) . The

MnII centers are assigned as central Mn(2) and Mn(4), both the MnII centers being seven

coordinate and are crystallographically equivalent as can be seen in Figure 6.3. As shown

in Table 6.1, the Mn(1)-O(100), Mn(3)-O(100), Mn(3)-O(110) distances are noticeably

shorter by 0.40Å than the Mn(2)-O(100) and Mn(2)-O(110) distances consistent with the

higher oxidation state in Mn(1) and Mn(3). As the core structure can be thought of two

similar triangular MnIII2MnII units joined through µ4-O ligation, only one triangular unit

will be discussed. The MnIII pair [Mn(1) and Mn(3)] are bridged by oximate-O(11) and

through µ4-O(100), whereas the MnIIMnIII pairs [Mn(2) and Mn(3)] and [Mn(2) and

Mn(1)] are bridged by [µ4-O(100) and µ2-OH(110)] and [[µ4-O(100) and oximate-O(31)]

respectively. In each triangular MnIII2MnII unit, the MnIII ions [Mn(1) and Mn(3)] have a

distorted N3O3 coordination sphere, whereas the MnII ion [Mn(2)] has distorted N3O4

ligands mode. The usual coordination number of Mn(II) is 6, and since high-spin Mn(II)

obtains no ligand field stabilization in either octahedral or tetrahedral environment, the

geometry about the Mn is dictated by the ligand constraints. In this case, we observe a

seven-coordinated Mn(II) with close to pentagonal bipyramidal geometry. The average

MnIII-Nox bond distance is 2.245(3)Å, significantly longer than the MnIII-Npy bond

distance of 2.166(3)Å. The average MnIII-Oox distance of 1.938(3) Å is significantly

shorter than the divalent manganese oxygen distances lying in the range 2.1-2.3 Å

CHAPTER 6

(average), whereas the MnIII-O(oxo or hydroxo) bond lengths are also significantly

shorter ([1.875(2)Å] compared to the divalent manganese oxygen distance of 2.247(2)Å.

The Mn(1)-O(100)-Mn(3) bond angle is 109.67(12)°. The X-ray structure clearly shows

that the MnIII ions [Mn(1) and Mn(3)] are Jahn-Teller distorted, high spin d4 ions, the

axially elongated sites are occupied by the imine nitrogen atoms of the oximate, with

Mn(1)-N(2) 2.28(3) Å, Mn(1)-N(10) 2.22(3) Å and N(2)-Mn(1)-N(10) 141.7(12)°, Mn(3)-

N(42) 2.37(3) Å , Mn(3)-N(50) 2.17(3) Å and N(42)-Mn(3)-N(50) 143.56(11)°.

The average MnII-Nox bond distance lies in the range of 2.302(3)- 2.384(3) Å, is longer

than the MnIII-Npy bond distance of 2.313(3) Å. The average MnII-Oox distance of

2.265(2) Å is significantly longer than the MnIII-Oox distances of 1.938(3)Å. The µ4-O-

MnII bond distance 2.247(2) Å is also significantly longer than the average µ4-O-

MnIII[1.944(2)Å] bond distance. The µ2-OH(110) which acts as a bridge between divalent

Mn(2) and trivalent Mn(3), showed that the Mn(2)-O(110) bond distance of 2.203(3)Å is

significantly larger than the Mn(3)-O(110) bond distance of 1.875(2)Å. The Mn(1)-

O(100)-Mn(2), The Mn(3)-O(100)-Mn(2), The Mn(3)-O(110)-Mn(2), bond angles are

116.78(11)°, 98.88(10)°, 102.69(11)° respectively.

In addition to the "edge-sharing tetrahedra" description of the Mn6O2 core, two

alternative ways of describing it can be presented that emphasize the structural

relationship to smaller nuclearity Mn/O units: (i) The Mn6O2 unit can be considered as

two [Mn3O]6+ units, joined together by each of the µ3-O2- atoms becoming µ4 by ligation

to the MnII center of the adjacent Mn3O unit. This also relates to the synthetic procedure

for making complex 14 from[Mn3O]7+, for reduction of the [Mn3O]7+ unit yields the

[Mn3O]6+ core and it could be argued that lowering the average metal oxidation state

increases, the basicity of the µ3-O2- and allows ligation to an additional metal center. The

two [MnIII2MnIIO]6+ units comprising the Mn6O2 core of 14 are conceptually representing

its parentage, are Mn(1,2,3)O(100) and Mn(4,5,6)O(100) or, alternatively

Mn(1,3,4)O(100) and Mn(2,5,6)O(100). (ii) The Mn6O2 core can be considered to contain

the [MnIII2MnII2O2] core of [Mn4O2(OH)(L)2(LH)2]+. This unit possesses a planar Mn4

rhombus with two µ3-O bridge, one above and one below the plane. This unit has been

found within 14 [Mn(1,2,3,4)O(100,100)] or [Mn(5,2,6,4)O(100,100)], and completion of

the Mn6O2 core then requires merely the conversion of the two µ3-O2- to µ4-O2- by

ligation to an additional MnII center. Also it is to be noted that the Mn6O2 core contains

the nonplanar "butterfly" like Mn4O2 unit in complex 14. Such a unit in 14 would be

formed by Mn(1,2,4,6)O(100,100) or Mn(3,2,4,5)O(100,100) with Mn(2,4) representing

HEXANUCLEAR COMPLEXES

the "body" or "backbone" positions and completion of the Mn6O2 again requires

conversion of the two µ3-O2- to µ4-O2- by ligation to an additional MnII sites. Thus, the

planar and butterfly like Mn4O2 units represent the products from two possible ways of

removing two Mn atoms from the Mn6O2 core as shown:

Figure 6.2: Schematic view of the hexamanganese core structure

It should also be noted that the MnIII...MnIII [Mn(1) and Mn(3)] separation in the

[MnIII2MnIIO]6+ triangular unit is 3.122(9)Å, and the MnII...MnIII [Mn(1)...Mn(2),

Mn(3)...Mn(2)] separations are 3.516(9)Å and 3.19(9)Å respectively, whereas the

separation between the MnII...MnII [Mn(2)...Mn(4)] is 3.36(9)Å .

Figure 6.3: ORTEP plot of the dication in complex 14

CHAPTER 6

Table 6.1: Selected Bond Lengths (Å) and Angles (deg) [MnII2MnIII4(µ4-O)2(µ2-

OH)2(dapdo)2(dapdoH)4](ClO4)2 .6CH3CN (14)

Mn(1)•••Mn(2) 3.516 Mn(2)•••Mn(3) 3.1903(9)

Mn(1)•••Mn(3) 3.122 Mn(2)•••Mn(4) 3.36

Mn(1) •••Mn(4)

3.616 Mn(3) •••Mn(4) 3.547

Mn(1)-O(100) 1.875(2) Mn(3)-O(100) 1.944(2)

Mn(1)-O(21) 1.890(3) Mn(3)-O(11) 1.925(3)

Mn(1)-O(31) 1.938(3) Mn(3)-O(110) 1.874(3)

Mn(1)-N(12) 2.163(3) Mn(3)-N(52) 2.149(3)

Mn(1)-N(10) 2.215(3) Mn(3)-N(50) 2.170(3)

Mn(1)-N(2) 2.282(3) Mn(3)-N(42) 2.365(3)

Mn(2)-O(110) 2.203(3) N(50)-Mn(3)-N(42) 143.56(11)

Mn(2)-O(100) 2.247(2) N(10)-Mn(1)-N(2) 141.7(12)

Mn(2)-O(51) 2.265(2) Mn(1)-O(100)-Mn(3) 109.67(12)

Mn(2)-O(100) 2.293(3) Mn(1)-O(100)-Mn(2) 116.78(11)

Mn(2)-N(22) 2.302(3) Mn(3)-O(100)-Mn(2) 98.88(10)

Mn(2)-N(32) 2.313(3) Mn(1)-O(100)-Mn(4) 119.99(12)

Mn(2)-N(30) 2.384(3) Mn(3)-O(100)-Mn(4) 113.39(11)

Mn(2)-O(100)-Mn(4) 95.66(9)

Mn(3)-O(110)-Mn(2) 102.69(11)

6.4.2 Solid State Molecular Structure of [MnII2MnIII4(µ4-O)2(µ2-

OMe)2(dapdo)2(dapdoH)4](ClO4)2 .2C2H5OC2H5 (13) :

The structure of the complex 13 consists of a discrete dicationic hexanuclear unit, two

perchlorate anions and two diethyl ether molecules as solvents of crystallization. The

structure of 13 also consists of six Mn atoms arranged as two "edge-sharing" tetrahedra. The

structure of complex 13 is essentially similar with that of 14 except the difference in ligation

between Mn(3) and Mn(2). In the complex 14 one of the bridging unit is µ2-OH, which is

replaced by µ2-OMe in complex 13. Except this difference the core structure is identical

with that of 14. A view of the dication is shown in the Figure 6.4. Selected bond lengths and

angles are given in Table 6.2.

HEXANUCLEAR COMPLEXES

Figure 6.4: ORTEP plot of the dication in complex 13

Table 6.2: Selected Bond Lengths (Å) and Angles (deg) [MnII2MnIII4(µ4-O)2(µ2-

OMe)2(dapdo)2(dapdoH)4](ClO4)2 .2C2H5OC2H5 (13)

Mn(1)•••Mn(2) 3.477 Mn(2)•••Mn(3) 3.2073(15)

Mn(1)•••Mn(3) 3.1147(13) Mn(2)•••Mn(4) 3.396

Mn(1) •••Mn(4) 3.613 Mn(3) •••Mn(4) 3.554

Mn(1)-O(60) 1.877(2) Mn(3)-O(60) 1.944(3)

Mn(1)-O(21) 1.883(3) Mn(3)-O(11) 1.931(4)

Mn(1)-O(31) 1.938(3) Mn(3)-O(70) 1.876(4)

Mn(1)-N(12) 2.153(4) Mn(3)-N(52) 2.137(4)

Mn(1)-N(10) 2.224(4) Mn(3)-N(50) 2.168(4)

Mn(1)-N(2) 2.283(5) Mn(3)-N(42) 2.385(4)

Mn(2)-O(70) 2.207(3) N(50)-Mn(3)-N(42) 143.4(2)

Mn(2)-O(60) 2.222(2) N(10)-Mn(1)-N(2) 142(2)

Mn(2)-O(51) 2.242(4) Mn(1)-O(60)-Mn(3) 109.2(2)

Mn(2)-O(60) 2.306(3) Mn(1)-O(60)-Mn(2) 115.88(2)

Mn(2)-N(22) 2.288(4) Mn(3)-O(60)-Mn(2) 100.46(14)

CHAPTER 6

Mn(2)-N(32) 2.305(4) Mn(1)-O(100)-Mn(4) 119.1(2)

Mn(2)-N(30) 2.370(4) Mn(3)-O(100)-Mn(4) 113.21(15)

Mn(2)-O(100)-Mn(4) 97.18(13)

Mn(3)-O(70)-Mn(2) 103.2(2)

6.4.3 Solid State Molecular Structure of [CuII6(µ3-O)(µ3-OH)L3(H2O)6](BF4)3 (15)

The lattice is built of discrete hexanuclear trications, three tetrafluoroborate

counteranions. The molecular geometry and atom labeling scheme of the complex 15 is

shown in the Figure 6.5. The hexanuclear CuII cluster consists of two linked [Cu3O]

cores. The metal ions lie at the corners of an equilateral triangle and are at an average

distance of 3.204 Å and 3.235 Å respectively in both the two [Cu3O] core. The association

of two parallel triangular Cu3 species is through two µ3-bridging oxo ligands and three

deprotonated oximate dianion (L2-) moieties. Both the two [Cu3O] units are strongly

hydrogen bonded with the formation of [Cu3O...H...OCu3] core, and the bond distance in

the O...H...O core is 2.518Å. There are two oximate groups in each ligand, one oximate

binds one triangular unit while the other part binds the other trinuclear unit, making the

hexanuclear complex. The Nox-O bond lengths of average 1.34 Å are nearly identical to

those for other comparable structures and significantly shorter than 1.40 Å in general for

free oxime ligands. The bond distance C=Nox (average 1.28Å) are expected, identical for

other reported complexes.54

Each copper ion is five coordinate and has a distorted square pyramidal N2O3

environment. The average Cu-N bond distance is 1.976(3)Å, whereas the average Cu-Oox

bond length is 1.937(2)Å. The average Cu-O (oxo or hydroxo) bond length is 1.919(10)Å.

The fifth position of each copper ion is filled by an apical water molecule and this longer

Cu-O bond length is 2.467(5) Å and is very much similar to the bond distance of the

water molecules ligated to the copper ions in reported compounds. In the [Cu3O] core the

trans N(2)-Cu(1)-O(1) bond angle is 176.86°(10), where as the N(5)-Cu(1)-O(30) bond

angle is 168.68°(9), thus the τ parameter55 for each copper in this trinuclear unit is 0.14

and explains that is in square pyramidal environment, [τ = 0 for ideal square pyramidal

and τ = 1 for ideal trigonal bipyramidal geometry]. Similarly in the other [Cu3O] core the

trans N(17)-Cu(2)-O(8) bond angle is 169.17°(15), whereas the N(14)-Cu(2)-O(40) bond

angle is 166.37°(10), thus the τ parameter for each copper in this trinuclear unit is 0.045

HEXANUCLEAR COMPLEXES

and is in a nearly ideal square pyramidal environment. The CuII6 unit can be thought of as

dimer of CuII3 units.

Figure 6.5: ORTEP plot of the trication in complex 15

Three different kinds of non-bonded Cu...Cu separation (3.686Å, 4.239Å, 5.042Å) in the

inter dimer unit is observed, whereas the observed Cu-O-Cu angles in each triangular unit

are 113.65(9)° and 114.32(8)° respectively. The core structure of the hexacopper(II)

cluster is shown below in Figure 6.5A.

CHAPTER 6

Cu2

Cu1

Cu3

Cu4

Cu5

Cu6

Figure 6.5A: Core structure of the hexacopper(II) cluster 15

Table 6.3: Selected Bond Lengths (Å) and Angles (deg) [CuII6(µ3-O)(µ3-OH)L3(H2O)6](BF4)3 (15)

Cu(1)•••Cu(1) 3.204 Cu(2)•••Cu(2) 3.235

Cu(1)•••Cu(2) 3.686 Cu(1)•••Cu(2B) 5,042

Cu(1)•••Cu(2A) 4.239 O(30)...HO(40) 2.518

Cu(1)-O(30) 1.9138(10) Cu(2)-O(40) 1.9251(10)

Cu(1)-O(1) 1.937(2) Cu(2)-O(18) 1.943(3)

Cu(1)-N(2) 1.967(3) Cu(1)-N(17) 1.968(3)

Cu(1)-N(5) 1.999(3) Cu(1)-N(14) 1.989(3)

Cu(1)-O(60) 2.469(5) Cu(1)-O(70) 2.465(5)

Cu(1)-O(30)-Cu(1) 113.65(9) Cu(1)-O(30)-Cu(1) 114.32(8)

N(2)-Cu(1)-O(1) 176.86(10) N(17)-Cu(1)-O(18) 169.17(15)

N(5)-Cu(1)-O(30) 168.68(9) N(14)-Cu(1)-O(40) 166.37(10)

HEXANUCLEAR COMPLEXES

6.5 Magnetic Properties:

6.5.1 Magnetic Properties of Hexanuclear Manganese Complexes

Magnetic susceptibility data for polycrystalline samples of the complexes were collected

in the temperature range 2-290 K in an applied magnetic field of 1T. The Heisenberg spin

Hamiltonian in the form H = -2JA(S1S3 + S5S6) - 2JB (S1S2 + S4S6) - 2JC(S2S3+S4S5)-

2JDS2S4 (for complexes 13 and 14) for an isotropic exchange coupling with S1 = S3 = S5 =

S6 = SMn(III) = 4/2, S2 = S4 = SMn(II) = 5/2 for 13 and 14 are employed to analyze the

magnetic properties. The experimental data as the effective magnetic moments (µeff)

versus temperature (T) are displayed in Figure 6.7. Due to the similarity of the magnetic

nature in complexes 13 and 14, herein detailed magnetism of the complex 14 will be

described in the following section.

The magnetic moment µeff/molecule for 14, MnIII4MnII2, of 11.44 µB (χM•T =

16.35 cm3•K•mol-1) at 290 K is less than expected for the spin only value of χM•T =

20.75 cm3•K•mol-1for 4 uncoupled MnIII and 2 MnII ions and decreases monotonically

with decreasing temperature until it reaches a value of 8.77 µB (χM•T = 9.63 cm3•K•mol-

1) at 30 K and then starts to increase with decreasing temperature and reaches a value of

9.03 µB (χM•T = 10.19 cm3•K•mol-1) at 10 K and then again decreases to reach a value of

6.93µB (χM•T = 5.99 cm3•K•mol-1) at 1.95 K. This temperature dependence behavior is

consistent with the presence of antiferromagnetic interactions between the spin carriers,

with the low temperature value of µeff indicating that the molecule has a reasonably large

spin ground state.

The magnetic moment µeff/molecule for 13, MnIII4MnII2, of 11.34 µB (χM•T = 16.08

cm3•K•mol-1) at 290 K decreases monotonically with decreasing temperature until it

reaches a value of 8.68 µB (χM•T = 9.42 cm3•K•mol-1) at 30 K and then starts to increase

with decreasing temperature and reaches a value of 8.83 µB (χM•T = 9.73 cm3•K•mol-1)

at 10 K and then again decreases to reach a value of 6.76µB (χM•T = 5.72 cm3•K•mol-1)

at 1.95 K.

By far the commonest way to model exchange coupling have been performed

through Kambe's vector coupling method30 and various extensions of Kambe's method

have been used in specific cases. The Heisenberg Hamiltonian, H = - 2J ∑Si Sj can be

expressed in case of n number of paramagnetic spin carriers as equation,

H = - 2 ∑ Jij Si Sj ......(1).

CHAPTER 6

Substitution of the vector model into equation (1) as a general case has been given by the

equation, H = - 2 (∑ Jij Si Sj + 2 ∑ Jin Si Sn + 2 Si Sn)........(2).

The eigen value equation from (2) can be written as: E(ST) = - ∑ (Jij - Jin) [Sij (Sij + 1) -Si

(Si + 1) - Sj (Sj + 1)] - ∑ (Jij - J1n) [Sin (Sin + 1) -Si (Si + 1) - Sn (Sn + 1)] - J1n ST (ST + 1) +

J1n ∑ Si (Si + 1)................(3).

In real situation, suitable simplifications of the problem can often be made from

symmetry considerations in order to reduce equation (3) to an unambiguous and simple

expression, from which the energy values of the spin states will be available and hence

the magnetic susceptibility are readily obtained. However, in completely general case

(none of the Jij necessarily equal) not all the allowed values can be given unambiguously,

and the problem can not be solved by the extended Kambe’s approach. So except for very

specialized cases, exchange interactions in a discrete trinuclear and tetranuclear clusters

can not be described by the Kambe's method of vector coupling. Thus, difficulties

increase as the number of interacting paramagnetic atoms increases. When the number of

paramagnetic centers are greater than 5, suitable equation for E(ST) can be obtained by

substituting in equation (3), but again, for nearly all physical probable arrangement of

paramagnetic atoms. So due to the complexity in polynuclear complexes, Kambe's theory

can not be applied to the general case and it is therefore desirable to evolve a completely

general treatment which would permit complete freedom of choice in the magnitudes of

the exchange integrals of Jij between pair of spins Si and Sj; where none of the Jij or Si, Sj

need to be equal.

The total degeneracy of the spin levels for a cluster of n identical spins S is (2S + 1)n, a

number which grows very fast beyond the possibilities of handling with any computer. It

is apparent that procedures are required which employ symmetry in order to reduce the

dimensions of the matrices. These are essentially of two types, one which takes

advantages of the total spin symmetry and the other which exploits the point symmetry of

the cluster.

A theoretical model to interpret the magnetic susceptibility data for complexes 13 and 14

was sought. At the outset it has to be realized that this is a formidable task, for with four

MnIII (S = 2) and two MnII (S = 5/2) ions, there is a total degeneracy of (2SMnIII + 1)4

(2SMnII + 1)2 = 22400. It is simple to realize that as a result of magnetic interactions, the

hexanuclear complexes have total spin (ST) values of the resultant states range from13,

12, 11,....., 0. So owing to the size and symmetry of the hexamanganese clusters, it is not

possible to use Kambe approach to derive a theoretical equation to fit the χMT versus T

HEXANUCLEAR COMPLEXES

data. In addition this large number of spin states makes it effectively impossible to

evaluate the pairwise exchange interactions in the spin Hamiltonian. However, it takes an

appreciate amount of time with a computer program employing the mathematical

treatment given below to identify all of the 22400 different electronic states for the

hexanuclear manganese complexes. By using irreducible tensor operator (ITO) approach

it is possible to drastically cut the requirement of memory storage and time needed for the

diagonalization of the Hamiltonian matrices, making the calculations for medium size

clusters possible even for work station type computers. So the exchange coupling model

was considered for simulation of the experimental magnetic data using the irreducible

tensor operator (ITO) mathematical method58 with the Heisenberg Hamiltonian in the

form H = - 2JSiSj

An examination of the structures of 13 and 14 shows that two central bis (µ-oxide)-

bridged MnII (S = 5/2) ions are bridged to four MnIII (S = 2) via single µ-oxide bridges.

The bridging pathways connecting each of the MnII ions, Mn(2) or Mn(4), to one pair of

the MnIII ions, Mn(1,3) or Mn(5,6) are equivalent. The appropriate bridging angles in the

structure of 13 and 14 are noticeably different, e.g., Mn(2)-O(100)-Mn(1) and Mn(2)-

O(100)-Mn(3) are 115.88 and 100.46° respectively for 13 and Mn(2)-O(100)-Mn(1) and

Mn(2)-O(100)-Mn(3) are 116.78 and 98.88° respectively. At the same time there is

another µ2-OMe and µ2-OH bridge between the Mn(2) and Mn(3) ions respectively for 13

and 14, giving the Mn(2)-O(110)-Mn(3) angle around 103.2° and102.69° respectively. A

general spin-spin interaction model allowing for dissimilar coupling between the MnII-

MnIII pairs could not be constructed by using the Kambe vector coupling method.

To simplify the problem, a "three-J" model was taken into consideration and the

assumption was made that all of the MnII-MnIII exchange interactions are equal; i.e the

Mn6O2 core has the idealized symmetry (D2h) of the two "edge-sharing" tetrahedra. Least

squares computer program was used to fit the observed temperature dependence of µeff /

Mn6 cluster as a function of the three exchange parameters, J1, J2, J3, and an isotropic g

value. A proposed model for the exchange interactions in the MnIII4MnII2 cluster is shown

below in the scheme 1 and we used the spin Hamiltonian in the form, H = - 2J1(S1S3 +

S5S6) - 2J2(S1S2 + S2S3 + S5S4 + S6S4) - 2J3S2S4; where S1 = S3 = S5 = S6 = 2 and S2 = S4

= 5/2

CHAPTER 6

S3S2S6

S4S5

Scheme 1

During the fitting, it was observed that there was little correlation between the nature of the

experimental susceptibility plot and the simulated curve. In this procedure the simulation

does not show any minimum, which is observed in the experimental data at the lower

temperature region. Possible reasons for this deviation include the neglect of single ion zero-

field splitting or the assumption that all the MnIII..MnII interactions are equal. To test the

latter possibility a "four J" model was employed to fit the experimental data instead of the

"three J" model. A schematic view of the spin topology of the cluster is given below in

scheme 2.

S3S2S6

S4S5

Scheme 2

We used the spin Hamiltonian in the form, H = - 2J1(S1S3 + S5S6) - 2J2(S1S2 + S6S4) - 2J3

(S2S3 + S5S4) - 2J4S2S4; where S1 = S3 = S5 = S6 = 2 and S2 = S4 = 5/2. Since the value of the

parameter g is best determined by the high-temperature data, only the data above 20 K were

fit at first, and by doing so from the best fit the parameters obtained are g = 1.98, J1 = - 12.6

cm-1, J2 = - 4.6 cm-1, J3 = + 2.4 cm-1 and J4 = + 1.9 cm-1. From this simulation the nature of

the curve is similar to that of the experimental one but below 20 K the simulated curve does

not fit perfectly with the experimental one. Zero field splitting effects are likely to influence

the data in this temperature range. The parameter J1 represents the coupling constant

between the Mn(III) atoms, the coupling between Mn(II) and Mn(III) atoms in each

triangular unit are labeled with J2 and J3, while J4 represents the coupling between the Mn(II)

atoms. The µ4-oxo bridges are assumed to be the dominant pathways of magnetic exchange

HEXANUCLEAR COMPLEXES

interactions between the Mn ions. Although the oximate (N-O) and µ2-OH or µ2-OMe

ligands could theoretically transmit the exchange coupling, the fact that the magnetic data

are nearly similar for complexes 13 and 14 support the assumption that the µ4-oxo bridges

dominate the exchange interactions. The values of the MnIII-MnIII, MnII-MnIII and MnII-MnII

exchange coupling parameters can be compared with those found for the oxo-bridged

manganese complexes5-6,8-10,20,22,24-26,29,31-38,41 with attention towards the exchange coupling,

which is mediated through oximate(=N-O) also.29,54,59-60 Interaction through the oximate

bridge are antiferromagnetic in nature as usually observed. The exchange coupling between

the MnII-MnIII pair is weak, in case of J3 the weak ferromagnetic coupling between the

mixed valence manganese ions compared to the weak antiferrmagnetic exchange interaction

(J2) between another set of mixed valence manganese ions can be explained in terms of the

Mn-O-Mn bond angles. The J2 coupling mediates through the Mn-O-Mn angle of 116.78°,

whereas the J3 exchange coupling mediates through average Mn-O-Mn angle of 101.7°,

means, a better overlap between the magnetic orbitals expected in case of J2 and can give

rise to better antiferromagnetic exchange interactions compared to J3. The system may be

envisaged as ferromagnetically coupled two AF triangles and the fact J1>>J3 clearly

stabilizes a local S = 5/2 ground state in each triangular unit. The ferromagnetic pathway (J4)

leads to an S = 5 ground state of the hexanuclear cluster (vide infra). From the above data set

for the exchange coupling constant, it has been observed that ST = 5 has minimum energy

compared to other possible spin states and being the ground state. Similar weak

ferromagnetic exchange coupling constant for MnII(µ4-O)MnII was found in a oximate based

manganese complex reported recently.60a Mn(II)...Mn(II) exchange coupling constant

mediated through µ4-O, with a Mn-O-Mn angle of 94.4° is reported to be + 2.5 cm-1.

