Dy4, Dy5, and Ho2 Complexes of an N3O2 Aminophenol Donor: A Dy5-µ3-Peroxide Single Molecule Magnet

Citation: Corredoira-Vázquez, J.; Oreiro-Martínez, P.; Nieto-Pastoriza, D.; García-Deibe, A.M.; Sanmartín-Matalobos, J.; Fondo, M. Dy4,Dy 5, and Ho2Complexes of an N3O2Aminophenol Donor: A Dy5-μ3-Peroxide Single Molecule Magnet. Int. J. Mol. Sci. 2023,24, 9061. https://doi.org/10.3390/ ijms24109061 Academic Editors: Wolfgang Linert and JoséMartínez-Lillo Received: 31 March 2023 Revised: 26 April 2023 Accepted: 16 May 2023 Published: 21 May 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). International Journal of Molecular Sciences Article Dy4,Dy 5, and Ho2Complexes of an N3O2Aminophenol Donor: ADy 5-μ3-Peroxide Single Molecule Magnet Julio Corredoira-Vázquez 1,2 , Paula Oreiro-Martínez 1, Daniel Nieto-Pastoriza 1, Ana M. García-Deibe 1, Jesús Sanmartín-Matalobos 1,3 and Matilde Fondo 1,* 1Departamento de Química Inorgánica, Facultade de Química, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain 2Phantom-g, CICECO—Aveiro Institute of Materials, Department of Physics, University of Aveiro, 3810-193 Aveiro, Portugal 3Institute of Materials (iMATUS), Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain *Correspondence: [email protected] Abstract: The reactivity of the new flexible potentially pentadentate N 3 O 2 aminophenol ligand H 4 L r (2,2-((pyridine-2,6-diylbis(methylene))bis(azanediyl))diphenol) towards different dysprosium salts and holmium(III) nitrate was investigated. Accordingly, this reactivity seems to greatly depend on the metal ion and salt employed. In this way, the reaction of H 4 L r with dysprosium(III) chloride in air leads to the oxo-bridged tetranuclear complex [Dy 4 (H 2 L r ) 3 (Cl) 4 ( μ3 -O)(EtOH) 2 (H 2 O) 2 ] · 2EtOH · H 2 O ( 1· 2EtOH · H 2 O), while the same reaction just changing the chloride salt by the nitrate one renders the peroxo-bridged pentanuclear compound [Dy5(H2Lr)2(H2.5Lr)2(NO3)4(μ3-O2)2]·2H2O(2·2H2O), where both peroxo ligands seem to come from the fixation and reduction of atmospheric oxygen. However, if holmium(III) nitrate is used instead of dysprosium(III) nitrate, no evidence of a peroxide ligand is observed, and the dinuclear complex {[Ho 2 (H 2 L r )(H 3 L r )(NO 3 ) 2 (H 2 O) 2 ](NO 3 )} 2.5H 2 O ( 3· 2.5H 2 O) is isolated. The three complexes were unequivocally characterized by X-ray diffraction techniques, and their magnetic properties were analyzed. Thus, while the Dy 4 and Ho 2 complexes do not show magnet-like behavior even in the presence of an external magnetic field, 2· 2H 2 O is a single molecule magnet, with an U eff barrier of 61.2 K (43.2 cm −1 ). This is the first homonuclear lanthanoid peroxide SMM, which also shows the highest barrier among the reported 4f/3d peroxide zero field SMMs to date. Keywords: lanthanoid; SMM; peroxide ligand; N3O2aminophenol 1. Introduction Molecular magnetism is a growing field in which single-molecule magnets (SMMs) occupy a preferential place. The great interest in SMMs is based on their potential applications, which include ultrahigh-density information storage or quantum computing [1,2]. In contrast to classical magnets, the molecular nature of SMMs offers unique properties that could enable unprecedented information storage speed, and processing densities [ 2 ]. The main requirement to achieve this end is the ability to block the magnetization of the molecule at elevated temperatures, a goal that has so far not been achieved. The high intrinsic spin and anisotropy of lanthanoids make them preferred candidates in the search for molecule magnets with enriched properties. Accordingly, since the discovery of the first single ion magnet (SIM) in 2003 [ 3 ], the performance of SMMs has steadily improved. Thus, the best functioning magnets are mononuclear Dy III compounds, so that, at present, the blocking temperature (T B ) record of 80 K is held by [(Cp iPr5 )Dy(Cp*)][B(C 6 F 5 ) 4 ][ 4 ]. However, this kind of metallocene is unstable in air, and the T B record for an air-stable compound is held by [Dy(bmbpen-F)Br] (bmbpen-F = N,N’-bis-(5-methyl-2-hydroxybenzyl)-N,N’-bis(5- fluoro-2-methylpyridyl)ethylenediamine) [ 5 ] at 36 K, although the highest energy barrier Int. J. Mol. Sci. 2023,24, 9061. https://doi.org/10.3390/ijms24109061 https://www.mdpi.com/journal/ijms Int. J. Mol. Sci. 2023,24, 9061 2of16 (>1800 K) for an air-stable SMM is owned by a Dy III SIM with hexagonal bipyramidal geometry [6]. Therefore, as it is logical, and based on Long’s theory [ 7 ], it seems easier to control the anisotropy of mononuclear complexes, which leads to better magnetic results. However, even so, the performance of magnets with