Similarly exchange interaction between MnIII centers with a combination of µ3-O and

oximate (N-O) bridge is reported to be - 12.6 cm-1 in a hexanuclear manganese complex.10

In order to provide a theoretical basis for the observed magnetic properties of the complexes

13 and 14, especially to offer a rationale for the high-spin ground state ST = 5 the proposed

model for the exchange interactions in the MnIII4MnII2 clusters, schematic view of the spin

topology is given below.

CHAPTER 6

Mn6

Mn5

Mn1

Mn3

Mn2

Mn4

S = 2 S = 5/2

Figure 6.6: Spin coupling model for the MnII

2MnIII

4 clusters

Detailed rationale of the exchange interaction of the different spin carriers will be given

and compared with the reported literature. The sign of the intramolecular exchange

coupling constant results from the sum of antiferromagnetic and ferromagnetic

contributions given in the equation J = JAF + JF. From the structures of the hexanuclear

clusters the MnIII2O unit in both complexes may be described as resulting from two

octahedrally coordinated manganese(III) ions sharing an edge comprised of a µ-oxo

bridge. The manganese(III) centers (high spin, d4) are tetragonally distorted as is

evidenced in the X-ray structure, the electronic configuration of the localized metal

orbitals being (dxz, dyz)2, (dxy)1, (dz2)1, (dx2-y2)0 in order of increasing energy. It is then

obvious that the interaction between the (dxz, dyz)2 orbitals of the two manganese(III) ions

and the bridging oxygen atom provide antiferromagnetic π-pathways; similarly

HEXANUCLEAR COMPLEXES

antiferromagnetic σ-paths are available between the (dxy)1 pairs via s and p orbitals of

oxygen. The path dz2 ⎢⎢ dz2 involves weakly delocalized in the molecular plane, and its

contribution is expected to be rather weak, irrespective of its magnetic nature, with Mn-O

overlap being of the σ-type. As the MnIII-O-MnIII angle is about 110°, dz2 electrons

interact via an antiferromagnetic pathway involving a non-orthogonality of the bridging

oxygen atom. A negetive J i.e., a net antiferromagnetic interaction is thus expected and is

observed.5-6,9-10,20,22,24-26,29,31-32,35-38,41 This picture is consistent with the predictions made

by Kahn for dinuclear complexes. When MnIII-O-MnIII angle is close to 90°, a

ferromagnetic exchange interaction is also observed.8,24-25,33-34

The MnII...MnIII interactions obtained in this work for complexes 13 and 14 are weakly

antiferromagnetic as have been found in most molecules, that have been reported to have

such interactions. Taking literature data into account the calculated J value (JMnII..MnIII) is

reasonable. The sign and the strength of the exchange interaction between the MnIII

centers in compounds containing the {MnIII2(µ-OR)}4+ subunit, where the oxygen atoms

occupy Jahn-Teller positions at each metal ion, are influenced by subtle geometric and

electronic factors which create a subtle balance between different exchange pathways, as

predicted by Goodenough and Kanamori. One important point is that the complex34

[MnIII2(µ2-O)(µ-O2CR)2(Me3Tacn)2]2+ exhibits ferromagnetic exchange interaction (J = +

9 cm-1) between the MnIII centers. Chaudhuri56 et al., showed the terminal ligand has a

significant effect on the sign and magnitude of J. Recently Solomon et. al showed25 such

a influence on the sign and magnitude of J, e.g, replacement of the terminal ligand

Me3Tacn by bpy and H2O in one complex and bpy and azide in another complex with the

core of [MnIII2(µ2-O)(µ-O2CR)2(bpy)2(H2O)2]2+ and [MnIII2(µ2-O)(µ-O2CR)2(bpy)2(N3)]2+

the value of the exchange coupling constant shifts to - 3.4 cm-1 and + 8.8 cm-1

respectively. Careful study of the literatures8, 24, 27, and 33 reveals that the MnIII-O(R)-MnIII

angles smaller than ≈ 102° tend to favor weak ferromagnetic exchange interactions. Thus

from the viewpoint of this structural parameter only, the antiferromagnetic nature of J1 in

complexes 13 and 14 with MnIII-O(R)-MnIII angle of 110° is understandable whereas the

interaction between MnIII(3) and MnII(2) is also expected to be weak whatever in nature

taking into account all the cross interaction between the said spin carriers and from the

viewpoint of the structural parameter with average MnIII(3)-O(R)-MnII(2) angle of

100.5°, a weak positive exchange coupling constant is more likely. Although there is no

magnetostructural correlations between the MnIII-O-MnII angle and the sign/magnitude of

the exchange constant, it has been shown that for MnIII-O-MnII angle of ≈ 120° the

CHAPTER 6

interaction is antiferromagnetic,5-6,9-10,12-15,17-21,26,31-32,35,38,41 while for ≈ 105° the

interaction is ferromagnetic.5,11,16-19,21,33,39-40 The ferromagnetic nature of exchange

coupling interactions can be explained by assuming prevalent eg-eg contributions. Given

the elongated nature of the distortion from octahedral symmetry, the dx2-y2 orbital is

empty. Due to the arrangement of local elongation axes in the structure, the dz2 magnetic

orbitals of MnIII have a nonzero overlap with the half-filled dx2-y2 orbitals of the MnII

through µ2-OH or µ2-OMe ligands.

50 100 150 200 250 300

µeff / µB

T/K

Figure 6.7: Magnetic data for MnIII

4MnII

(14), plot of µeff vs. T. The bold points represent the

experimental data while the solid line represents the simulation

The weak interaction found between MnIII(3) and MnII(2) may be rationalized on the

basis of the empty dx2-y2 orbital of the MnIII ions and due to the elongated Jahn-Teller

distortion, the electronic configuration of the metal orbitals being (dxz, dyz)2, (dxy)1, (dz2)1,

(dx2-y2)0 in order of increasing energy and presumably the different cross interactions

between the Mn(II) and Mn(III) orbitals cancels each other, and can be anticipated from J

= JAF + JF. This dx2-y2 ⎜⎜ dz2 pathway is expected to provide a ferromagnetic contribution

towards overall exchange coupling constant and is nicely explained by Ginsberg. Thus

the observed exchange coupling constant (J3 = + 2.4 cm-1) is well justified. On the

contrary the MnIII(1)-O(R)-MnII(2) angle of 116° leads to a better overlap between the

magnetic orbitals giving rise to a net weak antiferromagnetic exchange interaction (J2)

HEXANUCLEAR COMPLEXES

and the obtained value in this case is quite reasonable enough. This is consistent with the

literature values reported for binuclear and polynuclear transition metal complexes

containing MnII and MnIII ions

To determine the spin ground state, magnetization data were collected at 1, 4

and 7 T in the temperature range 2-290 K and plotted as reduced magnetization (M/Ngβ)

vs. (βH/kT) (vide infra), where N is the Avogadro’s number, β is the Bohr magneton and

k is the Boltzmann's constant. For a system occupying only the ground state and

experiencing no zero-field splitting (D), the various isofield lines would be superimposed

and M/Ngβ would saturate at a value S. The non-superposition of the variable

temperature variable field (VTVH) plots at low temperature clearly indicates the presence

of zero-field splitting (ZFS or D). Reduced magnetization measurement yielded a ground

state ST = 5.

Attempts to fit the data by using the method of full-matrix diagonalization of

the spin Hamiltonian matrix including axial ZFS, with the pairwise exchange interactions,

produced best fits with, J1 = - 12.6 cm-1, J2 = - 4.6 cm-1, J3 = + 2.4 cm-1, J4 = + 1.9 cm-1,

gMn = 1.98, D1 = D3 = D5 = D6 = DMn(III) = 4.0 cm-1. These "J" and g values are exactly the

same values evaluated from the susceptibility measurements at 1 T described earlier and

thus confirm the credibility of the simulated parameters. The variable temperature

variable field (VTVH) plot is shown in the Figure 6.8. It should be pointed that the main

source of the molecular anisotropy is due to the presence of four Jahn-Teller distorted

MnIII ions. The projections of these single-ion anisotropies onto the molecular anisotropy

axis will determine the molecular parameter D. With D1 = D3 = D5 = D6 = DMn(III) = - 4.0

cm-1 a fit of poorer quality than that with positive D was obtained.

It is anticipated that further characterization of the system to determine more precisely

the values of ST and D and to fully elucidate the sign of the ZFS(D), alternating current

susceptibility (AC) measurement or high-frequency EPR (HFEPR) techniques will be

needed.

CHAPTER 6

0.0 0.5 1.0 1.5 2.0 2.5

M / Ngß

ßH / kT

1 T

4 T

7 T

Figure 6.8: Variable temperature variable field (VTVH) magnetic data for MnIII

4MnII

(14), plot of

M/Ngß vs. ßH/kT. The bold points represent the experimental data while the solid line represents the

simulation

In order to offer a rationale for the high-spin ground-state where ferromagnetically

coupled two AF [MnIII2MnII] triangular units give rise to ST = 5 ground state is shown

below in Figure 6.9

Mn Mn

Mn F

J2J2

Mn Mn

J2J2

Figure 6.9: Pictorial representation of exchange coupling for the two possibilities for the ground states,

the above diagram shows the ST = 5 ground state (above) and ST = 0 ground state (below).

HEXANUCLEAR COMPLEXES

The main lesson from these study is that high nuclearity Mnx complexes can be

prepared which have either pairwise ferromagnetic MnII...MnIII or MnIII...MnIII

interactions or a combination of pairwise antiferromagnetic interactions or in the third

possibility a combination of pairwise ferromagnetic-antiferromagnetic interactions that

lead to molecules with ST ≠ 0 ground state. Combinations of pairwise exchange

interactions or competing exchange interactions and topology stabilize the high spin

ground states of these polynuclear manganese complexes.

Although no simple straightforward magnetostructural correlation has been

established based on either Mn....Mn separation or Mn-O-Mn angles (except in case of J

vs MnIV-O-MnIV),57 with the availability of more structural data for closely related

complexes displaying suitable variation over the structural parameters, qualitative

magnetostructural correlations for exchange coupling in manganese complexes can be

provided. But based on Goodenough-Kanamori, Ginsberg42 and Kahn7 it can be

concluded that MnII...MnIII and MnIII...MnIII interactions are weakly ferromagnetic or

weakly antiferromagnetic in nature depending on the Mn-O-Mn angle, when it is close to

90°, orthogonality of the magnetic orbitals would be expected and thus provides

ferromagnetic exchange, while deviations from 90°, causes the net exchange interaction

to be antiferromagnetic.

6.5.2 Magnetic Properties of CuII6:

Magnetic susceptibility data for polycrystalline samples of the complexes were collected

in the temperature range 2-290 K in an applied magnetic field of 1 T. The experimental

data as the effective magnetic moments (µeff) versus temperature (T) are displayed in

Figure 6.10. The experimental magnetic data were simulated using a least squares fitting

computer program with a full-matrix diagonalization approach and the solid lines in the

Figure 6.10 represent the simulations. The magnetic moment µeff/molecule for 15, CuII6,

of 2.77 µB (χM•T = 0.96cm3•K•mol-1) at 290 K is smaller than the value of six uncoupled

copper (II) ions (χM•T = 2.25 cm3•K•mol-1) assuming g = 2.00 and decreases

monotonically with decreasing temperature until it reaches a value of 1.65 µB (χM•T =

0.34 cm3•K•mol-1) at 1.9 K . This temperature dependence is in agreement with a strong

antiferromagnetic exchange interaction between the spin carriers.[CuII6(O)2]8+ core has a

strong antiferromagnetic interaction within both the [Cu3O]4+ subunit and leaves a single

unpaired electron in each triangular unit. If the trimeric unit has each metal equivalent

CHAPTER 6

and forms an equilateral triangle the spin Hamiltonian will describe in the form given as,

H = -2JA(S1S2 + S1S3 + S2S3 + S4S5 + S4S6 + S6S5) for an isotropic exchange coupling

with S1 S

2 = S3 = S4 = S5 = S6 = SCu(II) = 1/2. But for a better model the exchange

interaction between the interdimer units was taken into consideration and hence by using

a "two J" model the magnetic data of the hexacopper complex was analyzed and we used

the Hamiltonian in the form; H = -2JA(S1S2 + S1S3 + S2S3 + S4S5 + S4S6 + S6S5) - 2JB(S1S4

+ S1S5 + S1S6 + S2S4 + S2S5 + S2S6 + S3S4 + S3S5 + S3S6)

50 100 150 200 250 300

1.0

1.5

2.0

2.5

3.0

µeff / µB

T/K

Figure 6.10: Magnetic data for CuII

(16), plot of µeff vs. T. The square points represent the experimental

data while the solid line represents the simulation

So the magnetic susceptibility data was simulated by full matrix diagonalization of the

appropriate isotropic spin Hamiltonian for a CuII6 molecule with a dimer of trimers

topology. The fit was carried out by the Irreducible Tensor Operator (ITO) formalism

using the CLUMAG program and provides best fit with the following parameters : JA = -

614.0 cm-1, JB = - 114.5 cm-1 and g = 2.00.

As previously reported43-48 the strong antiferromagnetic coupling is possible when the

trinuclear entity is completely planar. The triangular Cu3X (X = OH, O) core is known to

be present in different copper(II) complexes with strong antiferromagnetic coupling. It

has been observed that the Cu3OH core has weaker magnetic exchange (J ≈ - 200 cm-1).

The tetrahedral sp3 hybridization forces the oxygen to be above the plane of the copper

atoms and furthermore disrupts the coplanarity of the ligand bridging network due to

HEXANUCLEAR COMPLEXES

hindered dx2-y2 overlap. The Cu3O core on the other hand has nearly coplanar geometry;

the Cu3O oxygen is only slightly raised above the plane to form a weak trimer bond. As a

result of the nearly coplanar configuration plus additional electrostatic effects, the Cu-O

bonds are shorter for the Cu3O core. Since the oxygen exhibits the more flat sp2 character,

overlap with the copper dx2-y2 orbitals still permits the oxime ligands to retain their

coplanar Cu3O geometry. This overall coplanar Cu3O structure permits larger magnetic

coupling (J ≥ - 300 cm-1), the magnetic exchange properties of triangular CuII species

result from large antiferromagnetic interaction documented by a strong exchange

coupling constant ranging up to - 1000 cm-1.

That oximate ligands generally mediate very strong antiferromagnetic exchange

interaction between two d9 copper(II) ions to provide, in some cases, a nearly complete

spin pairing at room temperature as was first authenticated in a trinuclear copper(II)

complex of pyridine-2-aldoxime. The first diamagnetic copper(II) dimer, thus historically

worth mentioning and ascribable to superexchange through the oxime bridged, was

described by Bertrand50 et al. with a centrosymmetric nearly planar six-membered ring

formed by copper atoms and two oxime (NO) groups. Strong antiferromagnetic coupling

between copper(II) ions ( J ≈ - 475 cm-1)51 was observed, revealing that the NO-group has

a remarkable ability to mediate strong antiparallel spin coupling when it acts as a

bridging ligand either through the nitrogen and oxygen atoms or only through oxygen

atom. Trinuclear copper complexes are known with planar52 or non planar53 geometrical

arrangements with the exchange coupling constants (J < - 300 cm-1 and J ≈ - 448 cm-1)

respectively, which suggest that the unusually large spin exchange interaction is not the

result of any special geometrical feature but is related to the electronic structures of the

bridging dioximato ions. Detailed inspection of the magnetostructural data54 of oximato

bridged copper(II) complexes reveal that exchange interactions (J values) show no

correlation with the distances Cu...Cu, Cu-Nox, Cu-Oox or with the nature of the basal

skeleton Cu(NO)2Cu i.e. the magnitude of exchange coupling is independent of the

degree of deviation from planarity, or deviation of the copper from the mean basal plane.

In summary it is concluded that due to the presence of oxo and oximate groups, the

exchange coupling constants are really very strong in magnitude and antiferromagnetic in

nature.

CHAPTER 6

6.6 References:

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CHAPTER 6

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Christou, Inorg. Chem., ASAP

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HEXANUCLEAR COMPLEXES

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22, 165

CHAPTER 7

CHAPTER-7

TWO RARE EXAMPLES OF NONANUCLEAR NICKEL(II)

AND COPPER(II) CLUSTERS.

Cu1

Cu2

Cu8

Cu5

Cu9

Cu6

Cu7

Cu4

Cu3

7.1 Introduction:

This chapter describes magnetostructural study of two rare examples of nonanuclear

Ni(II) and Cu(II) complexes. One over-riding feature, that helps to create self-assembled

clusters, is the presence of ligand binding sites that upon complexation form five-

membered chelate rings. This helps to prevent the ligand chelating to a single metal ion

center and forces it to look for additional Lewis acid species. There are classic examples

using ligand where special arrangements of coordination pockets allow each subunit to

interlock in a high yield self-assembly process to isolate polynuclear clusters. In essence,

in this case the self-assembly involves a polynuclear subunit and, so, highlights a possibly

useful strategy for generating even larger clusters. In recent years, self-assembly of

nanoscale high-nuclearity metal clusters via methods of coordination chemistry has

attracted increasing interest, because these supramolecules not only exhibit novel

structural characteristics as well as important applications in both biology and materials

chemistry, especially as potential precursors applied in magnetic, optical, electronic, and

catalytic processes for their size-dependent physical properties. To obtain these high-

nuclearity clusters, a common synthetic strategy has been applied to control the

hydrolysis of metal ions in the presence of appropriate chelating ligands. Many classes of

ligands are adequate to the task, including carboxylate, oxamate, oxamide, oximate and

alkoxides. Hydrophilic groups, such as oxo and hydroxo, bridge the metal ions to make

up a cluster core,

141

RARE EXAMPLES OF "NONANUCLEAR" CLUSTERS

whereas the hydrophobic groups take up positions in the periphery, preventing the core

from further aggregation and thus forming a finite-sized polynuclear complex.

It has been shown that oxime ligands can connect two transition metal

ions due to their versatility in coordination modes. Also the ability of the oxime group to

efficiently transmit magnetic coupling has been well doccumented.14 There are only ten

structurally characterized oximate bridged nickel(II) complexes reported in last 30 years,

only seven of which have been subjected to magnetic susceptibility measurements. Thus

no correlation between structural and magnetic properties for such complexes has yet

been obtained and hence more oximate bridged paramagnetic complexes of nickel(II) are

warranted. Since nickel(II) is known to have a large single-ion zero-field splitting and the

geometrical parameters, which in Ni complexes are well understood, gives rise to

ferromagnetic coupling, we wish to study the structure and magnetic properties of a

nonanickel(II) cluster. The complexation of nickel(II) by pyridine-2-aldoxime in aqueous

solution was studied by Orama et.al1 and the structure of the nickel(II) complex of

pyridine-2-aldoxime, a neutral tris complex was found in the solid state to consist of the

monomeric [Ni(PyAH)(PyA)2] units held together by two OH...O hydrogen bonds

between the oxygen atoms. This is an apparent contrast to the analogous complexes of

copper(II), both of which in aqueous solution and in solid state are characterized by the

presence of trinuclear complex species [Cu3(PyA)3(OH)]2+ containing a Cu3OH central

core.2 We herein present a new nonameric nickel(II) complex with syn-2-pyridine

aldoxime ligand, [Ni9(PyA)10(µ3-OH)2(µ2-OH)2(µ2-OH2)2(H2O)6](ClO4)4•12H2O

underlining the versatility of this ligand to adopt a variety of coordination modes.

Moreover there are very few nonanickel(II) complexes3 known, one of which has been

subjected to magnetically characterized.4 The difficulties in analyzing large clusters

magnetochemically prompted us to characterize the nonanuclear Ni(II) cluster

magnetostructurally and compare the nature of exchange interaction through oximate and

hydroxo bridging ligands reported earlier.

The magnetism of bis-(µ-hydroxo)- or (µ-alkoxo) dicopper(II)

complexes has been the subject of extensive investigations for the last two decades.5a

According to Hatfield and Hodgson, antiferromagnetic interactions between copper(II)

ions become larger with increasing Cu-O-Cu angle in these complexes.5 This was

reasonably explained in terms of quantum-mechanical treatments by Hoffmann et al.6a

and Kahn.6b However this rationale had been confined to doubly bridged systems with the

Cu-O-Cu angle in the range 95-105° until Mckee et al.7 and Kida et al.8 reported the

142

CHAPTER 7

synthesis and magnetism of copper(II) complexes with a single alkoxide bridge derived

from 1,3-diamino-2-propanol. Since the Cu-O-Cu angle in such complexes is much larger

(120-135°) than that of the other bridging ligands, substantially stronger

antiferromagnetic interactions are expected in spite of the fact that the superexchange

pathways due to the presence of other ligands might be expected to be different in

magnitude and sign. It was also revealed that when another bridging group is added to the

system, the antiferromagnetic interaction is substantially weakened or enhanced,

depending on the second ligand. This fact was reasonably interpreted in terms of

Hoffmann's theory that the matching of symmetries of the HOMOs of the bridging

groups determines whether the two bridges work complementarily or

countercomplementarily in the superexchange interaction. This theory is essentially

important when the magnetism of a polynuclear complex possessing two different

bridging groups is considered. This fact has been recognized in some other examples.9

Moreover there are very few nonacopper(II) complexes12 known. Thus a nonanuclear

copper(II) complex was isolated and characterized magnetically where the spin exchange

interaction was mediated through alkoxo, hydroxo and alkoxo-hydroxo bridge. Magnetic

properties of this cluster follows the same trend reported earlier.10,12

CCH3

CH3

COH

NOH

(a) (PyAH) (b) L'H3

Figure 7.1: (a) Ligand (PyAH) for the nonanuclear Ni(II) complex; (b) Ligand (L'H3) for the

nonanuclear CuII complex.

7.2 Synthesis:

Nonanuclear nickel(II) and copper(II) complexes respectively are isolated by

self assembly, using tridentate oxime (PyAH) and pentadentate schiff base ligand(L'H3).

The schematic diagram of the synthesis is given below:

143

RARE EXAMPLES OF "NONANUCLEAR" CLUSTERS

PyAH + NiCl2. 6H2O + NaOH + NaClO4

H2O

(a)

[Ni9(PyA)10(µ3-OH)2(

2-OH)2(

2-OH2)2(H2O)6](ClO4)4. 12H2O

LH3 + Cu(ClO4)2. 6H2O + Et3N

(b) MeOH

[Cu9(L)4(µ3-OH)4(MeOH)2](ClO4)2. 6MeOH

7.3 Infrared and Mass Spectroscopy:

The relevant bands in IR spectra of comparable pyridine-2-aldoximato

containing heteronuclear CrIIIMII and FeIIIMII complexes have been reported earlier by Ross

et al16 and the spectra of 16 are also very similar. A notable feature for 16 are the sharp NO

stretching bands at 1141, 1120, 1031 cm-1. The presence of two different coordination

modes of the oxime group in 16 is consistent with the splitting. A broad O-H stretching band

around 3441 cm-1 indicates the presence of the OH groups in the compound while the

stretching band for ClO4 was also identified in the region of 1089 and 626 cm-1. The IR

spectrum of compound 17 revealed that the broad stretching band around 3463 cm-1

indicates the presence of the OH groups in the compound while the stretching bands for

ClO4 were also identified in the region of 1089 and 626 cm-1.

Electrospray-ionaziation mass spectrometry (ESI-MS) in the positive ion mode

does not provide signal for unambiguous characterization and shows only the

monopositively charged species [(PyA)5Ni3]+ as the base peak with the peak of

[(PyA)6Ni4(ClO4)]+ (10%). On the other hand the signal for [L2Cu4(OH)]+ of 17 is the base

peak, together with the peak for the fragment [L3Cu6(OH)]+ (50%) and [L4Cu8(OH)4] (15%).

144

CHAPTER 7

7.4 X-ray Structure:

7.4.1 Solid State molecular structure of [Ni9(PyA)10(µ3-OH)2(µ2-OH)2(µ2-

OH2)2(H2O)6] (ClO4)4. 12H2O

The asymmetric unit contains of a discrete nonanuclear tetracation, four perchlorate

anions and twelve water molecules of crystallization. There are two types of oximic

groups, (i) a two atom -N-O bridging group O1, O11, O31, O41, O51, O81 and (ii) µ2-O

bridging oximate O21, O61, O71, and O91. The nonanuclear complex can be described

as consisting of two [NiII4(PyA)5(µ3-OH)(µ2-OH)(µ-OH2)(H2O)3]+moieties are connected

to a centrally placed Ni(II) ion, Ni(7) through two µ3-OH groups O(153), O(156) and four

µ2-Oox, O(21), O(61), O(71) and O(91) of the ligands and yielding an Ni(7)O6 core. As

shown in Figure 7.2, all the nickel centers are 6-fold coordinate and the structure contains

an octahedral NiO6 central core and four different NiN4O2 and NiN2O4 environments. All

of the oxime groups are deprotonated, and the nine nickel atoms are linked together via

several bi-or trifurcated oximato, hydroxo and water bridges. Two nickel atoms (Ni1 and

Ni3) display pseudo-octahedral geometry with NiN4O2 coordination spheres with two

pyridine nitrogen atoms, two imine nitrogen atoms and one µ2-OH and the 6th

coordination mode is satisfied through µ-bridging water molecules O(151) and O(154).

As shown in Table 7.1, the Ni-µ2-O(151) and Ni-µ2-O(154) bond lengths [2.129(6)-

2.147(7) Å] are significantly longer than the bond distances of Ni-µ-O(152), Ni-µ-

O(153), Ni-µ-O(155) and Ni-µ-O(156) [2.000(6)-2.032(6) Å] and thus O(151), O(154)

are assigned as µ2-bridging water molecules. The coordination mode around Ni(2)and

Ni(9) are N2O4, one pyridine nitrogen, one imine nitrogen, one µ3-OH, two oximate

oxygen, and the 6th coordination is satisfied by µ-bridging water molecules. The

coordination environment around Ni(4) and Ni(6) differs from that of Ni(2) and Ni(9) in

that their is only one µ- bridging oxygen of the oximate instead two, µ2-OH instead of µ3-

OH and terminally coordinated water. Whereas Ni(5) and Ni(8) are also in an N2O4

octahedral environment with one pyridine nitrogen, one imine nitrogen, one µ- bridging

oxygen from the oximates, one µ3-OH and two coordinated water molecules. The

distortion from octahedral geometry for the nickel centers are more pronounced; the trans

donor angles deviate from 180° by nearly 12°. Selected bond lengths and angles are given

in Table 7.1.

The C=N and N-O distances of the oximate moieties are in the ranges of

1.28 and 1.36 Å respectively and nearly identical to the corresponding distances for other

145

RARE EXAMPLES OF "NONANUCLEAR" CLUSTERS

comparable structures.16d-e,17 The Ni-O distances lie in the range of 2.005 Å to 2.174 Å as

expected, the Ni-µ2-Oox bond lengths are significantly longer than the Ni-Oox bond

distances. The Ni-N bond distances are consistent with normal covalent bonds for high-

spin d8 Ni(II) ions with oximate ligands. The Ni-Nox bond lengths are shorter than the Ni-

Npy bond lengths as is evidenced from the X-ray structure. The µ3-OH(153) group acts as

a bridge between Ni(2), Ni(7) and Ni(8) atoms, similarly µ3-OH(156) group acts as a

bridge between Ni(5), Ni(7) nd Ni(9). The µ2-OH(152) and OH(155) groups are bridging

ligands between Ni1 and Ni6; Ni3 and Ni4 respectively. In the cluster there are two

different sets of Ni-O-Ni bond angles lying in the ranges 93.7-102.2 and 108.4-114.6°

Figure 7.2: ORTEP and labeling scheme for NiII9 (17)

There are eight strong hydrogen bondings prevailing between the oximate, hydroxo and

water oxygen atoms and is shown as dotted lines in the Figure 7.3. The OH...O bond

distances lie in the ranges of 2.625-2.757 Å and are listed in Table 7.1A. These

chemically significant hydrogen bondings are responsible for the stabilization of the

supramolecular metallocyclic core in cluster 16.

146

CHAPTER 7

Figure 7.3: Schematic view of the hydrogen bonding in the Ni9 core structure.

Table 7.1: Selected Bond Lengths (Å) and Angles (deg) [NiII9(PyA)10(µ3-OH)2(µ2-OH)2(H2O)6](ClO4)4

.12H2O (16)

Ni(1)•••Ni(2) 3.479 Ni(2)•••Ni(8) 3.351

Ni(3)•••Ni(4) 3.379 Ni(4)•••Ni(5) 3.396

Ni(5)•••Ni(9) 3.367 Ni(5)•••Ni(7) 3.117

Ni(3)•••Ni(9) 3.486 Ni(7)•••Ni(8) 3.125

Ni(7)•••Ni(9) 3.378 Ni(1)•••Ni(6) 3.486

Ni(1)-N(2) 2.019(7) Ni(4)-N(62) 2.052(8)

Ni(1)-N(12) 2.044(7) Ni(4)-N(69) 2.070(8)

Ni(1)-N(19) 2.056(8) Ni(4)-O(21) 2.171(6)

Ni(1)-N(9) 2.056(7) Ni(4)-O(41) 2.040(7)

Ni(1)-O(151) 2.147(7) Ni(4)-O(42) 2.096(6)

Ni(1)-O(152) 2.008(6) Ni(4)-O(155) 2.004(6)

147

RARE EXAMPLES OF "NONANUCLEAR" CLUSTERS

Ni(2)-N(22) 2.068(7) Ni(5)-N(82) 2.031(8)

Ni(2)-N(29) 2.083(8) Ni(5)-N(89) 2.049(9)

Ni(2)-O(11) 2.071(6) Ni(5)-O(52) 2.102(7)

Ni(2)-O(31) 2.043(6) Ni(5)-O(53) 2.090(7)

Ni(2)-O(151) 2.142(6) Ni(5)-O(91) 2.118(6)

Ni(2)-O(153) 2.032(6) Ni(5)-O(156) 2.002(6)

Ni(3)-N(42) 2.038(7) Ni(6)-N(92) 2.058(8)

Ni(3)-N(49) 2.070(8) Ni(6)-N(99) 2.082(8)

Ni(3)-N(52) 2.036(7) Ni(6)-O(1) 2.052(6)

Ni(3)-N(59) 2.075(7) Ni(6)-O(62) 2.117(6)

Ni(3)-O(154) 2.129(6) Ni(6)-O(71) 2.174(6)

Ni(3)-O(155) 2.005(6) Ni(6)-O(152) 2.008(6)

Ni(7)-O(21) 2.110(6) Ni(8)-N(32) 2.034(8)

Ni(7)-O(61) 2.160(6) Ni(8)-N(39) 2.074(7)

Ni(7)-O(71) 2.132(6) Ni(8)-O(61) 2.122(6)

Ni(7)-O(91) 2.137(6) Ni(8)-O(82) 2.065(7)

Ni(7)-O(153) 2.001(6) Ni(8)-O(83) 2.108(6)

Ni(7)-O(156) 2.004(6) Ni(8)-O(153) 2.000(6)

Ni(9)-N(72) 2.055(7) Ni(7)-O(21)-Ni(4) 112.7(3)

Ni(9)-N(79) 2.091(8) Ni(8)-O(61)-Ni(7) 93.7(2)

Ni(9)-O(51) 2.068(6) Ni(7)-O(71)-Ni(6) 112.4(3)

Ni(9)-O(81) 2.055(6) Ni(7)-O(91)-Ni(5) 94.2(2)

Ni(9)-O(154) 2.131(6) Ni(2)-O(151)-Ni(1) 108.4(3)

Ni(9)-O(156) 2.040(6) Ni(1)-O(152)-Ni(6) 114.6(3)

Ni(7)-O(153)-Ni(8) 102.7(3)

Ni(8)-O(153)-Ni(2) 112.4(3)

Ni(7)-O(153)-Ni(2) 113.9(3)

Ni(3)-O(154)-Ni(9) 109.8(3)

Ni(3)-O(155)-Ni(4) 114.5(3)

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Ni(7)-O(156)-Ni(5) 102.2(3)

Ni(5)-O(156)-Ni(9) 112.8(3)

Ni(7)-O(156)-Ni(9) 113.3(3)

Table 7.1A: Selected Bond Lengths (Å) for the hydrogen bonding in the NiII

9 cluster.

O(152)•••HO(153) 2.652 O(21)•••HO(154) 2.643

O(81)•••HO(62) 2.707 O(155)•••HO(154) 2.632

O(31)•••HO(42) 2.757 O(71)•••HO(151) 2.625

O(61)•••HO(53) 2.704 O(91)•••HO(82) 2.716

7.4.2 Solid State molecular structure of [Cu9(L')4(µ3-OH)4(MeOH)2](ClO4)2 • 6

MeOH (17)

The asymmetric unit consists of one half of the nonanuclear dication which resides on a

crystallographic inversion center, one perchlorate anion and three methanol molecules of

crystallization. The X-ray structure clearly illustrates the formation of the nonanuclear

cluster. An ORTEP view of the dication is shown in the Figure 7.4. Selected bond lengths

and angles are listed in Table 7.2 The nonanuclear complex consists of four alkoxo

bridged dinuclear units {Cu2L}+, that are covalently linked by µ3-OH bridging ligands to

form the nonacopper(II) metallocyclic core. The nonacopper cluster can be described as

consisting of two [CuII4L2(µ3-OH)2(MeOH)] moieties connected to a centrally placed

Cu(II) ion, Cu(5) through four µ3-OH groups and two µ3-alkoxo bridges of the ligands

and yielding a Cu(5)O6 core. Thus the centrosymmetric aggregate can be regarded as two

irregular tetrahedral [CuII4L2(µ3-OH)2(MeOH)]2+ units linked via a central CuII ion,

Cu(5), at its inversion center. As shown in the Figure 7.4, the structure contains an

octahedral CuO6 central core and all other copper(II) ions are in distorted CuNO4

environments. All the ligands are deprotonated and the nine copper atoms are linked

together via several bi-or trifurcated endogenous-alkoxo, exogenous-hydroxo groups and

enolized oxygen atoms. In the {Cu2L}+ unit, the trianionic ligand displays N2O3-

pentadentate coordination mode with alkoxide oxygen acting as the endogenous bridging

ligand.

149

RARE EXAMPLES OF "NONANUCLEAR" CLUSTERS

Figure 7.4: ORTEP and labeling scheme for CuII

(18)

All the five coordinated copper ions, Cu(1), Cu(2), Cu(3), Cu(4) and its symmetric

equivalent centers are in distorted NO4 square pyramidal geometry with an unpaired

electron in the dx2-y2 orbital. The basal planes around the copper centers are formed from

the imine nitrogen, alkoxo oxygen, the enolized oxygen atom of the ligand moiety and

the hydroxo oxygen atoms. The crystal structure gives τ values in the range 0.08-0.26

indicating an essentially square-pyramidal (4 + 1) coordination geometry of the metal in

17.18 In a five coordinate system, ideally square pyramidal geometry is associated with α

= β = 180° for A is the axial ligand (where α and β are the basal angles). In the great

majority of real square pyramidal systems, metal is displaced out of the equatorial plane

toward the axial ligand. The geometric parameter τ is defined as [(β - α)/60] which is

applicable to five coordinate environment as an index of degree of trigonality, within the

structural continuum between trigonal bipyramidal and square pyramidal geometries. For

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CHAPTER 7

a perfectly square pyramidal geometry τ is zero, while it becomes unity for a perfect

trigonal bipyramidal geometry. The Cu-N bond distances in all the eight copper ions,

Cu(1), Cu(2), Cu(3), Cu(4) and its symmetric equivalent centers are 1.91 Å. A close look

into the X-ray structure illustrates the presence of two different types of enolized oxygen

atoms in the complex 17; O(37) and O(47) are bifurcated, whereas O(7) and O(17) are

monodentate. The O(12) and O(42) alkoxo groups are acting as a µ3-bridge between

{Cu(1), Cu(2) and Cu(4)} and {Cu(3), Cu(4) and Cu(5)} respectively. The Cu (1)-O(12)

and Cu(2)-O(12) bond distance is 1.95 Å(basal plane), whereas the Cu(4)-O(12) bond

distance of 2.5 Å is longer compared to the previous bond distance. Similarly the Cu(5)-

O(42) bond distance of 2.4 Å is significantly larger compared to Cu(3)-O(42) and Cu(4)-

O(42) bond distances of 1.94 Å. On the other hand O(37) and O(47) act as bridges

between {Cu(1), Cu(3)} and {Cu(2),Cu(4)} respectively.

Cu5

Cu3

Cu4

Cu3

Cu1

Cu2

Cu1

Figure 7.5A: Core structure of the nonacopper(II) cluster 17

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RARE EXAMPLES OF "NONANUCLEAR" CLUSTERS

The central copper ion Cu(5) has been subjected to Jahn-Teller distortion, as is evident

from the two significantly larger Cu(5)-O(42) and Cu(5)-O(42A) bond distances of 2.4 Å

compared to Cu(5)-O(1), Cu(5)-O(1A), Cu(5)-O(2), Cu(5)-O(2A) bond distances of ∼

1.97 Å . The bond distances of copper with oxygen atoms are also dissimilar (Cu-Oav =

1.9 and 2.6 Å) in case of µ2-alkoxo groups [O(37) and O(47)]. The µ3-hydroxo groups

O(1) and O(2) connect {Cu(1), Cu(3), Cu(5)} and {Cu(2), Cu(4), Cu(5)} respectively.

The average Cu-OH(µ3-) bond distance is 1.975 Å. The nonseparated Cu...Cu distances

lie in the range from 2.88 Å to 7.3 Å in the nonanuclear cluster. The entire Cu...Cu

separations are given in the table 6.2. A notable outcome of this cluster is the presence of

different Cu-O-Cu bond angles which lie in the range 83.95 to 132°. It is to be mentioned

that the Cu-O(H)-Cu angles are in the range 91.81 to 133.92°, whereas the Cu-µ3-O(R)-

Cu and Cu-µ2-O(R)-Cu angles fall in the range 79.56 to 130.26°, and 77.65° respectively.

The dihedral angles (ϕ) between the basal planes are 72.8° within the {Cu2L}+

moiety. This suggests a significant deviation from the planarity of the two planes. The

dihedral angles between the two interunit basal planes {Cu(1) and Cu(3)} and {Cu(2) and

Cu(4)} having hydroxide bridging ligands are 107.8 and 113.2° respectively. Strong

deviation from planarity may reduce the magnitudes of the exchange coupling

considerably.

The crystal structure of 17 exhibits chemically significant hydrogen-bonding

interaction between the complex and the lattice molecules, and also between oxygen

atoms of the ligand and the coordinated methanol molecules. So the hydrogen bonding

network may stabilize the core conformation. The O(2)...O(100), O(1)...O(100),

O(7)...O(60), O(74)...O(80) distances of 2.73, 2.85, 2.84, and 2.83 Å respectively with O-

H....O angle of ∼ 160, 155, 160 and 168° respectively indicate the presence of strong

hydrogen-bonding interactions.

The crystal structure of 17 is of importance as structurally characterized discrete

molecular nonanuclear copper(II) complexes are limited in number.11 Again the diversity

of the core structures in these high-nuclearity copper(II) complexes means any

meaningful comparison difficult.

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CHAPTER 7

Table 7.2: Selected Bond Lengths (Å) and Angles (deg) [CuII9(L)4(µ3-OH)4(MeOH)2](ClO4)2 .6 MeOH

(17)

Cu(1)•••Cu(2) 3.2 Cu(1)•••Cu(5) 3.64

Cu(1)•••Cu(3) 3.25 Cu(2)•••Cu(3) 3.33

Cu(3)•••Cu(4) 3.4 Cu(3)•••Cu(5) 2.92

Cu(2)•••Cu(5) 3.64 Cu(2)•••Cu(4) 2.88

Cu(4)•••Cu(5) 3.03 Cu(4)•••Cu(4A) 6.06

Cu(2)•••Cu(2A) 7.25 Cu(3)•••Cu(3A) 6.94

Cu(1)-N(10) 1.920(2) Cu(3)-N(40) 1.913(2)

Cu(1)-O(7) 1.914(1) Cu(3)-O(37) 1.901(1)

Cu(1)-O(12) 1.947(1) Cu(3)-O(42) 1.944(1)

Cu(1)-O(1) 1.980(1) Cu(3)-O(1) 1.999(1)

Cu(1)-O(37) 2.579(6) Cu(3)-O(60) 2.444(6)

Cu(2)-N(14) 1.911(2) Cu(4)-N(44) 1.912(2)

Cu(2)-O(17) 1.877(1) Cu(4)-O(47) 1.888(1)

Cu(2)-O(12) 1.949(1) Cu(4)-O(42) 1.945(1)

Cu(2)-O(2) 1.993(1) Cu(4)-O(2) 2.013(1)

Cu(2)-O(47) 2.612(1) Cu(4)-O(12) 2.499(6)

Cu(5)-O(1) 1.971(1) N(10)-Cu(1)-O(1) 158.82(8)

Cu(5)-O(1A) 1.971(1) O(12)-Cu(1)-O(7) 174.75(7)

Cu(5)-O(2) 1.960(1) N(14)-Cu(2)-O(2) 166.89(8)

Cu(5)-O(2A) 1.960(1) O(17)-Cu(1)-O(12) 175.97(7)

Cu(5)-O(42) 2.395(1) N(40)-Cu(3)-O(1) 161.64(8)

Cu(5)-O(42A) 2.395(1) O(37)-Cu(3)-O(42) 172.56(7)

N(44)-Cu(4)-O(2) 176.85(8)

O(42)-Cu(4)-O(47) 172.15(7)

Cu(1)-O(12)-Cu(2) 111.43(8) Cu(2)-O(47)-Cu(4) 77.65

Cu(1)-O(1)-Cu(5) 133.92(9) Cu(2)-O(12)-Cu(4) 79.56

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RARE EXAMPLES OF "NONANUCLEAR" CLUSTERS

Cu(1)-O(1)-Cu(3) 109.59(8) Cu(3)-O(1)-Cu(5) 94.73(7)

Cu(1)-O(12)-Cu(4) 130.26 Cu(3)-O(42)-Cu(4) 123.18(9)

Cu(1)-O(37)-Cu(3) 91.79 Cu(3)-O(42)-Cu(5) 83.95(6)

Cu(2)-O(2)-Cu(5) 132.92(9) Cu(4)-O(42)-Cu(5) 88.00(6)

Cu(2)-O(2)-Cu(4) 91.81(7) Cu(4)-O(2)-Cu(5) 99.49

7.5 Magntic Properties:

The magnetic susceptibility data for polycrystalline samples of 16 and 17 were

collected in the temperature range 2-290 K in an applied magnetic field of 1T and are

displayed in Figures 7.6 and 7.9 respectively as plots of the effective magnetic moment

(µeff) versus temperature (T).

The plot of µeff vs. T for NiII9 shows typical antiferromagnetic behavior, and the

magnetic moment µeff /molecule of 17 is 8.2 µB (χMT = 8.4 emu mol-1) at 290 K, smaller

than the expected value for nine isolated Ni(II) ions S = 1 (9 x 1.00 = 9.00 emu mol-1)

assuming g = 2.00 (which is unrealistic for a Ni(II) ion, which always has g values >

2.00) decreases monotonically with decreasing temperature until it reaches a value of

2.51µB (χMT = 0.8 emu mol-1) at 1.96 K. This temperature dependence is in agreement

with antiferromagnetic behavior. Complex 17 contains 9 Ni(II) centers, with total spin

from 0 to 9, owing to the size and low symmetry of the molecule, it is not possible to

apply Kambe method.19

To fit and interpret the magnetic susceptibility data of complex 16, first it is

necessary to find all the possible magnetic pathways in the complicated but regular

structure of the complex 16. Close examination of the structure gives the pathways shown

in scheme 7.5. From this scheme two different superexchange pathways can be identified,

due to the different bridging modes, whereas the g value is considered to be isotropic and

equal for all Ni(II) ions. A schematic core for the nonanickel(II) cluster is shown below.

154

CHAPTER 7

N22

O21

O41

N42

O155

O154

N52

O51

Ni4

Ni3

Ni9

Ni5

O152

O11

N12

O31N32

Ni1

N92

O153

O91

Ni6

N62

O61

N82

O81

N72

O71

Ni8

Ni2

Ni7

O156

Perspective view of the coordination environment around each nickel centers in NiII

9 cluster

The exchange coupling model shown in Figure 7.5 was considered for simulation of the

experimental magnetic data using irreducible tensor operator (ITO)17 mathematical

approach with the Heisenberg Hamiltonian in the form H = -2JSiSj. The experimental

magnetic data have been fitted using the Hamiltonian, H = -2J1(S1S2 + S1S6 + S3S4 +

S3S9) -2J2(S2S7 + S6S7 + S8S7 + S4S7 + S5S7 + S9S7 +S2S8 + S5S9) ; where the numbering

of the spins follows the numbering of the nickel atoms in Figure 7.5.

155

RARE EXAMPLES OF "NONANUCLEAR" CLUSTERS

Ni1Ni7

Ni4

Ni2

Ni6

Ni3

Ni5

Ni8

Ni9

J1J1

Figure 7.5: Coupling Scheme

50 100 150 200 250 300

µeff / µB

T/K

[NiII

9(PyA)10(µ3-OH)2(µ2-OH)2(µ-OH2)2(H2O)6](ClO4)4

Figure 7.6: Plot of effective magnetic moment as a function of temperature. The solid line represents

the best least-squares fit parameters given in the text.

Such a complicated magnetic structure represents an interesting challenge in order to fit

and interpret the susceptibility data, J1 and J2 pathways seem to be most defined, where

the J1 pathway represents the exchange interaction between the nickel centers through (-

N-O) and µ2-hydroxo, whereas J2 pathway represents the exchange interaction between

the nickel centers through µ2-oxygen atoms of the oximate ligands and µ3-hydroxo

ligands. In adopting this procedure we have reduced the overparametarization. The total

156

CHAPTER 7

degeneracy of spin levels for nonanuclear nickel (II) with single ion SNi = 1 is 39, a

number which grows very fast beyond the possibilities of handling with any computer. So

it is really not a trivial task to diagonalize this 19683 X 19683 matrix. Thus it is apparent

that procedures are required which employ symmetry in order to reduce the dimension of

the matrices. Here in the approximation we have reduced the matrix by taking 5 nickel

centers, as it was described earlier that two tetranuclear units are connected with the

central nickel(II) ion. In doing so the total degeneracy is now 35 and now the matrix

dimension is reduced to 243X243. The best fit parameters obtained where J1 = - 26.54

cm-1 and J2 = -7.02 cm-1 with g = 2.15. The bridging geometries between the nickel

centers exhibit small variations, and this leads to variation in the exchange coupling

constant.

It is known that the exchange interaction is ferromagnetic when the Ni-O-Ni angle

falls below 98°, above which the exchange interaction is antiferromagnetic. Since in our

case just two Ni-O-Ni angles are less than 98°, and all other Ni-O-Ni angles are greater

than 98° and lie in the ranges 108-114°, the exchange interaction leads complex 16 is an

antiferromagnetically coupled cluster. This can be explained in terms of interaction of the

magnetic orbitals of Ni(II) with SNi = 1 which are singly occupied (dx2 -y2)1 and (dz2)1

orbitals and the dominant interactions prevailing are listed below,

dx2-y2⎪⎪ σsp2(NO) ⎪⎪ d'x2-y2 antiferromagnetic

dz2 ⎪⎪σsp2(NO) ⎪⎪ d'z2 antiferromagnetic

dx2-y2 ⎪⎪σsp2(NO) ⎪⎪ d'z2 ferromagnetic.

All reported oximate bridged nickel(II) complexes14-15 accordingly exhibit moderate to

weak antiferromagnetic interactions, ranging from -7 cm-1 to - 40 cm-1.

The antiferromagnetically coupled nonanuclear nickel(II) complex possesses ST =

1 ground state, as is also evidenced from the variable temperature variable field (VTVH)

magnetic measurement. From the best simulation we have evaluated the ZFS (D)

parameter of the ST = 1 ground state to be DS=1 = 2.7 cm-1

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RARE EXAMPLES OF "NONANUCLEAR" CLUSTERS

0.5 1.0 1.5 2.0 2.5

0.23

0.46

0.69

0.92

M / Ngß

ßH / kT

7 T

4 T

1 T

Figure 7.7: Plot of variable temperature variable field magnetic measurements (VTVH). The solid line

represents the best least-squares fit parameters given in the text.

In conclusion we have been able to isolate the NiII9 complex by using a tridentate oxime

ligand. The metal ions are in a distorted octahedral coordination sphere. The complex

exhibits moderate antiferromagnetic exchange interaction.

The magnetic moment µeff/molecule for 17, CuII9, of 4.59 µB (χM•T = 2.63

cm3•K•mol-1) at 290 K, is smaller than the typical value for nine isolated Cu(II) ions S =

0.5 (9 x 0.375 = 3.375 cm3•K•mol-1) assuming g = 2.00 (which is unrealistic for a Cu(II)

ion, which typically has g values > 2.00) decreases monotonically with decreasing

temperature until it reaches a value of 3.34 µB (χM•T = 1.39 cm3•K•mol-1) at 70 K and

then starts to increase slowly and reaches a value of 3.38 µB (χM•T = 1.43 cm3•K•mol-1)

at 20 K and then finally decreases to a value of 2.7 µB (χM•T = 0.91 cm3•K•mol-1). This

temperature dependence behavior agrees well with that expected for an antiferromagnetic

exchange coupling between the copper(II) ions, leading to an irregular spin state

structure. So in the µeff vs. T plot, the minima at 70-20 K indicating the presence of

irregular spin levels in the compound.

Complex 17 contains 9 Cu(II) centers, with total spin from 0 to 4.5, owing to

the size and low symmetry and also due to the complexity of the molecule, here also it is

not possible to apply the Kambe method19 of vector coupling to model the exchange

coupling scheme. To fit and interpret the magnetic susceptibility data of complex 17,

firstly it is necessary to find all possible magnetic pathways in the complicated but

regular structure of the complex 17. Close examination of the structure gives the

158

CHAPTER 7

pathways shown in scheme 7.8. From this scheme four different superexchange pathway

can be identified, due to the different bridging modes, whereas the g value is considered

isotropic and equal for all Cu(II) ions.

Cu1

Cu2

Cu8

Cu5

Cu9

Cu6

Cu7

Cu4

Cu3

Figure 7.8: Coupling Scheme

The exchange coupling model shown in Figure 7.8 was considered for

simulation of the experimental magnetic data using the irreducible tensor operator (ITO)

mathematical approach with the Heisenberg Hamiltonian in the form H = -2JSiSj. The

experimental magnetic data have been fitted using the Hamiltonian, H = -2J1(S1S2 + S9S8

+ S3S4 + S6S7) - 2J2(S2S4 + S7S8) - 2J3( S1S6 + S3S9) - 2J4(S1S5 + S2S5 + S3S5 + S4S5 +

S6S5 + S7S5 + S8S5 + S9S5); where the numbering of the spins follows the numbering of

the copper(II) atoms in Figure 7.8.

50 100 150 200 250 300

2.5

3.0

3.5

4.0

4.5

5.0

µeff / µB

T/K

Figure 7.9: Magnetic data for CuII

(18) plot of µeff vs. T. The bold squares represent the experimental

data while the solid line represents the simulation.

159

RARE EXAMPLES OF "NONANUCLEAR" CLUSTERS

Such a complicated magnetic structure represents an interesting challenge in order to fit

and interpret the susceptibility data. It is logical to consider J1, J2, J

3 and J4 pathways

where the J1 pathway represents the interaction between the copper centers through

alkoxo bridge in the binuclear {Cu2L}+ unit; whereas J2 and J3 pathway represent the

interaction between the copper centers through (alkoxo, enolized µ2-O and hydroxo) and

enolized µ2-O-hydroxo) groups respectively; on the other hand J4 defines exchange

interaction between the copper(II) ions through hydroxo bridge. The total degeneracy of

spin levels for nonanuclear copper (II) with single ion SCu = 0.5 is 29, giving rise to a

matrix of 512 X 512. From the best fit, the parameters obtained are gCu = 2.30, J1 = -

193.3 cm-1; J2 = - 27.4 cm-1; J3 = - 6.4 cm-1; J4 = - 53.1 cm-1, with a R agreement factor

(R = (χMcalc – χMexp)2/(χMexp)2) of 2.9 × 10–4.

But to reduce the possible over parameterization another set of spin modeling was taken

into consideration with the Heisenberg Hamiltonian; H = -2J1(S1S2 + S9S8 + S3S4 +

S6S7) - 2J2(S2S4 + S7S8 + S1S6 + S3S9) - 2J3(S1S5 + S2S5 + S3S5 + S4S5 + S6S5 + S7S5 +

S8S5 + S9S5), where J1, J2, and J3 define the exchange interactions between the

copper(II) ions through alkoxo, (alkoxo-hydroxo-enolized µ2-O) and hydroxo bridges

respectively. In the previous scheme two different exchange coupling constants through

alkoxo-hydroxo-enolized µ2-O and enolized µ2-O-hydroxo bridges exchange

interactions were considered. By using a "three-J" model overparametarization is

reduced.

Cu1

Cu2

Cu8

Cu5

Cu9

Cu6

Cu7

Cu4

Cu3

Figure 7.10: Coupling Scheme.

160

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As an approach to the J coupling constants, a fit based on the interaction was performed

by means of the CLUMAG program, which uses the irreducible tensor operator

formalism (ITO) on the Hamiltonian. Best fit parameters are in good accordance with the

expected values for the three kinds of bridges, J1 = - 189.1 cm-1, J2 = - 22.7 cm-1, J3 = -

45.7 cm-1, g = 2.29 with a R agreement factor (R = (χMcalc – χMexp)2/(χMexp)2) of 1.37 ×

10–4. In this case, attempts to fit the system with a "three-J" scheme give good

mathematical fits and realistic coupling constants values.

Magnetostructural correlations have been found to be very successful in the

description of the Cu...Cu coupling in binuclear complexes with double bridging

ligands. It has been shown that if the Cu-O-Cu angle exceeds 97.5°, an

antiferromagnetic interaction is observed, if less a ferromagnetic interaction.23

Significant decrease of the values of exchange coupling constants was observed due to

the displacement of the Cu2O fragment from planarity due to displacement of metal ions

from the ligand plane.24 To avoid over parameterization in the calculation for the

compound 17, only the interactions deemed most likely to dominate the coupling were

considered. It is clear from the vast amount of research that the nature and the strength

of the exchange are chiefly affected by the Cu-O-Cu angle. In general, the coupling is

antiferromagnetic and J decreases as Cu-O-Cu angle becomes more acute. For each type

of bridge there is predicted critical value of Cu-O-Cu angle where J changes sign to

become ferromagnetic. The antiferromagnetic interaction is favoured by the nature of

the bridge in the order OPh > OR > OH. Other electronic and geometric factors have

also been found to exert a particular influence on the value of J, such as the coordination

geometry around Cu(II),20 the Cu-O bond distances,21 or the electronegativity of the

additional ligands bound to the metals.22 Because of the approximations included in this

analysis, however, the numbers obtained must be regarded for scepticism. The structural

differences of this cluster 17 prevent a systematic comparison between their J values.

However, the strongest interaction, which controls the coupling, can be compared.

As expected, the magnetic response of compounds 17 is dominated by the strong

antiferromagnetic coupling through the alkoxo bridge in the {Cu2L}+ which shows large

Cu–O–Cu bond angles. A strong antiferromagnetic exchange is expected when the Cu-O-

Cu bridging angle is close to 180°, whereas for angles close to 90°, the interaction is

expected to be either ferromagnetic or weakly antiferromagnetic. Therefore, in spite of

the relatively similar coupling constants, the exchange coupling through different Cu-O-

Cu bond angle based on alkoxo, hydroxo and alkoxo-hydroxo bridge has non-trivial

161

RARE EXAMPLES OF "NONANUCLEAR" CLUSTERS

features that should be analyzed separately. In spite of a different coordination

polyhedron, the interaction through alkoxo bridge coupling reaches a J value comparable

to that obtained for the interaction between the two copper planes with dx2-y2 interaction.

Owing to the square pyramidal geometry of Cu(1) and Cu(2), the metallic components of

their magnetic orbitals is dx2-y2 which points towards the equatorial ligands. As a

consequence strong overlap is expected with the alkoxo-bridge. From the structural data,

the coupling constant associated with the alkoxo bridge (J1) should be high in view of the

large Cu–O–Cu bond angle and weaker value should be expected for the interaction

through the enolized µ2-O-hydroxo bridge (J2) due to countercomplementary interactions

promoted by the exogenous hydroxo bridge and expected to be weaker compared to the

interaction mediated through alkoxo bridge only and are in good agreement with entities

reported elsewhere. So it can be anticipated that the observed weaker antiferromagnetic

coupling(J2) compared to that of alkoxo bridge exchange interaction (J1) results from a

competition between the two different magnetic orbital overlap pathways, viz. Cu-Oenol-

Cu and Cu-O(H)-Cu, which may have opposite face relative to each other. On the other

hand the hydroxo subunit should correspond to a moderate antiferromagnetic

superexchange interaction (J3) is due to dx2-y2⎢⎢dz2 pathway.

For the compound 17, in which the environment of the eight copper ions is

practically square pyramidal (4+1) with unpaired electron in the dx2-y2 orbital, except the

central copper ions Cu(5) is in an octahedral environment with the unpaired electron in

dz2 orbital, due to the Jahn-Teller distortion, which is evidenced in the X-ray structure.

The strong interaction mediated through alkoxo bridges in the {Cu2L}+ unit is thus well

justified and comparable to the reported25 values in the range J = -111 to -380 cm-1. The

moderately large Cu-O-Cu angles result in good overlap between the copper dx2-y2 and

alkoxo px and py orbitals. That the J2 coupling is much smaller in comparison to J1

coupling could be explained very nicely due to the countercomplementary interaction

promoted by the exogenous hydroxo group and can be compared with literature survey,

documented well.8,9b,10,25f,26-27 It is to be also mentioned that though the Cu-O-Cu angle is

very large (131°) but the interaction is reduced by the countercomplementary exchange

interaction promoted by the carboxylate group and in one case the interaction between

the copper ions mediated through alkoxo-hydroxo is ferromagnetic in nature ( J = + 17

cm-1)10 due to the countercomplementary interaction mediated through the hydroxo

bridge.

162

CHAPTER 7

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165

RARE EXAMPLES OF "NONANUCLEAR" CLUSTERS

166

Chapter 8

CHAPTER-8

CONCLUSION AND PERSPECTIVES

The attempt to design oximate based polynuclear complexes in the field of molecular

magnetism is the main goal of this work. Careful design of these polynuclear complexes has

allowed us to isolate complexes with the desirable geometry and the results have led to valuable

structural and magnetochemical insights. The main information and conclusions concerning this

work are summarized and some perspectives are suggested. To conclude, the following points of

this study deserve particular attention:

CHAPTER−2

The ligation property of a metal complex, tris(pyridine-2-aldoximato) nickel(II), has been

explored to generate heterometal complexes like NiIIMnIIINiII and NiIICrIIINiII. The

thermodynamic stability of the in-situ generated monoanion, [Ni(PyA)3]- with facially disposed

three pendent oxime oxygen atoms, makes it possible to isolate linear trinuclear complexes.

The exchange interaction between the central Mn(III) and neighboring Ni(II) is of

antiferromagnetic in nature, albeit weak, and the exchange pathway dz2⎜⎜σsp2⎜⎜d'z2 determines

the strength and sign of J for the Mn(III)•••Ni(II) pair in complex 1. On the contrary, the overall

exchange interaction for complex 2, NiIICrIIINiII, is ferromagnetic. The Cr(III)•••Ni(II)

interaction in the NiIICrIIINiII complex (2) is a classic example for intramolecular ferromagnetic

coupling, which is predominantly due to the orthogonality of the magnetic orbitals. This is in

accord with the Goodenough-Kanamori orthogonality rule as expressed by Ginsberg's symbols:

eg (NiII) ⎢⎢σNO ⊥ t2g (CrIII). It is to be emphasized here that two different exchange interactions

are operative in the linear trinuclear NiIICrIIINiII complex. The nearest neighbor exchange

interaction between Cr(III)•••Ni(II) is found to be + 0.60 cm-1, while the interaction between the

terminal Ni(II) ions is evaluated to be - 0.90 cm-1. The assumption occasionally made that no

coupling prevails between the terminal ions may yield a miss assigned ground state.

Isolation of complex 3, a triangular trinickel(II) complex, containing the neutral unit

[Ni(PyA)2(PyAH)]0, is in accord with the reported23 thermodynamic data that the neutral unit is

more stable than the mono anionic species [Ni(PyA)3]-. It must be noted in this connection that

isolation of triangular Ni(II) is very much dependent on the precipitation conditions. Our attempt

to prepare a trinickel(II) compound with the linear structure like that of 1 and 2,

Conclusions and perspectives

[NiII(PyA)3NiII(PyA)3NiII]0 starting from Nickel(II) acetate resulted in a compound consisting of

two monomeric [Ni(PyA)2(PyAH)]units held together by two O...H...O bridges.

The nickel(II) centers in the triangular unit of complex 3 are disposed as a scalene triangle

with three different Ni...Ni distances. In spite of that, an excellent fit of the experimental

magnetic moment data with an isosceles triangular model of three spins with S = 1.0 is possible,

presumably due to only two types of bridging ligands. The triplet ground state ⏐1,2> is only 8.4

cm-1 below the first excited singlet state ⏐0,1> for 3.

It has been established that the ground state is determined not by the absolute values of J

and J' but by their ratio, ρ = J'/J. For ρ ≤ 1/2, the ground state is E(1,2), and for ρ ≥ 2, is E(1,0).

On the other hand for 1/2 ≤ ρ ≤ 2, the ground state is E(0,1). As a whole, the situation may be

described as follows : the antiferromagnetic interaction between Ni(1) Ni(2) and Ni(1) Ni(3)

polarizes the spins around Ni(2) and Ni(3) in a ferromagnetic fashion. Any antiferromagnetic

interaction along Ni(2) Ni(3) opposes this effect. When ⎢J' ⎢ is small enough (ρ≤1/2), the

ferromagnetic polarization takes over. When ⎢J' ⎢ is large enough (ρ ≥ 2), the antiferromagnetic

interaction takes over. When the ferromagnetic polarization and the antiferromagnetic interaction

are of the same order of magnitude, the system looks for a compromise. The spin vectors around

Ni(2) and Ni(3) are neither parallel nor antiparallel. Particularly interesting are the two situations

ρ = 1/2 and ρ = 2. For both the cases the ground state is accidentally degenerate and the spins are

unable to decide which state to be and the system is frustrated. At this point it is really worth-

mentioning that, the ratio,

= J'/J determines the ground state in the isosceles triangular model

where all the local spins are of integer values, this important consideration was overlooked

previously, in some cases,18 led to a miss assigned spin ground state.

CHAPTER -3

The dinucleating oxime ligand acts as a backbone for the synthesis of linear tetranuclear

complexes where Me3Tacn acts as the terminal ligand. The results described in chapter-3 show

that it is possible to stabilize the tris(2,6-diformyl-4-methyl phenoldioximato) bis manganese(II)

pentaanion by complexation with the [Me3TacnMIII]3+, where M = Mn(III), Fe(III) or Cr(III)

unit. Tris(2,6-diformyl-4-methyl phenoldioximato) bis manganese(II) pentaanion is capable of

functioning as bridging ligands to give rise to linear homo- and heterotetranuclear complexes and

can mediate a varying range of exchange interactions, including weak to moderate

antiferromagnetic and even ferromagnetic exchange. Because of the quasi-isostructural nature

these materials are unique and ideally suited for the study of intramolecular exchange

interactions between the paramagnetic transition metal ions as a function of their respective dn

Chapter 8

electronic configurations. Five complexes were isolated and they are abbreviated as

BIIIMnIIMnIIBIII (4), MnIIIMnIIMnIIMnIII (5), MnIVMnIIMnIIMnIV (6), FeIIIMnIIMnIIFeIII (7)

and CrIIIMnIIMnIICrIII (8).

All the complexes exhibit overall antiferromagnetic interactions. The magnetic

susceptibility data for 4 demonstrates antiferromagnetic exchange coupling between the two

paramagnetic high-spin Mn(II) [SMn(II) = 5/2] centers. The exchange coupling constant was

evaluated to be J = - 8.4 cm-1. The evaluated value of the isotropic exchange interactions

between the central Mn(II) centers, in complex 4 was employed to extract the exchange

interactions parameter in the tetranuclear complexes 5, 6, 7 and 8. The obtained values resemble

quite satisfactorily in case of complexes 5, 7 and 8, where JMn(II)...Mn(II) were evaluated to be -

8.2 cm-1, - 8.0 cm-1 and - 8.75 cm-1 respectively. The nearest neighbor Mn(III)...Mn(II) and

Mn(IV)...Mn(II) interactions were assigned as weak ferromagnetic in nature, while the

interaction between the Fe(III)...Mn(II) and Cr(III)...Mn(II) are of weak antiferromagnetic in

nature.

Complex 6 is the first structurally characterized tris-(oximato) bridged

MnIVMnIIMnIIMnIV tetranuclear complex and the parallel spin coupling, albeit weak ( J = + 0.8

cm-1) between the neighboring Mn(IV) and Mn(II) ions, falls at the lower end of the observed

range for all similar compounds known in the literature.2 Thus the contribution of the path e'

⎢⎢sp2⎢⎢e' to the overall interaction becomes very important, since the e' orbitals centred on

Mn(IV) and Mn(II) are empty and half-filled, respectively, leading to ferromagnetic interaction.

It is interesting to note that the related isostructural CrIIIMnIIMnIICrIII complex exhibits weak

antiferromagnetic interaction (J = - 2.4 cm-1) between the nearest neighbor Cr(III) and Mn(II)

ions. Thus the contribution of the path t2g(CrIII) ⎢⎢sp2 ⎢⎢t2g(MnII) to the overall interaction

becomes important, as, this path provides antiferromagnetic contribution.

CHAPTER-4

The results described in chapter-4 reveal that heterotetranuclear butterfly complexes can be

synthesized by using “metal-complexes” as ligands. (2,6-diacetylpyridinedialdoximato) copper

(II) anion is capable of functioning as bridging ligands and by complexation with [Me3TacnM]3+,

where M = Fe(III) or Cr(III), to give rise to heterotetranuclear butterfly complexes FeIII2CuII2

(9), CrIII2CuII2 (10), where Cu(II) occupy the "body" and Fe(III) or Cr(III) occupy the "wing-tip"

positions of the butterfly.

This study confirms that there are indeed three different coupling constants, JA = Jwb, JB =

Jwb, JC = Jbb operative in the tetranuclear butterfly FeIII2CuII2 complex. Full matrix

diagonalization method produced best fit parameters, JA = Jwb = - 125.0 cm-1 and JB = Jwb = - 6.0

Conclusions and perspectives

cm-1, JC = Jbb = - 50.0 cm-1. VTVH measurement suggests that, it is indeed a high-spin molecule

with ST = 4 ground state. Simulation of the VTVH magnetic data, provides the information about

exchange coupling constants with JA = Jwb = - 125.0 cm-1 and JB = Jwb = - 6.0 cm-1, JC = Jbb = -

50.0 cm-1, DFe = + 2.7 cm-1.

Due to the presence of competing exchange interactions the ratio of the exchange coupling

constants determines the ground state, not their absolute magnitudes. The strong magnetic

interaction between the Fe(III) and Cu(II) ions can be interpreted by the combinations of the

symmetry allowed Fe(dx2-y2) ⎢⎢(O) ⎢⎢Cu(dx2-y2) and Fe(dx2-y2) ⎢⎢σNO ⎢⎢Cu(dx2-y2), π- and σ-super

exchange pathways respectively. Presence of strong Jwb over Jbb induces spin frustration in the

butterfly FeIII2CuII2 core congeners.

In order to provide a theoretical basis for the observed magnetic properties of CrIII2CuII2,

a "two-J" model was employed to fit and interpret the experimental data. Full matrix

diagonalization method produced best fit of the parameters, JA = Jwb = - 81.0 cm-1 and JB = Jwb =

- 16.0 cm-1. VTVH measurement suggests that the molecule possesses an ST = 2 ground state and

is indeed a "high-spin" molecule. Simulation of the VTVH magnetic data provides the

information about exchange coupling constants with JA = Jwb = - 81.0 cm-1 and JB = Jwb = - 16.0

cm-1. Interestingly, the coupling between the CrIII and CuII ions in 10 is antiferromagnetic in

nature in contrast to that reported9-11 for oxime bridged heteronuclear Cr(III)Cu(II) complexes

Due to the presence of competing exchange interactions the ratio of the exchange coupling

constants determines the ground state, not their absolute magnitudes. Presence of strong Jwb over

Jbb induces spin frustration in the butterfly CrIII2CuII2 core congeners. CrIII2CuII2 species

exhibits irregular spin state structure. The level ordering is a result of the mutual influence of the

two different interactions which may lead to ground state variability.

These results show that it is possible to stabilize “high-spin" ground states, due to the

molecular topology of the paramagnetic centers, despite antiferromagnetic interactions

prevailing between the spin carriers. In the light of the present state of knowledge, the strategy

of "irregular spin-state" structure resulting from particular spin topology is more effective in

obtaining "high-spin" molecules than the common strategy of obtaining ferromagnetically

coupled systems through involvement of symmetry related strict orthogonality of the magnetic

orbitals of the interacting metal centers.

CHAPTER-5

The results described in this chapter show that tetramanganese clusters with different molecular

topologies can be synthesized and led to interesting magnetic properties. The ligands Hppi and

Chapter 8

salicylaldoxime act as the backbone for the synthesis of MnII4 (11) and MnIII4 (12) complexes

respectively with different topologies like "star-shaped", "tetrahedral" etc. There are very few

examples of tetranuclear clusters with centred planar topology. The presented tetramanganese(II)

cluster with "star-shaped" geometry is one of the rare example in this area.

Complex 11 is a rare example of ferromagnetically coupled tetramanganese(II) cluster.

Detailed analysis of the temperature and field dependent magnetic behavior demonstrates a very

weak ferromagnetic interaction is operative between the central and peripheral Mn(II) ions,

which leads to high-spin ground states (ST = 10). In order to provide a theoretical basis for the

observed magnetic properties of MnII4, a "two-J" model was employed to fit and interpret the

experimental data. Full matrix diagonalization method produced best fit parameters: J12 = J13 = +

0.32 cm-1 and J14 = - 0.2 cm-1.

The high-spin Mn(II) centers with S = 5/2 exhibit weak ferromagnetic coupling in the MnII4

molecule as is evidenced from both the magnetic susceptibility and variable temperature

variable field (VTVH) measurements, yielding high-spin molecule with ST = 10 ground state.

Simulation of the VTVH magnetic data, provides the information about exchange coupling

constants with J12 = J13 = + 0.47 cm-1 and J14 = - 0.2 cm-1.

[MnIII4(salox)4(salox H)4] (12) complex is a ferromagnetically coupled "high-spin"

tetramanganese(III) cluster of tetrahedral geometry. The study also confirms that there are indeed

two different coupling constants, J12 = J23 = J34 = J14 and J14 = J23 are operative in the tetrahedral

tetramaganese(III) cluster 12. Full matrix diagonalization method produced best fits of the

parameters, J12 = J23 = J34 = J14 = + 1.9 cm-1; J14 = J23 = - 1.6 cm-1 and D1 = D2 = D3 = D4 =

⎜3⎜cm-1

The high-spin Mn(III) centers with S = 2 exhibit weak ferromagnetic coupling in the MnIII4

molecule as is evidenced from both the magnetic susceptibility and variable temperature

variable field (VTVH) measurements, yielding high-spin molecules with ST = 8 ground state.

Simulation of the VTVH magnetic data, provides the information about exchange coupling

constants with J12 = J23 = J34 = J14 = + 1.9 cm-1; J14 = J23 = - 1.6 cm-1 and D1 = D2 = D3 = D4 =

⎜3⎜cm-1.

CHAPTER-6

Magnetostructural study of two hexanuclear manganese and one hexanuclear copper clusters is

presented in this chapter. Two new hexanuclear mixed-valence, isostructural manganese

complexes 13 and 14 have been prepared from the pentadentate dapdo ligand. The hexanuclear

mixed-valence MnIII4MnII2 complexes containing the structural core [MnIII4MnII2(µ4-O)2] are

Conclusions and perspectives

rather uncommon compared to compounds with [MnII4MnIII2(µ4-O)2] core. Complexes 13 and

14 are the first structurally characterized discrete hexanuclear complexes with [MnIII4MnII2(µ4-

O)2] core congener. These two hexanuclear MnIII4MnII2 complexes represent the examples of

"edge- sharing tetrahedra".

The magnetic susceptibility data for [MnIII4MnII2(µ4-O)2] core congeners 13 and 14 exhibit

both intramolecular antiferromagnetic and ferromagnetic exchange coupling. A "four-J" model

was employed to fit and interpret the experimental data. The system may be envisaged of two

ferromagnetically coupled antiferromagnetic triangles and the fact that JA

JC clearly stabilize

a local S = 5/2 ground state in each triangular unit, the ferromagnetic pathway JD leads to an ST

= 5 ground state. So it is a "high-spin" molecule and ST = 5 is also evidenced from the variable-

temperature-variable field (VTVH) magnetic measurements.

By using the ITO mathematical approach the exchange interaction was found to be JA = -

12.6 cm-1, JB = - 4.6 cm-1, JC = + 2.4 cm-1, JD = + 1.9 cm-1, gMn = 1.98, D1 = D3 = D5 = D6 =

DMn(III) = 4.0 cm-1. The exchange interaction between Mn(III)...Mn(III) is antiferromagnetic in

nature, while the interactions between Mn(III)...Mn(II) [d4(HS)/d5(HS)] were found to be both

antiferromagnetic and ferromagnetic, albeit weak, as the average MnIII-O-MnII bond angle of

100° prevents the better overlap between the magnetic orbitals. This gives rise to ferromagnetic

exchange interaction (JB).

The main lesson from this study is that high nuclearity Mnx complexes can be prepared

which have either pairwise ferromagnetic MnII...MnIII or MnIII...MnIII interactions or a

combination of pairwise antiferromagnetic interactions or in the third possibility combination

of pairwise ferromagnetic-antiferromagnetic interactions that lead to molecules with ST ≠ 0

ground state. Based on combination of pairwise exchange interactions, competing exchange

interaction, and topology the polynuclear manganese complexes are stabilized in high-spin

ground states.

The hexadentate oxime ligand generates a new hexanuclear copper(II) cluster(15),

consisting two linked Cu3O core. Several trinuclear copper(II) structures with central O2- or

OH- groups have been structurally characterized, however this structure with two such triangles

linked by a proton appears to be novel.

The oximate ligands generally mediate strong antiferromagnetic exchange coupling

between the d9 copper(II) ions with a dx2-y2 ground state as each copper(II) ions are in a square

pyramidal coordination environment. The simulation of the magnetic data affords an

antiferromagnetic exchange interaction in complex 15, in accordance with the large Cu-O-Cu

angles of 113.65 and 114.32° respectively in each triangular unit. A "two-J" model was used to

Chapter 8

analyze the magnetic data. From the best fit, the intra-and interdimer antiferromagnetic

exchange coupling constants are obtained to be JA = - 614.1 cm-1 and JB = - 114.5 cm-1

respectively. The overall coplanar Cu3O core structure permits larger magnetic exchange

interaction. As both the oximate and oxo groups transmit strong exchange coupling between the

copper(II) ions, the overall effect of both of these transmissions is reflected in strong

antiferromagnetic exchange interaction in this hexanuclear copper(II) cluster. Values of J ∼ -

1000 cm-1 have been reported for other imino-oximate complexes.

CHAPTER-7

This chapter describes the structure and magnetic properties of two rare examples of

nonanuclear copper(II) and nickel(II) clusters. Two new nonanuclear nickel(II) (16) and

copper(II) (17) complexes have been isolated with the ligand syn-2-pyridinealdoxime and N,N'-

(2-hydroxypropane-1,3-diyl)bis(benzoylacetoneimine) respectively.

Chemically significant hydrogen bonding may stabilize the nonanuclear NiII cluster. The

magnetic susceptibility data for 16 exhibits an antiferromagnetic coupling between the

paramagnetic Ni(II) (SNi = 1) centers and gives rise to ST =1 ground state. Antiferromagnetic

exchange coupling is mediated through an average Ni(II)....Ni(II) separation of 3.38 Å . A close

examination of the structure indicates that there are five different types of bridging groups for

transmission of exchange coupling between the Ni(II) centers with SNi = 1.0 : i) diatomic -NO-,

ii) µ3-oximate -N-O, iii) µ2-OH, iv) µ3-OH , and v) µ2-OH2. Two avoid overparametarization a

"two-J" model was employed to simulate the experimental magnetic data and

resulted in moderate antiferromagnetic exchange interaction of the value J1 = - 26.5 cm-1 and J2

= - 7.0 cm-1. The stronger J1 interaction through the diatomic NO-bridging as oppose to J2

interaction mediated through the µ3-oximate oxygen is in accord with the literature. This is the

second example of the magnetostructurally characterized nonanuclear nickel(II) cluster. The

ZFS (D) parameter of the ST = 1 ground state is found to be DS = 1 = + 2.7 cm-1.

The polynuclear copper(II) cluster (17) is a rare example of magnetostructurally

characterized [CuII9(OH)4]14+ core congener. This cluster has a novel metallamacrocyclic core

which is generated from the self-assembly process. The magnetic susceptibility data for CuII9

complex exhibits overall antiferromagnetic coupling between the copper(II) centers and result

in a non-diamagnetic ground state.

This complex also belongs to the class of irregular spin state structure, as is evidenced

from the minima observed in the magnetic susceptibility plot. This is due to the presence of

competing exchange interactions between the spin carriers.

Conclusions and perspectives

To avoid the over-parameterization, three different exchange coupling constants were

taken into consideration and from the best fit, the values: J1 = - 189.1 cm-1, J2 = - 22.7 cm-1, J3 =

- 45.7 cm-1 are obtained. J1, J2 and J3 define the exchange interactions between the copper(II)

ions mediated through alkoxo, alkoxo-hydroxo and hydroxo bridges respectively. As expected,

the magnetic response of compound 17 is dominated by the strong antiferromagnetic exchange

interaction through the alkoxo bridge in the {Cu2L}+ unit which shows large Cu-O-Cu bond

angles. J2 coupling constant is much smaller in comparison to J1 coupling and could be

explained very nicely due to the countercomplementary interaction promoted by the exogenous

hydroxo group.

Magnetostructural Correlation:

In the last few years, the idea of synthesizing polynuclear complexes involving "metal-

oximates" as building blocks has become quite popular. In the near future new chemistry is

expected to be developed that enables chemists to synthesize a wide variety of the ligands

possessing the versatility of the functioning both as bridging and polynucleating group. Thus,

larger polynuclear assemblies are expected to be synthesized through modular approaches by

choosing suitable ligands. The ultimate goal, obviously, is the development of the area of

molecular magnetism. Oximate groups can mediate exchange interactions of varying range,

weak and moderate ferromagnetic to strong antiferromagnetic. A problem concerning such

exchange coupled systems is the lack of availability of isostructural polynuclear complexes

with varying dn electron configurations. Investigation of a series of isostructural polynuclear

complexes will be much more informative compared to those comprising singly isolated

exchange coupled clusters only. Although most of the compounds discussed in this work, along

with the structurally characterized oximate based polynuclear complexes reported earlier, little

can be said about the magnetostructural trends. This thesis is focused on such exchange

coupled polynuclear complexes containing the bridging core M-N-O-M' originating from metal

oximates. Qualitative rules allowing the prediction of the nature of interaction between two

spin carriers according to the symmetry of the magnetic orbitals were proposed in the 1950's by

Goodenough and Kanamori. The concepts of natural orbital and overlap integral allow the

generalization and extension of Goodenough-Kanamori rules. However, no such relation have

been established between the exchange coupling constant and the metrical parameters of the

diatomic bridge like oximate(N-O), azine (N-N) or oxalate. Discussion, in detail, needs to be

concentrated on such system where considerable structural and magnetochemical work have

been reported. This thesis concentrates one of such parameter, e.g. the role of the dihedral angle

Chapter 8

comprising the planes between M-N-O and O-N-M' in exchange interaction and such work is

worth doing. In other words, it appears tedious, if not impossible, to extract a qualitative

understanding of the relation between dihedral angle and exchange interaction. Table 8.1

summarizes dihedral angle comprising the planes between the planes M(O-N) and (O-N)M’

and the exchange coupling constant of some magnetostructurally characterized oximato based

polynuclear complexes irrespective of nuclearity.

Table 8.1: Magnetostructural parameters of some oximato complexes

Compounds Average

dihedral angle

between the

planes

comprising

M-O-N and

O-N-M' atoms

Exchange

coupling

constants

References :

1. [(Me3Tacn)MnIIIMnII(PyA)3]2+ 32.8 + 1.6 i

2. [(Me3Tacn)MnIII(dmg)3MnIIMnIII(Me3Tacn)]2+ 13.3 + 4.7 ii

3. [(Mcoe)3MnIIMnIIIMnII(Mcoe)3]+ 9.3 -1.3 iii

4. [(TapTacn)MnII(µ-O2COMe)MnIIIMnII(TapTacn)]+ 2.1 + 2.0 iv

5. [(Me3Tacn)MnIIIMnII(dfmp)3MnIIMnIII(Me3Tacn)]+ 30.3 + 2.8 Complex 5

6. [MnIIMnIVMnII(pko)4(OMe)2(OCN)2] 3.75 + 4.1 v

7. [MnIIMnIVMnII(pko)4(OMe)2(Cl)2] 14.8 + 3.9 v

8. [(Me3Tacn)MnIVMnII(dfmp)3MnIIMnIV(Me3Tacn)]3+ 17.0 + 0.8 Complex 6

9. [MnIIMnIVMnII(pko)4(OMe)2(SCN)2] 34.3 + 3.1 vi

10. [(Me3Tacn)FeIII(dmg)3MnIIFeIII(Me3Tacn)]2+ 4.8 - 6.7 vii

11. [(Me3Tacn)FeIIIMnII(PyA)3]2+ 32.1 - 6.1 viii

12. [(Me3Tacn)FeIIIMnII(dfmp)3MnIIFeIII(Me3Tacn)]+ 29.8 - 1.8 Complex 7

13. [(Me3Tacn)CrIIIMnII(PyA)3]2+ 31.4 + 1.5 ix

14. [(Me3Tacn)FeIII(µ-O..H..O-µ)CuII2

(dapdo)2(µ-Cl) FFeIII(Me3Tacn)]2+

5.7 - 125.0 Complex 9

15. [(Me3Tacn)CrIII(dmg)3CuIICrIII(Me3Tacn)]2+ 9.1 + 18.5 x

16. [(Me3Tacn)CrIII(OMe)CuII(dopn)(H2O)]2+ 21.8 + 18.5 xi

17. [(Me3Tacn)CrIIICuII(PyA)3]2+ 34.0 + 1.8 xii

18. [(Me3Tacn)CrIII(µ-OH)2CuII2

(dapdo)2(Br2) CrIII(Me3Tacn)]2+

76.7 - 16.0 Complex 10

19. [(Me3Tacn)FeIIICuII(PyA)3]2+ 32.1 - 42.5 viii

Conclusions and perspectives

20. [(Me3Tacn)FeIII(dmg)3CuIIFeIII(Me3Tacn)]2+ 10.6 - 53.0 xx

21. [(Me3Tacn)MnIII(OOCMe)CuII(dopn)]2+ 24.5 + 54.0 xi

22. [(Me3Tacn)MnIII(dmg)3CuIIMnIII(Me3Tacn)]2+ 26.5 - 63.0 ii

23. [(Me3Tacn)FeIII(Cl)CuII(MeOH)NiII(MeOH)2(LOX)]2+ 47.1 - 19.8 xii

24. [(Me3Tacn)FeIIINiII(dfmp)2NiII(MeCOO)2

(MeOH)2FeIII(Me3Tacn)]2+

31.1 - 6.8 xxi

25. [(Me3Tacn)FeIII(dmg)3NiIIFeIII(Me3Tacn)]2+ 24.1 - 32.0 xxii

26. [(Me3Tacn)FeIII(NCS)NiII(H2O)(NCS)

NiII(NCS)2(H2O)(LOX)]

28.2 - 9.3 xiii

27. [(Me3Tacn)FeIIINiII(PyA)3]2+ 39.5 - 34.0 viii

28. [(PyA)3NiIIFeIIINiII(PyA)3]+ 38.4 - 31.0 xiv

29. [(Me3Tacn)CrIIINiII(PyA)3]2+ 38.8 - 9.2 ix

30. [(Me3Tacn)CrIIINiII(PPyA)3]2+ 20.8 0.0 ix

31. [(Me3Tacn)CrIII(dmg)3NiIICrIII(Me3Tacn)]2+ 25.9 - 0.7 x

32. [(PyA)3NiIICrIIINiII(PyA)3]+ 35.2 + 0.6 Complex 2

33. [{Ni(Dien)}2(µ3-OH)2{Ni2(Moda)4}]2+ 7.2 - 20.3 xv

34. [Ni4(MeOH)2(pko)6]2+ 36.5 -24.0 xvi

35. [(Me3Tacn)Ni2(PyA)3]2+ 43.1 - 33.0 xvii

36. [Ni3(PyA)5(PYAH)]+ 24.1

75.8

-8.3

-2.0

Complex 3

37. [Ni4(TapHTacn)3]2+ 36.4 -13.4 iv

38. [Ni6(amox)6(µ6-O)(µ3-OH)2]2+ 44.0 -25.0 xix

39. [Ni3(Dtox)(Dtox H)2]2+ 37.5

58.0

-14.0

-7.3

xviii

The obvious question is: can we find some relation between these parameters? The

results obtained are summarized below:

(a) When we consider dihedral angle and exchange coupling constants in a general

manner, we can not find any correlation. Figures 8.1a and b show such plots where

little can be said about the influence of the dihedral angles on exchange interaction.

Chapter 8

(a) (b)

Figure 8.1: Plot of dihedral angles comprising the planes between M(O-N) and (O-N)M' and

exchange coupling constant (J)

(b) When we consider each individual pair, it seems that there is certain influence of

the dihedral angles on exchange interactions.

According to Kahn, Goodenough and Kanamori CrIIINiII [d3d8(octahedral)], CrIIICuII

[d3d9(octahedral)], and MnIVMnII [d3d5(HS)(octahedral)] interactions are expected to be

ferromagnetic due to the t2g⊥ e

g magnetic orbitals as several strictly ferromagnetic

paths are available..

(a) (b)

Figure 8.2 : Plot of dihedral angles comprising the planes between MnIV(O-N) and (O-N)MnII and

exchange coupling constant (J) (a) and dihedral angles comprising the planes between Cr(O-N)

and (O-N)Cu and exchange coupling constant (J) (b)

0 5 10 15 20 25 30 35

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

J (cm-1)

H = - 2JSiSj

Dihedral angle between MnIV(O-N) and (O-N)MnII

0 1020304050607080

-20

-15

-10

-5

J (cm-1)

H = - 2JSiSj

Dihedral angle between CrIII(O-N) and (O-N)

15 16

CuII

0 1020304050607080

-60

-40

-20

J (cm-1)

H = - 2JSiSj

Dihedral angle between

15 16

20 21

0 5 10 15 25 30

-8

-6

-4

-2

20 35

J (cm-1)

H = - 2JSiSj

Dihedral angle between O-N) and (O-N)

10 11

M = Mn,Fe, Cr

O-N) and (O-N)Cu

Conclusions and perspectives

Figures 8.2 and 8.3 suggest that there is a decreasing tendency of ferromagnetic

exchange coupling constants with increasing dihedral angles. This observation leads us

to the conclusion that with increasing dihedral angle there may be some deviation from

orthogonality, which in turn, causes better overlap between the magnetic orbitals results

and is reflected in increasing antiferromagnetic coupling with increasing dihedral angle.

Deviation from such behavior of the complexes 16 and 32 may be due to the influence

of subtle coordination differences around metal centers.

0 5 10 15 20 25 30 35

-2

-1

0 5 10 15 20 25 30 35

J (cm-1)

H = - 2JSiSj

Dihedral angle between

20 22 24 26 28 30 32 34 36 38 40

-10

-8

-6

-4

-2

J (cm-1)

H = - 2JSiSj

Dihedral angle between

(a) (b)

Figure 8.3: Plot of dihedral angles comprising the planes between Cr(O-N) and (O-N)Ni and

exchange coupling constant (J)

The similar trend is also observed in case of MnII…MnIII cases. However MnII...MnIII

exchange interaction value of J = - 1.3 cm-1 in 3, which results from Mn(III)-O-N-

Mn(II) superexchange pathways can be compared with the related dimethylgyoximato

(2), diformyl-4 methylphenoldioximato (5) and pyridinealdoximato(1)- bridging in the

work of Birkelbach, compound 5 and Chaudhuri and co-workers in which

Mn(II)...Mn(III) interactions were found to be ferromagnetic. The difference of sign of

these Mn(II)-N-O-Mn(III) interaction results from the net effect of the ferromagnetic

and antiferromagnetic contributions to JMn(II)...Mn(III) Which, in turn, will be influenced

by subtle coordination differences on the Mn(III) and Mn(II) centers, and to a lesser

degree by the terminal bridging groups. Linear trinuclear MnIIMnIIIMnII congener (4)

does not fit in the trends. Careful examination reveals that the exchange coupling in this

complex mediated mainly by two-types of bridges, a single atom -O-bridge and a two

CrIII(O-N) and (O-N)

NiII MnIII (O-N) and (O-N)MnII

Chapter 8

atom N-O linkage, of which the later contribution is expected to be small. The angle at

the bridging oxygen would be expected to be important, this affects the nature of σ and

π overlap between the metal magnetic orbitals and the oxygen px, py and pz orbitals

mediate the exchange. Mn(1)II-O-Mn(2)III and Mn(2)III-O-Mn(3)II angles are 97.5 and

108° respectively. However, the magnetic response in this complex was analyzed by

using a "one-J" mode, which is not strictly true. So a "two-J" model seems to be more

appropriate and Mn(1)II...Mn(2)III interactions is expected to be more ferromagnetic

compared to the exchange interaction between Mn(3)II...Mn(2)III.

From the above observation it can be concluded that with increasing dihedral angle

antiferromagnetic exchange interaction increases.

increase of dihedral angle and the observed result is opposite compared to that of

previous one. Fe(III)...Cu(II) is expected to be antiferromagnetic due to presence of

several antiferromagnetic paths in the exchange coupling constant. Reduction of

antiferromagnetic exchange coupling constant suggests that lesser overlap is prevailing

between the magnetic orbitals with increasing angle.

0 1020304050

-140

-120

-100

-80

-60

-40

-20

J (cm-1)

H = - 2JSiSj

Dihedral angle between

FeIII(CuII

O-N) and (O-N)

Figure 8.4: Plot of dihedral angles comprising the planes between Fe(O-N) and (O-N)Cu and

exchange coupling constant (J)

(d) In the Ni-N-O-Ni case little can be said about the trends, but it can be concluded that

the interaction through diatomic NO bridge is stronger than the interaction mediated

through µ3-oximate oxygen. Comparison of exchange coupling constants in complexes

Conclusions and perspectives

34, 35, 36, 37 and 38 reveals that each oximate (NO) may transmit J = - 10.5 ± 1.5 cm-1

antiferromagnetic exchange coupling. While comparison of the exchange coupling

constants in the FeIII-O-N-NiII complexes reveal that each oximate may transmit J = ∼ -

11cm-1 antiferromagnetic exchange interaction irrespective of the dihedral angles.

Summarizing some of the results of the exchange-coupled oximate -bridged polynuclear

complexes reported in the literature, along with some of the complexes in this work, it

appears that no strong correlation between structural and magnetic properties for such

complexes has been obtained. Hence obtaining any such correlation requires

isostructural purely octahedral dinuclear complexes. The importance of designed

synthesis lies there in.

Perspectives:

A few ideas and perspectives, in the continuation of this work are outlined below:

(1) Synthesis and magnetostructural characterization of linear trinuclear MnIIMnIIIMnII

complex of syn-2-pyridinealdoxime ligand, isostructural with the complexes 1 and 2

need to be explored.

(2) Experimental determination of the exchange coupling constant for complex 4 by

using X- and Q-band EPR techniques and comparison of the values obtainable from

spectroscopic technique with the evaluated value from SQUID measurement.

(3) HFEPR measurement of the complex 9 (FeIII2CuII2) to verify the ground state of the

cluster.

(4) Alternating current (AC) susceptibility measurement of the MnII4 complex (11), to

check whether this complex can be a single molecule magnet (SMM).

(5) AC-susceptibility and HFEPR measurement of the complex 12 (MnIII4) to verify the

ground state of the complex and for the precise determination of the sign and

magnitudes of zero-field splitting parameter (D).

(6) AC-susceptibility measurement of the complex 14 (MnIII4MnII2), for the precise

determination of the sign and magnitude of the zero-field splitting parameter and to

check SMM properties.

(7) Synthesis and magnetostructural characterization of the CrIII4 and VIII4 core

congeners isostructural with MnIII4 (12)

(8) In traversing the first-row d-block elements we have noticed that paramagnetic Ti

and V-oximates remain relatively unexplored, probably because of difficulties in

Chapter 8

synthesis and stability. Clearly, these aspects need to be further experimentally

explored.

References:

(i) P. Chaudhuri and U. Flörke, Unpublished result.

(ii) F. Birkelbach, U. Flörke, H-J. Haupt, C. Butzlaff, A. X. Trautwein, K. Wieghardt

and P. Chaudhur, Inorg. Chem., 1998, 37, 2000

(iii) D. J. Price, S. R. Batten, K. J. Berry, B. Moubaraki and K. S. Murray, Polyhedron,

2003, 22, 165

(iv) V. Pavlischuk, F. Birkelbach, T. Weyhermüller, K. Wieghardt and P. Chaudhuri,

Inorg. Chem., 2002, 41, 4405

(v) M. Alexiou, C. M. Zeleski, C. Dendrinou-Samara, J. Kampf, D.P. Kessissoglou, V.

L. Pecoraro, Z. Anorg. Allg.Chem., 2003, 629, 2348

(vi) M. Alexiou, C. Dendrinou-Samara, A. Kasagianni, S. Biswas, C. M. Zeleski, J.

Kampf, D. Yoder, J. E. Penner-Hahn, V. L. Pecoraro, D.P. Kessissoglou, Inorg. Chem.,

2003, 42, 2185

(vii) P. Chaudhuri and U. Flörke, Unpublished result.

(viii) S. Ross, T. Weyhermüller, E. Bill, E. Bothe, U. Flörke, K. Wieghardt and P.

Chaudhuri, Eur. J. Inorg. Chem., 2004, 984

(ix) S. Ross, T. Weyhermüller, E. Bill, K. Wieghardt and P. Chaudhuri, Inorg. Chem.,

2001, 40, 6656

(x) D. Burdinski, F. Birkelbach, T. Weyhermüller, U. Flörke, H-J. Haupt, M. Lengen, A.

X. Trautwein, E. Bill, K. Wieghardt and P. Chaudhuri, Inorg. Chem., 1998, 37, 1009

(xi) F. Birkelbach, M.Winter, U. Flörke, H-J. Haupt, C. Butzlaff, M. Lengen, E. Bill, A.

X. Trautwein, K. Wieghardt and P. Chaudhuri, Inorg. Chem., 1994, 33, 3990

(xii) C. N. Verani, T. Weyhermüller, E. Rentschler, E. Bill and P.Chaudhuri, J. Chem.

Soc., Chem. Commun., 1998, 2475

(xiii) C. N. Verani, E. Rentschler, T. Weyhermüller, E. Bill and P. Chaudhuri, J. Chem.

Soc.,Dalton Trans., 2000, 4263

(xiv) P. Chaudhuri and T. Weyhermüller, Unpublished result

(xv) V. V. Pavlischuk, S. V. Kolotilov, A. W. Addison, M. J. Prushan, D. Schollmeyer,

L. K. Thompson and E. A. Goreshnik, Angew. Chem. Int. Ed., 2001, 40, 4734

(xvi) M. Alexiou, C. Dendrinou-Samara, C. P. Raptopoulou, A. Terzis, V. Tangoulis and

D. P. Kessisoglou, Eur. J. Inorg. Chem., 2004, 3822

Conclusions and perspectives

(xvii) P. Chaudhuri, T. Weyhermüller, R. Wagner and S. Khanra, Unpublished result

(xviii) V. V. Pavlischuk, S. V. Kolotilov, A. W. Addison, M. J. Prushan, R. J. Butcher

and L. K. Thompson, Inorg. Chem., 1999, 38, 1759

(xix) Y-B. Jiang, H-Z. Kou, R-J. Wang and J. Ribas, Inorg. Chem., 2005, 44, 709

(xx) P. Chaudhuri, M. Winter, P. Fleischhauer, W. hasse, U. Flörke and H-J. Haupt, J.

Chem. Soc., Chem. Commun., 1990, 1728

(xxi) C. Krebs, M.Winter, T. Weyhermüller, E. Bill, K.Wieghardt and P.Chaudhuri, J.

Chem. Soc., Chem. Commun., 1995, 1913

(xxii) P. Chaudhuri, M. Winter, B. P. C. Della Vedova, P. Fleischhauer, W. hasse, U.

Flörke and H-J. Haupt, Inorg. Chem., 1991, 30, 4777

(xxiii) (a) H. Saarinen and M. Orama, Acta Chem. Scand., 1998, 52, 1209; (b) M.

Orama, H. Saarinen and J. Korvenranta, Acta Chem. Scand., 1989, 43, 407

CHAPTER 9

CHAPTER- 9

EQUIPPMENT AND EXPERIMENTAL WORK

9.1 METHODS AND EQUIPMENTS

All the analyses were performed at the Max-Planck-Institut für Bioanorganische Chemie,

Mülheim an der Ruhr, unless otherwise mentioned. Commercial grade chemicals were

used for the synthetic purposes and solvents were distilled and dried before use.

Infrared Spectroscopy

Infrared spectra were measured from 4000 to 400 cm-1 as KBr pellets at room

temperature on a ‘Perkin-Elmer FT-IR-Spectrophotometer 2000’.

NMR Spectroscopy

1H- and 13C- NMR spectra were measured using a ‘Bruker ARX 250, DRX 400 or DRX

500’. The spectra were referenced to TMS, using the 13C or residual proton signals of the

deuterated solvents as internal standards.

Mass Spectroscopy

Mass spectra in the Electron Impact mode (EI; 70 eV) were recorded on a Finnigan MAT

8200 mass spectrometer. Only characteristic fragments are given with intensities. The

spectra were normalized against the most intense peak having intensity 100. Electron

Spray Ionization (ESI) mass spectra were recorded either on a Finnigan Mat 95

instrument or a Hewlett-Packard HP 5989 mass spectrometer. ESI- and EI- spectra were

measured by the group of Dr. W. Schrader at the Max-Planck-Institute for Coal Research,

Mülheim an der Ruhr.

Elemental Analysis

The determination of the C, H, N and metal content of the compounds was performed by

the ‘Mikroanalytischen Labor H. Kolbe’, Mülheim an der Ruhr, Germany.

UV-VIS Spectroscopy

UV-VIS spectra were recorded on a ‘Perkin-Elmer UV-VIS Spectrophotometer Lambda

19’or on a Hewlett-Packard HP 8452A diode array spectrophotometer in the range 200-

1200 nm. For UV-VIS spectro-electrochemical investigations the HP 8452A diode array

spectrophotometer was used, by employing a coulometry cuvette and Bu4NPF6 as

supporting electrolyte.

EQUIPMENT AND EXPERIMENTAL WORK

Electrochemistry

Cyclic voltammetry, square wave voltammetry and linear sweep voltammetry

experiments were performed using an ‘EG&G Potentiostat / Galvanostat 273A’. A

standard three-electrode-cell was employed with a glass-carbon working electrode, a

platinum-wire auxiliary electrode and Ag/AgCl (saturated LiCl in EtOH) reference

electrode. Measurements were made under an inert atmosphere at room temperature. The

potential of the reference electrode was determined using Fc+/Fc as the internal standard.

Magnetic Susceptibility Measurements

The measurements of the temperature or field dependent magnetization of the sample

were performed in the range 2 to 290 K at 1, 4 or 7 T on a ‘Quantum Design SQUID-

Magnetometer MPMS’. The samples were encapsulated in gelatin capsules and the

response functions were measured four times for each given temperature, yielding a total

of 32 measured points. The resulting volume magnetization from the samples had its

diamagnetic contribution compensated and was recalculated as volume susceptibility.

Diamagnetic contributions were estimated for each compound by using Pascal’s

constants. The experimental results were fitted with the program JULIUS calculating

through full-matrix diagonalization of the Spin-Hamiltonian. The following Hamiltonian-

operators were used:

HZE = µB∑ gi Ŝi .B

HHDVV = -2 ∑ Jij Ŝi . Ŝj

HZFS = ∑Di[Ŝiz2-{Si(Si+1)/3}+ Ei/Di(Ŝix2- Ŝiy2)]

Indexes i,j indicate individual spins. For the magnetic measurement the calculated g

values obtained during simulation is the isotropic.

EPR Spectroscopy

First derivative X-Band EPR spectra of powdered or frozen solution samples were

measured with a ‘Bruker ESP 300 Spectrometer’ coupled to an ‘Oxford Instruments ESR

910-Cryostat’.

57Fe-Mössbauer Spectroscopy

57Fe-Mössbauer spectra were measured with an Oxford Instruments Mössbauer

spectrometer in the constant acceleration mode. 57 Co/Rh was used as the radiation

source. The minimum experimental linewidths were 0.24 mm/s. The temperature of the

sample was controlled by an ‘Oxford Instruments Variox Cryostat’. Isomer shifts were

determined relative to α-iron at 300K. The measurements were carried out at 80K and

100K with solid samples containing the isotope 57Fe.

CHAPTER 9

Crystallography

X-ray diffraction data were collected on an ‘Enraf-Nonius CAD4 Diffractometer’ or on a

‘Siemens Smart System’. Graphite-monochromatized Mo-Kα with λ = 0.71073 Å was

employed. Data were collected by the 2θ-ω scan method (3≤2θ≤50°). The data were

corrected for absorption and Lorenz polarization effects. The structures were solved by

direct methods and subsequent Fourier-difference techniques, and refined anisotropically

by full-matrix least-squares on F2 with the program SHELXTL PLUS. Hydrogen atoms

were included at calculated positions with U < 0.08 Å2 in the last cycle of refinement.

GC / GC-MS Analysis

GC of the organic products were performed either on HP 6890 instruments using RTX-5

Amine 13.5 m S-63 columns respectively. GC-MS was performed using the above

column coupled with a HP 5973 mass spectrometer with mass selective detector.

9.2 SYNTHESIS

Me3TacnFeCl3, 1 Me3TacnCrBr32, [Cu(dapdoH2)](ClO4)23 and the ligand, 2-hydroxy-

1,3-propanediylbis(benzoylacetoneimine)4 (L2H3) were prepared according to the

literature procedure.

9.2.1 LIGANDS

2,6-Diacetylpyridine dioxime [dapdoH2]

This synthesis is a modification of Hartkamp's method. 2,6-Diacetylpyridine (2.9 g, 18

mmol) was dissolved in MeOH (35 cm3), a solution of hydroxylamine hydrochloride (2.8

g, 40 mmol) and NaOH (1.6 g, 40 mmol) in MeOH:H2O (20 cm3, 1:1 by vol) was

prepared and added to the diacetylpyridine solution. The resulting solution was refluxed

with stirring for 2 h. A white precipitate began to form after 5 min heating. After 2 h, the

mixture was cooled in ice and the white precipitate was collected by suction filtration and

recrystallized from MeOH. 1H NMR (CD3COCD3, 80 MHz): δ 2.32 (6H, s, CH3), 7.71

(1H, t, Py-4H), 7.85 (1H, d, Py-3H), 10.64 (2H, s, NO-H). MS: m/z 193 (M+, 100 %).

Yield: 3.16 gm (92 %), MP: 236°C

Molecular Weight: 193 g/mol C9H11N3O2

EQUIPMENT AND EXPERIMENTAL WORK

Elemental Analysis:

%C %H %N

Calculated 55.96 5.7 21.76

Found 55.9 5.6 21.73

Infrared Spectrum:

5001000150020002500300035004000

cm -1

Synthesis of 2,6-Bis-iminomethyl-(4,6-di-tertbutyl-2-iminophenol)-4-methyl-phenol

(H3dfmp)

2,6-Diformyl-4-methylphenol was synthesized as described in ref. The corresponding

dioxime, H3dfmp, was prepared in the following way: To a suspension of 2,6-diformyl-4-

methylphenol (3.36 g; 20 mmol) and NH2OH•HCl (3.13 g; 50 mmol) in water (45 ml),

warmed at 80oC, was added methanol with stirring until a clear orange solution was

obtained. The solution was stirred at 80oC for 1 h. The solution was cooled to room

temperature, followed by addition of enough water, so that the solution just started to

become turbid. After keeping it at ambient temperature for ca. 24 h, the crystalline solid

was removed by suction filtration, washed thoroughly with water and dried in air. The

dioxime can be recrystallized from a methanol-water mixture. IR (KBr, medium and

strong selective bands only): 3380, 3329, 1623, 1604, 1465, 1307, 1265, 1061, 1027, 934,

793, 757, 696 cm-1. 1H NMR (CD3OD, 80 MHz): δ 2.34 (3H, s, CH3), 7.37 (2H, s, Ar),

8.37 (2H, s, oxime). 13C NMR (CDCl3): δ 20.31 (ArCH3), 119.78, 129.84, 130.85 (C-

Ring), 149.17 (CN), 154.48 (C-OH). MS: m/z 194 (M+, 100 %).

CHAPTER 9

Yield: 4.5 gm (70 %), MP: 186-188 °C

Molecular Weight: 194 C9H10N2O3

Elemental Analysis:

%C %H %N

Calculated 55.67 5.15 14.43

Found 55.7 5.2 14.3

Infrared Spectrum:

5001000150020002500300035004000

cm-1

9.2.2 COMPLEXES:

Synthesis of [NiII(PyA)3MnIII(PyA)3NiII](ClO4) (1)

To a light green solution of NiCl2 .6H2O (0.47 g; 2 mmol) and Mn(ClO4)2 .6H2O (0.46 g;

1 mmol) in distilled methanol (25 ml), solid pyridine-2-aldoxime(0.72g; 6 mmol) was

added with stirring, followed by addition of 7 ml of [Bu4N][OCH3] (20% in CH3OH).

The resulting red brown solution was stirred for 0.5 h and filter to procure red-brown

microcrystalline solid. X-ray quality crystals were obtained from a dimethylformamide

solution, in which methanol was allowed to diffuse.

Yield: 830 mg (81 %)

Molecular Weight: 998.49 C36H30ClMnN12Ni2O10

EQUIPMENT AND EXPERIMENTAL WORK

Elemental Analysis:

%C %H %N %Ni %Mn

Calculated 43.43 3.04 16.88 11.8 5.22

Found 43.3 3.0 16.9 11.9 5.1

Infrared Spectrum:

5001000150020002500300035004000

cm-1

Synthesis of [NiII(PyA)3CrIII(PyA)3NiII](ClO4) (2)

To a light green solution of NiCl2 .6H2O (0.47 g; 2 mmol) and Cr(ClO4)3 .6H2O (0.46 g;

1 mmol) in distilled methanol (25 ml), solid pyridine-2-aldoxime(0.72g; 6 mmol) was

added with stirring, followed by addition of 7 ml of [Bu4N][OCH3] (20% in CH3OH).

The resulting red brown solution was stirred for 0.5 h and filter to procure red-brown

microcrystalline solid. X-ray quality crystals were obtained from a dimethylformamide

solution, in which methanol was allowed to diffuse.

Yield: 720 mg (73 %)

Molecular Weight: 995.59 C36H30ClCrN12Ni2O10

Elemental Analysis:

%C %H %N %Ni %Cr

Calculated 43.43 3.04 16.88 11.8 5.22

Found 43.3 3.0 16.9 11.9 5.1

CHAPTER 9

Infrared Spectrum:

5001000150020002500300035004000

cm-1

Synthesis of [NiII3(PyA)5((PyAH)](ClO4). CH3CN (3)

Solid pyridine-2 aldoxime (0.36 g; 3 mmol) was added to a solution of Ni(ClO4)2.

6H2O(0.55 g; 1.5 mmol) in methanol(25mL) to yield a deep brown solution. 4.5 ml of

[Bu4N][OCH3] (20% in CH3OH) were added, which upon stirring yielded a red brown

solution. After 0.5 h stirring the precipitated red brown microcrystalline substance was

filtered and air dried. X-ray quality deep red-brown crystals were obtained from a

solution of 8 in CH3CN.

Yield: 550 mg (53 %)

Molecular Weight: 1044.36 C38H34ClN13Ni3O10

Elemental Analysis:

%C %H %N %Ni

Calculated 43.7 3.28 17.44 16.86

Found 43.8 3.4 17.6 17.0

EQUIPMENT AND EXPERIMENTAL WORK

Infrared Spectrum:

5001000150020002500300035004000

cm-1

Synthesis of [(CH3)B{(dfmp)3MnIIMnII{B(CH3)] (Et3NH) (4)

To a solution of H3dfmp (300 mg, 1.5 mmol) and Mn(ClO4)2. 6H2O (370 mg, 1

mmol) in methanol (40 ml) was added triethylamine (0.6 ml, 4.5 mmol) and the

suspension was stirred 10 min. To this dark solution methylboronic acid [CH3B(OH)2],

(60 mg, 1 mmol) was added. The solution was stirred at ambient temperature for 0.5 h in

the air, after which the precipitated deep yellowish solid was collected by filtration and

air-dried. The yellowish solid was recrystallized from a solvent mixture of

dichloromethane-ethanol (2:1). IR (KBr, cm-1): 1610, 1593, 1580, 1450, 1305, 1208,

1047, 1008, 946, 935, 833, 761, 738, 705. ESI-MS (m/z): 735 (100 %).

Yield: 290mg (40%)

Molecular Weight: 883.33 C37H49N7O10B2Mn2

Elemental Analysis:

%C %H %N %Mn

Calculated 50.18 5.14 11.7 13.15

Found 49.8 4.85 11.56 13.19

CHAPTER 9

Infrared spectrum:

5001000150020002500300035004000

cm-1

Synthesis of [(Me3Tacn)MnIII{(dfmp)3MnIIMnII}MnIII(Me3Tacn)](ClO4) (5)

To an argon blanketed atmosphere 300 mg (1.5 mmol) H3dfmp was dissolved in

30 mL methanol and 0.4 mL (3 mmol) Triethylamine was added in it and it was stirred

for 10 min. Then 0.24 g (1 mmol) MnII(CH3COO)2 .4H2O was added and stirred. In

another round bottom flask 0.17 g (1 mmol) 1,4,7-trimethyl 1,4,7-triazacyclononane and

[MnIII3(µ3-O)(µ-CH3COO)6(H2O)3](CH3COO) (0.26 g) was dissolved in 20 mL methanol

and was stirred for20 minutes. This solution was added to the previous solution and then

it was refluxed for 20 minutes and the resulting solution turned brown black. After

cooling it was filtered off and 0.24 g (2 mmol) NaClO4 was added and after few minutes

brown solid precipitated out, was collected by filtration and air-dried. Suitable single

crystal for X-ray quality was grown from Acetonitrile-methanol (3:1) mixture. IR (KBr,

cm-1): 1607, 1567, 1542, 1460, 1438, 1322, 1229, 1144,1120,1107,1089 1006, 988,

705,624. ESI-MS (m/z): 567 (100 %) [M - 2(ClO4)]2+, 1135 (9 %) [M - ClO4]+.

Yield: 400 mg (37 %).

Formula Weight: 1308.38 C48H70N13O14ClMn4

EQUIPMENT AND EXPERIMENTAL WORK

Elemental Analysis:

%C %H %N %Mn

Calculated 44.06 5.39 13.91 16.8

Found 43.93 5.2 13.8 16.64

Infrared spectrum:

5001000150020002500300035004000

cm-1

Synthesis of [(Me3Tacn)MnIV{(dfmp)3MnIIMnII}MnIV(Me3Tacn)](ClO4)3 (6)

300 mg (1.5 mmol) H3dfmp was dissolved in 30 mL methanol and 0.4 mL (3

mmol) triethylamine was added in it and it was stirred for 10 min. Then 0.24 g (1 mmol)

MnII(CH3COO)2 .4H2O was added and stirred. In another round bottom flask 0.17 g (1

mmol) 1,4,7-trimethyl 1,4,7-triazacyclononane and [MnIII3(µ3-O)(µ-CH3COO)6(H2O)3](

CH3COO) (0.26 g) was dissolved in 20 mL methanol and was stirred for 20 minutes. This

solution was added to the previous solution and then it was refluxed for 20 minutes and

the resulting solution turned brown black. After cooling it was filtered off and 0.24 g (2

mmol) NaClO4 was added and after few minutes brown solid precipitated out, was

collected by filtration and air-dried. Suitable single crystal for X-ray quality was grown

from Acetonitrile-ethanol (3:1) IR (KBr, cm-1): 1607, 1567, 1542, 1460, 1438, 1322,

1229, 1144,1120,1107,1089 1006, 988, 705,624. ESI-MS (m/z): 567 (100 %) [M -

2(ClO4)]2+, 1135 (9 %) [M - ClO4]+.

Yield: 300 mg (29 %).

Molecular Weight: 1481.73 C46H67.5N12.5O22.5Cl3Mn4

CHAPTER 9

Elemental Analysis:

%C %H %N %Mn

Calculated 37.29 4.6 11.8 14.83

Found 37.4 4.73 11.7 14.62

Infrared spectrum:

5001000150020002500300035004000

cm-1

Synthesis of [(Me3Tacn)FeIII{(dfmp)3MnIIMnII}FeIII(Me3Tacn)](ClO4) (7)

300 mg (1.5 mmol) H3dfmp was dissolved in 30 mL methanol and 0.5 mL (4

mmol) triethylamine was added in it and it was stirred for 10 min. Then 0.24 g (1 mmol)

MnII(CH3COO)2 .4H2O was added and stirred, followed by L'FeCl3 (0.33 g, 1 mmol) and

then it was refluxed for 20 minutes under argon and the resulting solution turned brown

black. After cooling it was filtered off and 0.24 g (2 mmol) NaClO4 was added and after

few minutes red brown solid precipitated out and it was filtered through suction filtration

was washed with diethyl ether and then dried in air. Suitable single crystal for X-ray

quality was grown from Acetonitrile-dichloromethane (1:3). IR (KBr, cm-1): 1607, 1579,

1560, 1460, 1444, 1305, 1226, 1031, 1006, 988, 705. ESI-MS (m/z): 1137 (100 %) [M -

ClO4]+.

Yield: 390 mg (36 %).

Molecular Weight: 1236 C47.5H67N13O13Cl2Mn2Fe2

EQUIPMENT AND EXPERIMENTAL WORK

Elemental Analysis:

%C %H %N %Mn %Fe

Calculated 43.18 5.1 13.78 8.33 8.46

Found 43.22 4.95 13.57 8.21 8.39

Infrared Spectrum:

5001000150020002500300035004000

cm-1

Synthesis of [(Me3Tacn)CrIII{(dfmp)3MnIIMnII}CrIII[(Me3Tacn)](ClO4) (8)

300 mg (1.5 mmol) H3dfmp was dissolved in 30 mL Methanol and 0.5 mL(4

mmol) triethylamine was added in it and it was stirred for 10 min. Then 0.24 g (1 mmol)

MnII(CH3COO)2 .4H2O was added and stirred. To a suspension of 0.46 g (1 mmol) of

L'CrBr3 in 30 mL methanol was slowly added 0.63 g of AgClO4 (3 mmol) with stirring.

The suspension was refluxed under argon for 0.5 h; during this time a blue-violet solution

with a concomitant formation of AgBr resulted. Precipitated AgBr was filtered off, and

the clear blue-violet solution was charged to the previous methanolic solution and then it

was refluxed for 20 minutes under argon and the resulting solution turned brown black.

After cooling it was filtered off and green brown solid precipitated out and it was filtered

through suction filtration was washed with diethyl ether and then dried in air. Yield: 390

mg (36 %). IR (KBr, cm-1): 1607, 1579, 1560, 1460, 1444, 1305, 1226, 1031, 1006, 988,

705. ESI-MS (m/z): 1129 (100 %) [M - ClO4]+.

Yield: 390 mg (36 %).

Molecular Weight: 1236 C45H63N12O13ClMn2Cr2

CHAPTER 9

Elemental Analysis:

%C %H %N %Mn %Cr

Calculated 43.18 5.1 13.78 8.33 8.46

Found 40.13 4.95 13.60 8.71 8.59

Infrared Spectrum:

5001000150020002500300035004000

cm -1

Synthesis of [(Me3Tacn)2FeIII2L2CuII2(O..H..O)Cl](ClO4)2 (9)

[Cu(dapdoH2)2] (ClO4)2 (0.32 g, 0.5 mmol) was dissolved in 30 mL methanol. Then

L'FeCl3 (0.33 g, 1 mmol) was also added into the methanolic solution of [Cu(dapdoH2)2]

(ClO4)2, followed by Et3N (0.26 mL, 2 mmol). The resulting solution was refluxed for 30

minutes and then NaClO4 (0.36 g, 3 mmol) was added and then it was stirred for another

15 minutes. On cooling black microcrystalline solid precipitated out. It was then filtered

through suction filtration and washed with diethyl ether. Suitable quality X-ray crystal

was grown from CH3CN-C2H5OH mixture. IR (KBr, cm-1): 2906, 1593, 1502, 1545,

1459, 1444, 1297, 1163, 1077, 1006, 990, 781,623. ESI-MS (m/z): , 516(100 %) [M -

2ClO4]2+; 1131(5%) [M - ClO4]+

Yield: 290 mg (45%).

Formula Weight: 1295.18 C38H69N12O16Cl3Cu2Fe2

Elemental Analysis:

%C %H %N %Cu %Fe

Calculated 35.24 5.37 12.98 9.8 8.6

Found 34.9 5.3 12.98 9.7 8.46

EQUIPMENT AND EXPERIMENTAL WORK

Infrared spectrum:

5001000150020002500300035004000

cm-1

Synthesis of [(Me3Tacn)2CrIII2L2CuII2(OH)2Br2](ClO4)2 (10)

To a suspension of 0.46 g (1 mmol) of L'CrBr3 in 30 mL methanol was slowly added 0.46

g of AgClO4 (2 mmol) with stirring. The suspension was refluxed under argon for 0.5 h;

during this time a blue-violet solution with a concomitant formation of AgBr resulted.

Precipitated AgBr was filtered off, and the clear blue-violet solution was charged with a

solid sample (0.32 g, 0.5 mmol) of [Cu(dapdoH2)2] (ClO4)2 and 0.26 mL (2 mmol) Et3N.

The resulting green-brown solution was refluxed for 0.5 h, upon stirring at ambient

temperature, the mixture deposited green amorphous solid. These were filtered off and air

dried. Suitable quality X-ray crystal was grown from CH3CN-C2H5OH mixture. IR (KBr,

cm-1): 2916, 1595, 1560, 1461, 1295, 1164, 1090, 1004, 984, 794,624. ESI-MS (m/z): ,

579(100%)[(2 - 2ClO4+0.5H2O)/2]2+.

Yield: 230 mg (29%).

Molecular Weight: 1480.95 C42H72N15O14.5Br2Cl2Cu2Cr2

Elemental Analysis:

%C %H %N %Cu %Cr

Calculated 34.06 4.9 14.2 8.58 7.02

Found 33.8 4.87 14.1 8.41 7.09

CHAPTER 9

Infrared Spectrum:

5001000150020002500300035004000

cm-1

Synthesis of [MnII4(ppi)6](BF4)2 .2CH3CN . H2O (11)

The mononuclear precursor complex [MnIIL2] was prepared by reacting a solution of

Hppi (0.396 g, 2 mmol) in acetone (20 mL) with Mn(acac)2 (0.25 g, 1 mmol) in acetone

(30 mL). Upon addition of the ligand solution to the yellow slurry an immediate color

change to deep red observed. After stirring for 1 hr the red solid was isolated by filtration

and washed with acetone to yield 0.45 g [MnIIL2] complex.

[MnII4(ppi)6](BF4)2 was prepared by reacting [MnII(ppi)2] (0.45 g, 1 mmol) with

Mn(CH3COO)2 .4H2O (0.09 g, 0.33 mmol) in 3:1 ration in acetonitrile-methanol mixture

(30 mL, 1:1). It was stirred in air for 30 minutes and then NBu4BF4 (0.96 g, 3 mmol) was

added into the black solution. Red solid precipitated out and washed with diethyl ether

and dried in air. X-ray quality single crystal was grown by diffusing diethyl ether in

concentrated acetonitrile solution of the complex. IR(KBr, cm-1): 3053, 1585, 1479,

1457, 1298, 1280, 1146, 1083, 1061, 865, 750. ESI-MS (m/z): 701(100 %) [M -

2(BF4)]2+, 1489 (10 %) [M - BF4]+.

Yield: 220 mg (40 %).

Molecular Weight: 1676.78 C76H62B2F8Mn4N14O7

EQUIPMENT AND EXPERIMENTAL WORK

Elemental Analysis:

%C %H %N %Mn

Calculated 54.44 3.73 11.7 13.11

Found 54.37 3.62 11.6 13.15

Infrared Spectrum:

5001000150020002500300035004000

cm-1

Synthesis of [MnIII4(salox)4(salox H)4] 2.5 CH3OH (12)

Complex 12 was prepared by the addition of 1 mmol (0.198 g) of MnCl2 .4 H2O into a 40

mL methanol solution of 2 mmol (0.27 g) of salicylaldoxime in presence of triethylamine

(4 mmol, 0.52 mL) in argon blanketed atmosphere. Then the solution was refluxed for 30

minutes and then exposed in air and the solution turned to black. Brown black solid

precipitated out while cooling the solution. The X-ray quality single crystal was grown by

slow evaporation from 2:1 CH2Cl2-CH3OH solution of the complex. IR (KBr, cm-1):

3422, 2899, 1598, 1536, 1473, 1434, 1268, 1205, 1151, 1122, 1014, 909, 755, 666. ESI-

MS (m/z): 1032(100 %) [M - 2(salox H)]+, 1304 (10 %) [M ]

Yield: 180 mg (40 %).

Molecular Weight: 1384.86 C58.5H54Mn4N8O18.5

Elemental Analysis:

%C %H %N %Mn

Calculated 50.74 3.93 8.09 15.87

Found 50.57 3.84 8.04 15.93

Infrared Spectrum:

CHAPTER 9

5001000150020002500300035004000

cm-1

Synthesis of [(dapdo)2(dapdoH)4(µ-O)2(µ-OMe)2MnIII4MnII2](ClO4)2 (13)

To a solution of dapdoH2 (0.19 g, 1 mmol) in 30 mL methanol was added 0.26 g

[MnIII3(µ3-O)(µ-CH3COO)6(H2O)3](CH3COO), then 0.26 mL (2 mmol) Et3N. The

solution then turned brown, and it was then refluxed for 0.5 h whereupon a brown

microcrystalline solid was precipitated out. It was filtered and washed with diethyl ether

and air dried. Suitable quality of X-ray crystal was grown by diffusion of diethyl ether

into the DMF-CH3CN solution. IR (KBr, cm-1): 3425, 2805, 1597, 1542, 1375, 1141,

1121, 1052, 952, 811, 661, 624, 559. ESI-MS (m/z): 787(100 %) [M - 2(ClO4)]2+

solution then turned brown, and it was then refluxed for 0.5 h whereupon a brown

microcrystalline solid was precipitated out. It was filtered and washed with diethyl ether

and air dried. Suitable quality of X-ray crystal was grown by diffusion of diethyl ether

into the DMF-CH3CN solution. IR (KBr, cm-1): 3425, 2805, 1597, 1542, 1375, 1141,

1121, 1052, 952, 811, 661, 624, 559. ESI-MS (m/z): 787(100 %) [M - 2(ClO4)]2+

Yield: 150 mg (33 %) Yield: 150 mg (33 %)

Molecular Weight: 1922.03 C66H84Cl2N18Mn6O26

Elemental Analysis: Elemental Analysis:

%C %C %H %H %N %N %Mn %Mn

Calculated 40.73 4.35 12.96 16.94

Found 40.6 4.4 12.83 17.01

EQUIPMENT AND EXPERIMENTAL WORK

Infrared Spectrum:

cm-1

Synthesis of [(dapdo)2(dapdoH)4(µ-O)2(µ-OH)2MnIII4MnII2](ClO4)2 (14)

To a solution of dapdoH2 (0.19 g, 1 mmol) in 30 mL methanol was added 0.36 g

Mn(ClO4)2.6H2O, then 0.26 mL (2 mmol) Et3N. The solution then turned brown, and it

was then refluxed for 0.5 h whereupon a brown microcrystalline solid was precipitated

out. It was filtered and washed with diethyl ether and air dried. Suitable quality of X-ray

crystal was grown from concentrated CH3CN solution. IR (KBr, cm-1): 3425, 2805, 1598,

1542, 1375, 1141, 1121, 1080, 1052, 952, 812, 661, 624, 559. ESI-MS (m/z): 755(100 %)

[M - 2(ClO4)]2+

Yield: 100 mg (20 %).

Molecular Weight: 1992 C66H78Cl2N24Mn6O24

Elemental Analysis:

%C %H %N %Mn

Calculated 39.8 3.95 16.88 16.55

Found 39.94 3.84 16.85 16.42

CHAPTER 9

Infrared Spectrum:

5001000150020002500300035004000

cm-1

Synthesis of [L3(µ-O)(µ-OH) CuII6(H2O)6](BF4)3 (15)

To a light yellow solution of dioxime ligand (0.30 g; 1 mmol), Cu(CH3COO)2 .H2O

(0.40 g; 2 mmol) in distilled methanol (30 ml) was added with stirring, followed by

addition of 0.3 ml of Et3N. The resulting green solution was refluxed for 0.5 h and then

NBu4BF4 (0.64 g, 2 mmol) was added to procure dark green microcrystalline solid. X-ray

quality crystals were obtained from a mixture of CH3OH-CH3CN solution. IR (KBr, cm-

1): 3421, 1628, 1534, 1446, 1379, 1220, 1121, 1089, 687, 624 ESI-MS (m/z): 755(100 %)

[M - 3(BF4)]2+

Yield: 170 mg (25 %).

MolecularWeight:1683.85 C48H73B3N12Cu6O14F12

Elemental Analysis:

%C %H %N %Cu

Calculated 34.24 4.37 9.98 22.64

Found 34.38 4.4 9.91 22.55

EQUIPMENT AND EXPERIMENTAL WORK

Infrared Spectrum:

5001000150020002500300035004000

cm-1

Synthesis of [NiII9(PyA)10(µ3-OH)2(µ2-OH)2((µ2-OH2)2(H2O)6](ClO4)4 . 12H2O (16)

To a light green solution of NiCl2 .6H2O (0.47 g; 2 mmol) in water (25 ml), solid

pyridine-2-aldoxime(0.24g; 2 mmol) was added with stirring, followed by addition of

NaOH(0.10 g) to adjust the pH of the solution to 8. NaClO4 (0.36 g, 3 mmol) was added

as counter anion to isolate the light orange microcrystalline solid. X-ray quality crystals

were obtained by slow evaporation of the H2O-CH3OH (4:1) solution of the light orange

microcrystalline solid. IR (KBr, cm-1): 3441, 1604, 1540, 1476, 1223, 1141, 1120, 1088,

775, 683 626. ESI-MS (m/z): 781(100 %) [(PyA)5Ni3]+, 478(10 %) [(PyA)3Ni2]+,555(10

%) [(PyA)3Ni3(O)]+, 1058(10 %) [(PyA)6Ni4(ClO4)]+

Yield: 200 mg (25 %).

MolecularWeight: 2565.74 C60H94Cl4N20Ni9O50

Elemental Analysis:

%C %H %N %Ni

Calculated 28.9 3.7 10.92 20.59

Found 28.7 3.59 10.94 20.52

CHAPTER 9

Infrared Spectrum:

5001000150020002500300035004000

cm-1

Synthesis of [CuII9L14(µ3-OH)4(MeOH)2](ClO4)2 . 6MeOH (17)

To a light solution of the ligand (0.19 g; 0.5 mmol), Cu(ClO4)2 .6H2O (0.37 g; 1 mmol)

in distilled methanol (30 ml) was added with stirring, followed by addition of 0.5 ml of

Et3N. The resulting green solution was refluxed for 0.5 h and filter to procure dark green

microcrystalline solid. X-ray quality crystals were obtained from a mixture of CH2Cl2-

CH3OH solution. IR (KBr, cm-1): 3463, 1607, 1512, 1485, 1409, 1121, 1089, 704, 623.

ESI-MS (m/z): 1021(100%) [L2Cu4(OH)]+, 1523(50 %) [L3Cu6(OH)]+, 501(33 %)

[LCu2]+, 2075(15 %) [L4Cu8(OH)4]

Yield: 300 mg (50 %).

Molecular Weight: 2596.86 C100H128Cl2N8Cu9O32

Elemental Analysis:

%C %H %N %Cu

Calculated 46.25 4,97 4.31 22.02

Found 46.10 4.83 4.4 22.1

EQUIPMENT AND EXPERIMENTAL WORK

Infrared Spectrum:

5001000150020002500300035004000

cm-1

References:

(1) P. Chaudhuri, M. Winter, K. Wieghardt, S. Gehring, W. Haase, B. Nuber and J.

Weiss, Inorg. Chem., 1988, 27, 1564

(2) P. Chaudhuri, M. Winter, H. J. Kueppers, K. Wieghardt, B. Nuber and J. Weiss,

Inorg. Chem., 1987, 26, 3302

(3) C. W. Glynn and M. M. Turnbull, Transition. Met. Chem., 2002, 27, 822

(4) Y. Nishida and S. Kida, J. Chem. Soc., Dalton Trans., 1986, 2633

APPENDICES

APPENDICES:

(1) Crystallographic Data

(2) Magnetochemical Data

(3) Curriculum Vitae

(1) Crystallographic Data

Crystal data and structure refinement for 1, 2 and 3

1 2 3

Empirical formula C36H32N12O11ClMnNi2C36H30N12O10ClCrNi2C38H34N13O10ClNi3

Formula weight 1016.55 999.59 1044.36

Temperature (K) 100(2) 100(2) 100(2)

Wavelength (Å) 0.71073 0.71073 0.71073

Crystal system Rhombohedral Trigonal Monoclinic

Space group R-3 R-3 P2(1)/n

Unit cell dimensions a = 13.7375(4) Å

b = 13.7375(4) Å

c = 21.5674(6) Å

α = 90 deg.

β = 90deg.

γ = 120 deg.

a = 13.6398(3) Å

b = 13.6398(3) Å

c = 21.5949(5) Å

α = 90 deg.

β = 90deg.

γ = 120 deg.

a = 11.1498(3) Å

b = 15.8194 (3) Å

c = 23.9548(6) Å

α = 90deg

β = 102.13(1) deg.

γ = 90deg.

Volume (Å3);Z 3524.87(18); 3 3479.35(13); 3 4130.9(2); 4

Density (cal.) (Mg/m3) 1.437 1.425 1.679

Absorp. coeff. (mm-1) 1.180 1.155 1.494

F(000)

Crystal size

1554

0.12 x 0.09 x 0.09 mm

1521

0.10 x 0.10 x 0.10 mm

1510

0.15 x 0.12 x 0.08 mm

θ range for data collection 3.55 to 28.31 deg. 4.12 to 31.04 deg. 3.09 to 31.03 deg.

Index ranges -18<=h<=18,

-18<=k<=18,

-28<=l<=28

-19<=h<=19,

-19<=k<=19,

-31<=l<=31

-16<=h<=16,

-22<=k<=22,

-34<=l<=34

Reflections collected 20351 2998 106567

Independent reflections 1941[R(int) = 0.0355)] 2467[R(int) = 0.0306)] 13148[R(int) = 0.0525)]

Absorption correction not corrected not corrected not corrected

Data / restraints / parameters 1941 / 21 / 127 2467 / 19 / 132 13132 / 1 / 593

Goodness-of-fit on F2 1.091 1.110 1.052

Final R indices

[I>2σ(I)]

R1 = 0.0325,

wR2 = 0.0944

R1 = 0.0349,

wR2 = 0.1088

R1 = 0.0355,

wR2 = 0.0726

R indices (all data) R1 = 0.0359,

wR2 = 0.0970

R1 = 0.0383,

wR2 = 0.1118

R1 = 0.0461,

wR2 = 0.0821

APPENDICES

Crystal data and structure refinement for 4, 5, 6 and 7

4 5 6 7

Empirical formula C37H49B2N7O10Mn2

C48H70ClN13O14Mn4C46H67.5Cl3N12.5O22.Mn4C47.5H67Cl2N13O13Mn2Fe2

Formula weight 883.33 1308.38 1481.73 1320.62

Temperature 100(2) K 100(2) K 100(2) K 100(2) K

Wavelength (MoKα) 0.71073 Å 0.71073 Å 0.71073 0.71073 Å

Crystal System Trigonal Monoclinic Triclinic Monoclinic

Space group P3121 P2(1)/c P-1 P2(1)/c

Unit cell dimensions a = 11.269(3) Å a = 16.485(2) Å a = 17.026(4) Å a = 14.411(4) Å

b = 11.269(3) Å b = 14.494(2) Å b = 18.267(4) Å b = 16.699(6) Å

c = 27.733(7) Å c = 24.365(3) Å c = 23.598(6) Å c = 25.02(8) Å

α = 90oα = 90oα = 101.44 (1)oα = 90o

β = 90oβ = 90.26(2)oβ = 108.57(1)oβ = 104.82(4)o

γ = 120oγ = 90oγ = 105.65(1)oγ = 90o

Volume (Å3); Z 3050.4(14); 3 5821.6(13); 4 6366.2; 4 5820.8(3); 4

Density (calc.) Mg/m31.443 1.493 1.546 1.507

Absorp. coeff. (mm-1) 0.686 1.043 0.984 1.075

F(000) 1380 2712 3048 2732

Crystal size (mm) 0.18 x 0.17 x 0.12 0.11 x 0.06 x 0.02 0.12 x 0.10 x 0.05 0.06 x 0.05 x 0.05

θ range for data collect. 3.04 to 30.48o3.18 to 22.50o2.92 to 27.5o2.08 to 30.55o

Reflections collected 63879 49350 114428 65527

Independent reflect. 6165

[R(int.) = 0.424]

7587

[R(int.) = 0.1044]

29183

[R(int.) = 0.0721]

17765

[R(int.) = 0.0631]

Absorpt. correction not measured not measured Gaussian,

face indexed

not measured

Data/restraints/param. 6157 / 9 / 281 7587 / 8 / 711 29183 / 906 / 1655 17632 / 7 / 760

Goodness-of-fit on F2

Final R indices

[I>2σ(I)

R indices (all data)

1.107

R1 = 0.0379

wR2 = 0.0980

R1 = 0.0420

wR2 = 0.1130

1.216

R1 =0.1044

wR2 = 0.1595

R1 = 0.1430

wR2 = 0.1737

1.029

R1 = 0.0756

wR2 = 0.1929

R1 = 0.1075

wR2 = 0.2143

1.012

R1 = 0.0527

wR2 = 0.1263

R1 = 0.0856

wR2 = 0.1494

APPENDICES

9 10

Empirical formula C38H69N12O16Cl3Cu2Fe2C42H72N15O14.5Br2Cl2Cr2Cu2

Formula weight 1295.18 1480.95

Temperature (K) 100(2) 100(2)

Wavelength (Å) 0.71073 0.71073

Crystal system Monoclinic Triclinic

Space group C2/c P-1

Unit cell dimensions a = 27.449(6) Å

b = 8.976(2) Å

c = 24.038(6) Å

α = 90 deg.

β = 119.883(6) deg.

γ = 90 deg.

a = 14.607(4) Å

b = 15.153 (4) Å

c = 15.186(5) Å

α = 88.13(4) deg.

β = 86.56(4) deg.

γ = 62.57(4) deg.

Volume (Å3);Z 5135.2(2); 4 2798.00(15); 2

Density (cal.) (Mg/m3) 1.675 1.652

Absorp. coeff. (mm-1) 1.605 2.563

F(000)

Crystal size

2324 1510

θ range for data collection 3.91 to 31.02 deg. 2.97 to 31.06 deg.

Index ranges -39<=h<=39,

-13<=k<=13,

-34<=l<=34

-21<=h<=21,

-21<=k<=21,

-21<=l<=21

Reflections collected 48703 85582

Independent reflections 8163[R(int) = 0.0589)] 18949[R(int) = 0.0396)]

Absorption correction not corrected Gaussian, face indexed

Data / restraints / parameters 8163 / 0 / 339 18883 / 101 / 772

Goodness-of-fit on F2 1.025 1.019

Final R indices

[I>2σ(I)]

R1 = 0.0348, wR2 = 0.0709 R1 = 0.0345, wR2 = 0.0806

R indices (all data) R1 = 0.0477, wR2 = 0.0755 R1 = 0.0452, wR2 = 0.1026

Crystal data and structure refinement for 9, and 10

APPENDICES

Crystal data and structure refinement for 11 and 12

11 12

Empirical formula C76 H62 B2 Mn4 N14 O7F8

C58.5 H54 Mn4 N8 O18.5

Formula weight 1676.78 1384.86

Temperature (K) 100(2) 100(2)

Wavelength (Å) 0.71073 0.71073

Crystal system Tetragonal Triclinic

Space group I41/a No. 88 P-1

Unit cell dimensions a = 17.0154(9) Å

b = 17.0154(9) Å

c = 53.619(4) Å

α =90 deg.

β = 90deg.

γ = 90deg.

a = 12.3968(9) Å

b = 14.715(2)Å

c = 16.716(2)Å

α = 84.15(1) deg.

β = 84.11(1)deg.

γ = 89.48(1) deg.

Volume (Å3);Z 15524.0(16); 8 3017.4(6); 2

Density (calculated) (Mg/m3) 1.435 1.524

Absorption coefficient (mm-1) 0.717 0.898

F(000) 6832 1418

Crystal size (mm) 0.23 x 0.17 x 0.13 0.04 x 0.01 x 0.01

θ range for data collection 2.24 to 26.35 deg. 2.93 to 22.50

Index ranges -21<=h<=20,

-21<=k<=20,

-66<=l<=66

-13<=h<=12,

-15<=k<=15,

-17<=l<=17

Reflections collected 53622 21974

Independent reflections 7932 [R(int) = 0.0338] 7884 [R(int) = 0.0931]

Absorption correction Gaussian, face-indexed Not measured

Data / restraints / parameters 7843 / 0 / 570 7884 / 12 / 837

Goodness-of-fit on F2 1.028 1.032

Final R indices

[I>2σ(I)]

R1 = 0.0353,

wR2 = 0.930

R1 = 0.0600,

wR2 = 0.1137

R indices (all data) R1 = 0.0571,

wR2 = 0.1742

R1 = 0.1215,

wR2 = 0.1365

APPENDICES

Crystal data and structure refinement for 13, 14 and 15

13 14 15

Empirical formula C66 H84 Cl2 Mn6 N18 O26

C66 H78Cl2 Mn6 N24 O24 C48 H73B3Cu6 F12 N12 O14

Formula weight 1922.03 1992.06 1683.85

Temperature (K) 100(2) 100(2) 100(2)

Wavelength (Å) 0.71073 0.71073 0.71073

Crystal system Triclinic Triclinic Cubic

Space group P-1 P-1 Pa-3, No. 205

Unit cell dimensions a = 10.636(2) Å

b = 13.270(3) Å

c = 15.515(3) Å

α =65.48(2) deg.

β = 82.81(2) deg.

γ = 84.62(2) deg.

a = 10.9213(9) Å

b = 13.5592(12)Å

c = 15.444(2)Å

α = 101.75(1) deg.

β = 107.72(1)deg.

γ = 98.08(1) deg.

a = 23.8313(9) Å

b = 23.8313(9) Å

c = 23.8313(9) Å

α = 90 deg.

β = 90deg.

γ= 90 deg.

Volume (Å3);Z 1974.5(7); 1 2081.9(4); 1 13534.5(9); 8

Density (calculated) (Mg/m3) 1.616 1.589 1.653

Absorption coefficient (mm-1) 1.087 1.034 1.951

F(000) 986 1018 6832

Crystal size (mm) 0.04 x 0.03 x 0.03 0.06 x 0.04 x 0.04 0.36 x 0.32 x 0.22

θ range for data collection 2.3 to 25.00 deg. 3.43 to 27.50 3.01 to 27.50 deg.

Index ranges -13<=h<=13,

-16<=k<=16,

-19<=l<=19

-14<=h<=15,

-19<=k<=19,

-20<=l<=20

-31<=h<=30,

-31<=k<=31,

-31<=l<=31

Reflections collected 25689 23688 118922

Independent reflections 6943 [R(int) = 0.0824] 9500 [R(int) = 0.0857] 5319 [R(int) = 0.0570]

Absorption correction Not measured Not measured Gaussian, face-indexed

Data / restraints / parameters 6879 / 95 / 570 9385 / 3 / 568 5319 / 95 / 314

Goodness-of-fit on F2 1.050 1.010 1.057

Final R indices

[I>2σ(I)]

R1 = 0.0598,

wR2 = 0.1180

R1 = 0.0543,

wR2 = 0.0916

R1 = 0.0427,

wR2 = 0.1139

R indices (all data) R1 = 0.1108,

wR2 = 0.1397

R1 = 0.1180,

wR2 = 0.1139

R1 = 0.0531,

wR2 = 0.1246

APPENDICES

Crystal data and structure refinement for 16 and 17

16 17

Empirical formula C60H94Cl4N20Ni9O50 C100H128N8O32Cl2Cu9

Formula weight 2565.74 2596.86

Temperature (K) 100(2) 100(2)

Wavelength (Å) 0.71073 0.71073

Crystal system Monoclinic Triclinic

Space group C2/c , No. 15 P-1

Unit cell dimensions a = 24.704(2) Å

b = 31.015(3) Å

c = 26.032(2) Å

α = 90 deg.

β = 100.13(2) deg.

γ = 90 deg.

a = 13.0636(4) Å

b = 15.2420 (6) Å

c = 16.0330(6) Å

α = 107.71(1) deg.

β = 112.03(1) deg.

γ = 101.11(1) deg.

Volume (Å3);Z 19635.3(2); 8 2643.47(15); 1

Density (cal.) (Mg/m3) 1.736 1.631

Absorp. coeff. (mm-1) 1.899 1.907

F(000)

Crystal size

10512

0.28x0.06x0.06 mm

1335

0.16x0.15x0.10 mm

θ range for data collection 2.97 to 22.50 deg. 2.99 to 31.10 deg.

Index ranges -26<=h<=26,

-33<=k<=33,

-28<=l<=28

-18<=h<=18,

-22<=k<=22,

-23<=l<=21

Reflections collected 103240 66247

Independent reflections 12807[R(int) = 0.0984)] 16905[R(int) = 0.0513)]

Absorption correction Gaussian, face indexed Gaussian, face indexed

Data / restraints / parameters 12807 /93 0 / 1467 16905 / 1 / 702

Goodness-of-fit on F2 1.111 1.040

Final R indices

[I>2σ(I)]

R1 = 0.0717, wR2 = 0.1593 R1 = 0.0446, wR2 = 0.0989

R indices (all data) R1 = 0.0926, wR2 = 0.1703 R1 = 0.0616, wR2 = 0.1026

APPENDICES

(2) Magnetochemical Data

Complex NiIIMnIIINiII (1)

MW = 837.0 g/mol, χdia = -425.0 x 10-6 cm3 mol-1

m = 32.57 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.951 0.33602 0.01984 1.6393 0.39835

2 5.116 0.83956 0.33326 2.59122 1.63257

3 10.144 1.37563 0.89542 3.31688 2.67604

4 15.046 1.79121 1.44128 3.78488 3.39511

5 20.003 2.14802 1.92967 4.14475 3.92845

6 30.002 2.70188 2.66048 4.6485 4.61274

7 39.999 3.09273 3.13414 4.97337 5.00655

8 50.006 3.38002 3.45382 5.19923 5.25568

9 60.043 3.59354 3.68111 5.36094 5.42586

10 70.058 3.7587 3.84908 5.48275 5.54827

11 80.067 3.8952 3.978 5.58141 5.64042

12 90.09 4.00346 4.08005 5.65845 5.71231

13 100.1 4.09563 4.16253 5.72321 5.76976

14 110.15 4.1709 4.23085 5.77556 5.81692

15 120.12 4.2364 4.28772 5.82074 5.85589

16 130.17 4.28919 4.33647 5.85689 5.88908

17 140.18 4.34007 4.37826 5.89153 5.91739

18 150.19 4.38152 4.41461 5.91959 5.9419

19 160.19 4.42087 4.44647 5.94611 5.96331

20 170.22 4.45514 4.47473 5.96912 5.98223

21 180.22 4.48471 4.49983 5.98889 5.99898

22 190.22 4.51229 4.52233 6.00728 6.01396

23 200.24 4.53428 4.54265 6.0219 6.02746

24 210.16 4.55519 4.56089 6.03577 6.03954

25 220.26 4.57663 4.57778 6.04996 6.05072

26 230.26 4.59272 4.59306 6.06058 6.06081

27 240.26 4.6115 4.60709 6.07296 6.07006

28 250.26 4.62828 4.62 6.084 6.07856

29 260.27 4.64631 4.63194 6.09584 6.08641

30 270.26 4.66375 4.64299 6.10727 6.09366

31 280.27 4.67325 4.65327 6.11349 6.1004

32 290.27 4.69206 4.66284 6.12578 6.10667

APPENDICES

Complex NiIICrIIINiII (2)

MW = 995 g/mol, χdia = -420 x 10-6 cm3 mol-1

m = 63.45 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.912 2.93923 3.39597 4.84837 5.21148

2 5.089 3.99861 4.11896 5.65502 5.73949

3 9.999 4.11023 4.09724 5.7334 5.72434

4 14.959 4.05373 4.02934 5.69386 5.67671

5 20.004 3.99144 3.98056 5.64994 5.64224

6 29.999 3.9079 3.92252 5.59051 5.60095

7 39.996 3.86411 3.88978 5.5591 5.57753

8 50.009 3.83246 3.86892 5.53628 5.56255

9 60.047 3.82229 3.8545 5.52893 5.55218

10 70.052 3.81195 3.844 5.52145 5.54461

11 80.068 3.81108 3.83599 5.52082 5.53883

12 90.105 3.80872 3.82967 5.51911 5.53427

13 100.12 3.81586 3.82458 5.52428 5.53059

14 110.11 3.81745 3.82039 5.52543 5.52756

15 120.12 3.82319 3.81687 5.52958 5.52501

16 130.11 3.82085 3.81389 5.52789 5.52285

17 140.18 3.82048 3.81129 5.52762 5.52097

18 150.19 3.80833 3.80905 5.51883 5.51935

19 160.21 3.79812 3.80708 5.51142 5.51792

20 170.21 3.79525 3.80535 5.50934 5.51667

21 180.22 3.79464 3.80379 5.5089 5.51554

22 190.23 3.7969 3.8024 5.51054 5.51453

23 200.24 3.79574 3.80115 5.5097 5.51362

24 210.24 3.79607 3.80001 5.50994 5.51279

25 220.27 3.79687 3.79898 5.51052 5.51205

26 230.26 3.79938 3.79803 5.51234 5.51136

27 240.25 3.80528 3.79716 5.51662 5.51073

28 250.26 3.81294 3.79636 5.52217 5.51015

29 260.16 3.81381 3.79563 5.5228 5.50962

30 270.25 3.82078 3.79494 5.52784 5.50912

31 280.25 3.8247 3.7943 5.53067 5.50865

32 290.25 3.83429 3.79371 5.5376 5.50822

APPENDICES

Complex NiII3 (3)

MW = 1044 g/mol, χdia = -430 x 10-6 cm3 mol-1

m = 54.25 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.96 0.80356 0.98983 2.53507 2.81358

2 5.11 0.97353 1.02925 2.79032 2.86906

3 9.99 1.0331 1.00545 2.87442 2.8357

4 15.02 1.12205 1.07778 2.99561 2.93592

5 20.01 1.2452 1.21 3.15572 3.1108

6 30.00 1.51542 1.50578 3.48134 3.47025

7 40.01 1.75747 1.76298 3.74907 3.75494

8 50.01 1.9538 1.96718 3.95293 3.96645

9 60.02 2.10845 2.12762 4.1064 4.12502

10 70.06 2.23365 2.25491 4.22656 4.24663

11 80.07 2.33672 2.35677 4.32298 4.34148

12 90.09 2.42075 2.4402 4.40002 4.41766

13 100.12 2.49276 2.50933 4.46498 4.4798

14 110.13 2.55149 2.56741 4.51727 4.53134

15 120.14 2.60448 2.61687 4.56394 4.57478

16 130.16 2.64714 2.6595 4.60117 4.61189

17 140.18 2.68774 2.69656 4.63632 4.64392

18 150.14 2.72092 2.72887 4.66485 4.67166

19 160.2 2.75367 2.75771 4.69284 4.69628

20 170.21 2.78267 2.78323 4.71748 4.71796

21 180.22 2.80758 2.80609 4.73855 4.73729

22 190.23 2.83175 2.82667 4.7589 4.75463

23 200.24 2.85184 2.84529 4.77575 4.77027

24 210.24 2.87148 2.86221 4.79217 4.78443

25 220.25 2.88915 2.87767 4.80689 4.79733

26 230.26 2.90473 2.89184 4.81984 4.80913

27 240.25 2.92129 2.90484 4.83356 4.81993

28 250.25 2.93752 2.91686 4.84696 4.82989

29 260.27 2.95348 2.92801 4.86011 4.83911

30 270.25 2.96902 2.93832 4.87288 4.84762

31 280.26 2.98144 2.94794 4.88306 4.85555

32 290.24 2.99747 2.95689 4.89617 4.86292

APPENDICES

Complex MnIIMnII (4)

MW = 837.0 g/mol, χdia = -425.0 x 10-6 cm3 mol-1

m = 32.57 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.948 0.0677 0.01015 0.73581 0.01018

2 5.119 0.16488 0.02578 1.14832 0.45402

3 9.996 0.35264 0.21482 1.67936 1.31074

4 15.039 0.55982 0.43311 2.11595 1.86114

5 20.005 0.75228 0.63946 2.45284 2.26144

6 30.001 1.1297 1.04851 3.00581 2.89578

7 39.998 1.50433 1.4553 3.46857 3.41158

8 50.008 1.87591 1.86014 3.87334 3.85702

9 60.045 2.24432 2.2595 4.23664 4.25095

10 70.05 2.60378 2.64487 4.56333 4.59919

11 80.075 2.94663 3.0123 4.85447 4.90827

12 90.093 3.27157 3.35655 5.11514 5.18115

13 100.14 3.57341 3.6766 5.3459 5.42254

14 110.13 3.85239 3.96939 5.55066 5.63432

15 120.13 4.1087 4.2378 5.73234 5.8217

16 130.17 4.34608 4.4839 5.8956 5.98835

17 140.18 4.56144 4.70773 6.03991 6.136

18 150.19 4.76215 4.91199 6.17136 6.2677

19 160.21 4.94278 5.09873 6.28731 6.38573

20 170.22 5.11166 5.26937 6.39382 6.4917

21 180.22 5.26377 5.42559 6.48825 6.58723

22 190.24 5.40441 5.56934 6.57436 6.67392

23 200.24 5.53466 5.70136 6.65311 6.75256

24 210.25 5.65088 5.82325 6.7226 6.82436

25 220.25 5.76244 5.93581 6.78864 6.89

26 230.25 5.86172 6.0401 6.84687 6.95027

27 240.26 5.95191 6.13702 6.89934 7.00581

28 250.17 6.03728 6.22633 6.94864 7.0566

29 260.26 6.12128 6.31111 6.99682 7.10448

30 270.26 6.20203 6.38957 7.04282 7.1485

31 280.26 6.28144 6.46301 7.08776 7.18947

32 290.23 6.35298 6.53167 7.12801 7.22756

APPENDICES

Complex MnIIIMnIIMnIIMnIII (5)

MW = 1234 g/mol, χdia = -630.0 x 10-6 cm3 mol-1

m = 34.79 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.951 0.79064 0.53854 2.5146 2.07533

2 5.072 1.89519 1.48217 3.89319 3.44293

3 9.997 2.94776 2.69293 4.85541 4.64079

4 15.028 3.82114 3.69206 5.5281 5.43393

5 20.004 4.55633 4.50875 6.03652 6.00492

6 30 5.73805 5.74341 6.77426 6.77742

7 39.999 6.65335 6.61325 7.29457 7.27255

8 50.009 7.38764 7.27651 7.68656 7.62853

9 60.022 7.9832 7.81704 7.99039 7.9068

10 70.058 8.47748 8.27621 8.23404 8.1357

11 80.08 8.88361 8.67223 8.42896 8.32808

12 90.088 9.2187 9.01671 8.58646 8.49187

13 100.11 9.4894 9.3184 8.71162 8.63277

14 110.13 9.72049 9.58288 8.81705 8.75442

15 120.17 9.91151 9.81584 8.90327 8.86019

16 130.16 10.0726 10.0203 8.97533 8.95199

17 140.18 10.2081 10.2017 9.03549 9.03266

18 150.18 10.3344 10.3625 9.09122 9.10357

19 160.13 10.4319 10.5052 9.134 9.16604

20 170.2 10.5331 10.6344 9.1782 9.22223

21 180.23 10.6111 10.75 9.2121 9.27222

22 190.23 10.6783 10.853 9.24124 9.31688

23 200.24 10.7431 10.9479 9.26924 9.35718

24 210.24 10.7904 11.0332 9.28962 9.39356

25 220.26 10.8469 11.1111 9.31391 9.42666

26 230.25 10.893 11.1821 9.33369 9.45673

27 240.28 10.9354 11.2475 9.35183 9.48435

28 250.27 10.98 11.3073 9.37088 9.50953

29 260.27 11.007 11.3625 9.3824 9.53271

30 270.26 11.0346 11.4136 9.39415 9.55412

31 280.25 11.0707 11.4608 9.40951 9.57386

32 290.26 11.0718 11.5049 9.40998 9.59226

APPENDICES

Complex MnIVMnIIMnIIMnIV (6)

MW = 1433 g/mol, χdia = -700.0 x 10-6 cm3 mol-1

m = 33.63 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.916 1.21603 1.75514 3.11854 3.74658

2 5.11 2.91624 3.31404 4.82938 5.14823

3 9.994 3.99506 4.62802 5.65251 6.08383

4 15.014 5.00867 5.45928 6.32908 6.60765

5 20.005 5.85464 6.11183 6.84273 6.99141

6 30.001 7.18731 7.23633 7.58163 7.60744

7 40 8.21043 8.21261 8.10331 8.10438

8 50.013 9.02793 9.04005 8.49715 8.50286

9 60.031 9.69277 9.72286 8.80447 8.81813

10 70.038 10.2385 10.2805 9.04894 9.06748

11 80.069 10.694 10.7386 9.24804 9.2673

12 90.089 11.0777 11.1163 9.41248 9.42887

13 100.13 11.39 11.432 9.54424 9.56182

14 110.13 11.6566 11.6969 9.65529 9.67197

15 120.14 11.8802 11.9228 9.74746 9.76492

16 130.16 12.0724 12.1171 9.82599 9.84416

17 140.17 12.234 12.2856 9.89153 9.91237

18 150.19 12.3887 12.433 9.95388 9.97166

19 160.14 12.4916 12.5621 9.99513 10.0233

20 170.21 12.6331 12.6779 10.05158 10.06939

21 180.23 12.7325 12.7808 10.09105 10.11017

22 190.23 12.8205 12.8729 10.12586 10.14653

23 200.23 12.9041 12.956 10.15882 10.17923

24 210.24 12.9741 13.0314 10.18634 10.20881

25 220.24 13.0507 13.1 10.21636 10.23564

26 230.25 13.1102 13.1628 10.23963 10.26015

27 240.24 13.159 13.2203 10.25867 10.28253

28 250.26 13.2152 13.2734 10.28055 10.30316

29 260.27 13.2625 13.3223 10.29893 10.32212

30 270.26 13.3201 13.3676 10.32127 10.33966

31 280.26 13.3867 13.4096 10.34704 10.35589

32 290.25 13.436 13.4488 10.36608 10.37101

APPENDICES

Complex FeIIIMnIIMnIIFeIII (7)

MW = 1236 g/mol, χdia = -592.0 x 10-6 cm3 mol-1

m = 22.75 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.959 1.32852 0.79258 3.25959 2.5177

2 5.01 2.77139 2.03779 4.70791 4.037

3 9.996 4.22679 3.66287 5.81413 5.4124

4 14.994 5.31265 4.95719 6.51831 6.29647

5 20.005 6.17474 5.97047 7.0273 6.91009

6 30 7.45581 7.35645 7.72195 7.67032

7 40.002 8.39672 8.26324 8.19472 8.12933

8 50 9.14143 8.94522 8.5504 8.45814

9 60.038 9.76769 9.51563 8.83843 8.72365

10 70.056 10.2858 10.0168 9.06982 8.95043

11 80.089 10.7361 10.4698 9.26622 9.15058

12 90.1 11.1224 10.8813 9.43145 9.32867

13 100.12 11.4475 11.2574 9.5683 9.48852

14 110.13 11.7448 11.6005 9.69175 9.63203

15 120.14 11.9972 11.9139 9.79534 9.76127

16 130.17 12.2252 12.2007 9.88798 9.87806

17 140.19 12.4247 12.4626 9.96833 9.98352

18 150.19 12.6103 12.7019 10.04251 10.07891

19 160.2 12.7793 12.9215 10.10958 10.16567

20 170.22 12.9289 13.1233 10.16858 10.24474

21 180.23 13.0787 13.3089 10.22732 10.31693

22 190.24 13.2042 13.4801 10.27627 10.38307

23 200.24 13.3299 13.6381 10.32507 10.44375

24 210.24 13.4435 13.7844 10.36897 10.49961

25 220.26 13.5514 13.9206 10.4105 10.55136

26 230.25 13.6678 14.0468 10.45511 10.59908

27 240.25 13.7637 14.1645 10.49173 10.64339

28 250.26 13.8558 14.2746 10.52677 10.68468

29 260.27 13.9436 14.3776 10.56007 10.72316

30 270.25 14.0124 14.4738 10.58609 10.75897

31 280.17 14.1152 14.5637 10.62485 10.79233

32 290.26 14.2252 14.6496 10.66617 10.82411

APPENDICES

Complex CrIIIMnIIMnIICrIII (8)

MW = 1228 g/mol, χdia = -625.0 x 10-6 cm3 mol-1

m = 39.54 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.952 0.59263 0.25479 2.17707 1.42748

2 5.138 1.36712 0.8418 3.30661 2.59469

3 9.969 1.81119 1.55265 3.80594 3.52384

4 15.007 2.18216 2.14702 4.17756 4.14379

5 20.005 2.53284 2.61344 4.50073 4.57178

6 30 3.19519 3.297 5.05508 5.13498

7 39.998 3.80295 3.8081 5.51493 5.51866

8 50.01 4.33953 4.24381 5.89116 5.82582

9 60.034 4.82463 4.64128 6.21171 6.09254

10 70.055 5.25082 5.01295 6.48027 6.33178

11 80.069 5.62698 5.36218 6.70837 6.54862

12 90.093 5.96075 5.68979 6.90446 6.74571

13 100.13 6.24829 5.99551 7.06903 6.92456

14 110.13 6.5057 6.27796 7.21317 7.0858

15 120.11 6.72787 6.53843 7.33531 7.2313

16 130.16 6.93391 6.78015 7.44678 7.36375

17 140.18 7.11205 7.00194 7.54183 7.48322

18 150.19 7.27804 7.2058 7.62933 7.59138

19 160.21 7.42578 7.39365 7.70638 7.68969

20 170.21 7.5584 7.56638 7.77489 7.77899

21 180.22 7.6811 7.72591 7.83774 7.86057

22 190.23 7.78637 7.87331 7.89127 7.9352

23 200.23 7.89224 8.0096 7.94474 8.00359

24 210.23 7.98217 8.13599 7.98987 8.06649

25 220.26 8.06887 8.25374 8.03315 8.12465

26 230.26 8.15133 8.36299 8.07409 8.17825

27 240.25 8.22445 8.46477 8.11022 8.22786

28 250.24 8.296 8.55985 8.14543 8.27394

29 260.27 8.36422 8.64917 8.17885 8.317

30 270.26 8.41954 8.73256 8.20585 8.357

31 280.26 8.48277 8.81094 8.23661 8.39442

32 290.15 8.5273 8.88388 8.2582 8.42909

APPENDICES

Complex FeIII2CuII2 (9)

MW = 1295.0 g/mol, χdia = -620.0 x 10-6 cm3 mol-1

m = 18.61 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.947 6.15347 6.18609 7.01519 7.03376

2 5.025 8.40454 8.49109 8.19854 8.24064

3 10.058 8.39965 8.34069 8.19615 8.16734

4 15.031 7.95016 7.90105 7.97384 7.94917

5 20.003 7.62678 7.58346 7.80998 7.78777

6 30 7.21982 7.19946 7.59876 7.58804

7 39.997 6.99787 6.98533 7.48105 7.47434

8 50.009 6.86339 6.85034 7.40881 7.40177

9 60.01 6.76545 6.75804 7.35576 7.35173

10 70.055 6.6945 6.69076 7.31709 7.31505

11 80.075 6.64977 6.63989 7.29261 7.28719

12 90.094 6.61113 6.60007 7.27139 7.2653

13 100.11 6.57834 6.56814 7.25333 7.24771

14 110.1 6.55335 6.5422 7.23954 7.23338

15 120.15 6.53128 6.52081 7.22734 7.22155

16 130.16 6.51287 6.5034 7.21715 7.2119

17 140.18 6.49725 6.48937 7.20849 7.20412

18 150.19 6.48503 6.47844 7.20171 7.19805

19 160.2 6.48535 6.47042 7.20188 7.19359

20 170.22 6.46962 6.46519 7.19314 7.19068

21 180.21 6.49148 6.46268 7.20529 7.18929

22 190.23 6.46212 6.46283 7.18897 7.18937

23 200.24 6.46348 6.46557 7.18973 7.19089

24 210.24 6.46667 6.47083 7.1915 7.19382

25 220.26 6.4667 6.47854 7.19152 7.1981

26 230.25 6.47453 6.48859 7.19587 7.20368

27 240.15 6.4784 6.50074 7.19802 7.21042

28 250.26 6.48892 6.51531 7.20387 7.2185

29 260.27 6.50329 6.53173 7.21184 7.22759

30 270.25 6.51218 6.54996 7.21677 7.23767

31 280.26 6.52818 6.56996 7.22563 7.24871

32 290.26 6.55049 6.59152 7.23796 7.26059

APPENDICES

Complex CrIII2CuII2 (10)

MW = 1348 g/mol, χdia = -610.0 x 10-6 cm3 mol-1

m = 37.89 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.949 1.25667 2.4444 3.17022 4.42146

2 5.091 2.56664 2.81681 4.53066 4.74633

3 10.153 2.85421 2.87389 4.77774 4.79418

4 15.046 2.85834 2.86638 4.78119 4.78791

5 20.005 2.82607 2.83215 4.75413 4.75924

6 30 2.72395 2.72977 4.66744 4.67243

7 40.001 2.63192 2.626 4.58792 4.58276

8 50.01 2.55155 2.53778 4.51733 4.50512

9 60.041 2.48523 2.46667 4.45823 4.44155

10 70.055 2.43778 2.41147 4.41547 4.39158

11 80.049 2.40619 2.37065 4.38676 4.35425

12 90.107 2.38338 2.34285 4.36592 4.32864

13 100.11 2.36909 2.32739 4.35281 4.31434

14 110.13 2.36202 2.323 4.34631 4.31027

15 120.15 2.36645 2.32848 4.35039 4.31535

16 130.16 2.37514 2.34248 4.35837 4.3283

17 140.18 2.39356 2.36369 4.37524 4.34785

18 150.19 2.41592 2.39075 4.39563 4.37267

19 160.21 2.44451 2.42249 4.42156 4.4016

20 170.21 2.48274 2.45773 4.456 4.4335

21 180.22 2.5103 2.49561 4.48066 4.46753

22 190.16 2.54717 2.53501 4.51345 4.50266

23 200.25 2.58604 2.57615 4.54775 4.53905

24 210.23 2.62565 2.61743 4.58245 4.57527

25 220.25 2.6658 2.65901 4.61735 4.61147

26 230.25 2.70577 2.7003 4.65184 4.64714

27 240.26 2.74667 2.74115 4.68687 4.68216

28 250.26 2.78569 2.78127 4.72004 4.7163

29 260.27 2.82566 2.8206 4.75378 4.74952

30 270.26 2.86462 2.85889 4.78644 4.78165

31 280.27 2.89995 2.89622 4.81587 4.81277

32 290.24 2.93601 2.93234 4.84572 4.84269

APPENDICES

Complex MnII4 (11)

MW = 1576 g/mol, χdia = -770.0 x 10-6 cm3 mol-1

m = 35.14 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.95 7.98 12.903 7.9906 10.15839

2 5.08 19.09 19.4542 12.35687 12.47344

3 10.14 19.31 19.4838 12.42805 12.48292

4 15.05 18.81 18.9431 12.26628 12.30849

5 19.99 18.45 18.5727 12.14849 12.18756

6 29.99 18.107 18.1414 12.0338 12.04522

7 40.00 17.9295 17.9079 11.97467 11.96745

8 50.00 17.8172 17.7628 11.93711 11.91887

9 60.04 17.7392 17.6639 11.91095 11.88564

10 70.05 17.6572 17.5926 11.88339 11.86163

11 80.08 17.6318 17.5386 11.87484 11.84341

12 90.089 17.5972 17.4964 11.86318 11.82916

13 100.1 17.554 17.4625 11.84861 11.81769

14 110.08 17.52 17.4347 11.83713 11.80828

15 120.13 17.4909 17.4113 11.8273 11.80035

16 130.16 17.4592 17.3915 11.81657 11.79364

17 140.18 17.4322 17.3746 11.80743 11.78791

18 150.19 17.41 17.3598 11.79991 11.78289

19 160.19 17.396 17.3469 11.79517 11.77851

20 170.21 17.3765 17.3355 11.78855 11.77464

21 180.23 17.3689 17.3254 11.78598 11.77121

22 190.23 17.3438 17.3163 11.77746 11.76812

23 200.24 17.3315 17.3081 11.77328 11.76533

24 210.15 17.3147 17.3008 11.76757 11.76285

25 220.24 17.3035 17.294 11.76377 11.76054

26 230.25 17.3072 17.2878 11.76502 11.75843

27 240.25 17.295 17.2821 11.76088 11.75649

28 250.25 17.282 17.2769 11.75646 11.75472

29 260.26 17.2788 17.2721 11.75537 11.75309

30 270.26 17.2627 17.2677 11.74989 11.75159

31 280.23 17.2561 17.2636 11.74764 11.7502

32 290.24 17.2568 17.2597 11.74788 11.74887

APPENDICES

Complex MnIII4 (12)

MW = 1384 g/mol, χdia = -650.0 x 10-6 cm3 mol-1

m = 29.59 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.966 5.7165 6.90638 6.76152 7.43198

2 5.094 14.5492 15.6427 10.78696 11.18498

3 9.999 16.7753 16.9447 11.58283 11.64116

4 14.994 16.1334 15.9428 11.35906 11.29176

5 20.004 15.3838 15.2949 11.09203 11.05994

6 29.999 14.3461 14.5037 10.7114 10.77008

7 40 13.7333 14.0042 10.48013 10.58299

8 50.008 13.3568 13.6506 10.33548 10.44853

9 60.035 13.0962 13.385 10.23416 10.34638

10 70.059 12.9027 13.1782 10.15827 10.26615

11 80.056 12.7774 13.0129 10.10882 10.20156

12 90.101 12.6807 12.8769 10.0705 10.14811

13 100.12 12.5933 12.7639 10.03573 10.10348

14 110.13 12.5281 12.6682 10.00972 10.06553

15 120.14 12.47 12.5862 9.98648 10.03291

16 130.16 12.4259 12.5151 9.96881 10.00453

17 140.18 12.3819 12.4529 9.95114 9.97963

18 150.13 12.3487 12.3984 9.93779 9.95777

19 160.19 12.3258 12.3495 9.92858 9.93812

20 170.22 12.3047 12.3058 9.92007 9.92052

21 180.23 12.2882 12.2666 9.91342 9.9047

22 190.23 12.2529 12.2312 9.89917 9.8904

23 200.24 12.2308 12.199 9.89024 9.87737

24 210.24 12.2064 12.1697 9.88037 9.86551

25 220.26 12.1763 12.1427 9.86818 9.85456

26 230.26 12.1583 12.118 9.86088 9.84453

27 240.26 12.129 12.0951 9.84899 9.83522

28 250.25 12.1031 12.074 9.83847 9.82664

29 260.27 12.0814 12.0544 9.82965 9.81866

30 270.26 12.0595 12.0361 9.82074 9.8112

31 280.14 12.05 12.0193 9.81687 9.80435

32 290.26 12.0524 12.0032 9.81785 9.79779

APPENDICES

Complex MnIII4MnII2 (13)

MW = 1774 g/mol, χdia = -740 x 10-6 cm3 mol-1

m = 22.95 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.954 5.71186 5.53098 6.75878 6.6509

2 5.076 8.99394 7.83852 8.48114 7.91765

3 9.994 9.72196 8.43898 8.81772 8.21532

4 15.014 9.67494 8.61716 8.79637 8.30159

5 20.005 9.53456 8.75954 8.73232 8.3699

6 30.001 9.40964 9.09982 8.67493 8.53092

7 39.999 9.55658 9.49414 8.7424 8.71379

8 50.011 9.90966 9.91632 8.90243 8.90543

9 60.046 10.34882 10.35492 9.09756 9.10024

10 70.052 10.80894 10.79858 9.2976 9.29315

11 80.059 11.27654 11.23944 9.49658 9.48095

12 90.105 11.73602 11.67076 9.68813 9.66115

13 100.12 12.1494 12.08298 9.85727 9.83029

14 110.13 12.54018 12.473 10.01455 9.98769

15 120.13 12.88962 12.8384 10.15312 10.13293

16 130.12 13.21522 13.17852 10.28056 10.26627

17 140.19 13.50796 13.49652 10.3938 10.3894

18 150.2 13.78836 13.78898 10.50112 10.50136

19 160.21 14.03658 14.05928 10.59522 10.60379

20 170.21 14.27676 14.30878 10.68548 10.69746

21 180.22 14.49874 14.53964 10.76824 10.78341

22 190.23 14.68712 14.7532 10.83796 10.86232

23 200.24 14.87638 14.95098 10.90757 10.93489

24 210.24 15.03404 15.13426 10.96522 11.00171

25 220.25 15.19804 15.30468 11.02486 11.06347

26 230.25 15.34708 15.4631 11.07879 11.12059

27 240.26 15.47818 15.6109 11.12601 11.17361

28 250.26 15.61206 15.74874 11.17402 11.22283

29 260.27 15.73 15.8778 11.21615 11.26872

30 270.26 15.80874 15.99844 11.24419 11.31145

31 280.24 15.9287 16.11154 11.28677 11.35136

32 290.26 16.06634 16.21826 11.33543 11.38889

APPENDICES

Complex MnIII4MnII2 (14)

MW = 1744 g/mol, χdia = -720 x 10-6 cm3 mol-1

m = 15.34 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.954 5.71186 5.53098 6.75878 6.6509

2 5.076 8.99394 7.83852 8.48114 7.91765

3 9.994 9.72196 8.43898 8.81772 8.21532

4 15.014 9.67494 8.61716 8.79637 8.30159

5 20.005 9.53456 8.75954 8.73232 8.3699

6 30.001 9.40964 9.09982 8.67493 8.53092

7 39.999 9.55658 9.49414 8.7424 8.71379

8 50.011 9.90966 9.91632 8.90243 8.90543

9 60.046 10.34882 10.35492 9.09756 9.10024

10 70.052 10.80894 10.79858 9.2976 9.29315

11 80.059 11.27654 11.23944 9.49658 9.48095

12 90.105 11.73602 11.67076 9.68813 9.66115

13 100.12 12.1494 12.08298 9.85727 9.83029

14 110.13 12.54018 12.473 10.01455 9.98769

15 120.13 12.88962 12.8384 10.15312 10.13293

16 130.12 13.21522 13.17852 10.28056 10.26627

17 140.19 13.50796 13.49652 10.3938 10.3894

18 150.2 13.78836 13.78898 10.50112 10.50136

19 160.21 14.03658 14.05928 10.59522 10.60379

20 170.21 14.27676 14.30878 10.68548 10.69746

21 180.22 14.49874 14.53964 10.76824 10.78341

22 190.23 14.68712 14.7532 10.83796 10.86232

23 200.24 14.87638 14.95098 10.90757 10.93489

24 210.24 15.03404 15.13426 10.96522 11.00171

25 220.25 15.19804 15.30468 11.02486 11.06347

26 230.25 15.34708 15.4631 11.07879 11.12059

27 240.26 15.47818 15.6109 11.12601 11.17361

28 250.26 15.61206 15.74874 11.17402 11.22283

29 260.27 15.73 15.8778 11.21615 11.26872

30 270.26 15.80874 15.99844 11.24419 11.31145

31 280.24 15.9287 16.11154 11.28677 11.35136

32 290.26 16.06634 16.21826 11.33543 11.38889

APPENDICES

Complex CuII6 (15)

MW = 1657 g/mol, χdia = -660 x 10-6 cm3 mol-1

m = 35.32 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.922 0.33836 0.0033 1.64501 0.16246

2 5.19 0.59442 0.1963 2.18035 1.25297

3 9.991 0.61462 0.4496 2.21709 1.89624

4 15.013 0.59928 0.5582 2.18924 2.11288

5 20.005 0.61975 0.6107 2.22633 2.21001

6 30 0.65456 0.6608 2.28799 2.29887

7 40.003 0.68417 0.6847 2.33916 2.33916

8 50.006 0.70997 0.7 2.38286 2.38286

9 60.03 0.7283 0.71 2.41344 2.41344

10 70.051 0.74367 0.72 2.43876 2.43876

11 80.045 0.7599 0.73 2.46523 2.46523

12 90.082 0.76789 0.74 2.47816 2.47816

13 100.12 0.77633 0.74 2.49173 2.49173

14 110.12 0.78415 0.75 2.50426 2.50426

15 120.14 0.79109 0.76 2.51532 2.51532

16 130.16 0.7976 0.76 2.52565 2.52565

17 140.17 0.80391 0.78 2.53561 2.53561

18 150.13 0.81065 0.79 2.54621 2.54621

19 160.2 0.81785 0.8 2.55751 2.55751

20 170.21 0.82507 0.82 2.56877 2.56877

21 180.22 0.83312 0.83 2.58127 2.58127

22 190.22 0.8412 0.84 2.59376 2.59376

23 200.22 0.85044 0.85 2.60796 2.60796

24 210.23 0.85998 0.86 2.62255 2.62255

25 220.25 0.87022 0.88 2.63811 2.63811

26 230.24 0.88141 0.89 2.65503 2.65503

27 240.25 0.8924 0.9 2.67153 2.67153

28 250.25 0.90446 0.92 2.68951 2.68951

29 260.27 0.91742 0.93 2.70871 2.70871

30 270.25 0.93045 0.944 2.72789 2.72789

31 280.25 0.94357 0.956 2.74705 2.74705

32 290.24 0.95801 0.968 2.76799 2.76799

APPENDICES

Complex NiII9 (16)

MW = 2347 g/mol, χdia = -990 x 10-6 cm3 mol-1

m = 24.91 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 1.958 0.43884 0.2031 1.87341 1.27448

2 5.116 0.55179 0.62 2.10071 2.22677

3 10.168 0.69449 0.83 2.35674 2.57643

4 15.043 0.88835 0.99 2.66546 2.81382

5 20.005 1.09873 1.17 2.96432 3.05895

6 30.002 1.49451 1.51 3.45723 3.4751

7 40.003 1.83462 1.83 3.83048 3.82565

8 50.005 2.1308 2.11 4.12811 4.10791

9 60.038 2.38751 2.37 4.3697 4.35365

10 70.053 2.61174 2.6 4.5703 4.56001

11 80.065 2.81625 2.808 4.74586 4.7389

12 90.087 2.99803 2.9972 4.89663 4.89595

13 100.13 3.16516 3.168 5.03127 5.03352

14 110.1 3.31166 3.32 5.14639 5.15286

15 120.14 3.45017 3.46 5.2529 5.26038

16 130.17 3.57094 3.58 5.34405 5.35083

17 140.18 3.68455 3.699 5.4284 5.43903

18 150.18 3.78576 3.8 5.50244 5.51279

19 160.2 3.88302 3.89 5.57268 5.57769

20 170.21 3.96987 3.98 5.63466 5.64184

21 180.22 4.04943 4.06 5.69084 5.69826

22 190.24 4.12616 4.13 5.7445 5.74718

23 200.24 4.19321 4.2 5.79099 5.79568

24 210.16 4.25886 4.26 5.83615 5.83693

25 220.24 4.32103 4.32 5.87859 5.87789

26 230.26 4.37688 4.37 5.91646 5.91181

27 240.26 4.43332 4.42 5.95448 5.94553

28 250.25 4.48225 4.47 5.98725 5.97906

29 260.27 4.52742 4.514 6.01734 6.00842

30 270.26 4.57264 4.56 6.04732 6.03896

31 280.26 4.61571 4.59 6.07573 6.05879

32 290.26 4.66497 4.63 6.10807 6.08513

APPENDICES

Complex CuII9 (17)

MW = 2595 g/mol, χdia = -1260 x 10-6 cm3 mol-1

m = 22.53 mg , H = 1.000 T

T(K) χ.Texp. χ.Tcalc. µexp µcalc.

1 2 0.90783 0.84 2.69452 2.5919

2 5 1.13652 1.222 3.01487 3.12619

3 10 1.32429 1.3644 3.2544 3.30332

4 15 1.40389 1.408 3.35078 3.35568

5 20 1.43277 1.423 3.38507 3.37351

6 30 1.43319 1.4189 3.38557 3.36865

7 40 1.41523 1.4016 3.36429 3.34805

8 50 1.40297 1.3875 3.34968 3.33116

9 60.04 1.4014 1.3835 3.34781 3.32636

10 70.05 1.40066 1.3921 3.34692 3.33668

11 80.06 1.41961 1.414 3.36949 3.36282

12 90.09 1.45108 1.4482 3.40663 3.40325

13 100.09 1.49328 1.4928 3.45581 3.45526

14 110.16 1.54608 1.5462 3.51638 3.51651

15 120.14 1.60616 1.6057 3.58405 3.58353

16 130.16 1.66997 1.6701 3.65455 3.65469

17 140.13 1.739 1.7372 3.72932 3.72739

18 150.19 1.8095 1.8068 3.80416 3.80132

19 160.19 1.88111 1.8767 3.8787 3.87415

20 170.2 1.95163 1.9467 3.95074 3.94574

21 180.21 2.02169 2.016 4.02102 4.01536

22 190.23 2.09067 2.084 4.08905 4.08252

23 200.24 2.15602 2.1567 4.15246 4.15312

24 210.24 2.22219 2.2153 4.2157 4.20916

25 220.25 2.28414 2.2781 4.27406 4.26841

26 230.24 2.33785 2.3387 4.32402 4.32481

27 240.24 2.39403 2.3971 4.37567 4.37847

28 250.25 2.44631 2.4535 4.42319 4.42968

29 260.26 2.4959 2.5 4.46779 4.47146

30 270.27 2.54654 2.55 4.51289 4.51595

31 280.26 2.59664 2.609 4.55707 4.5679

32 290.26 2.65603 2.6575 4.60889 4.61016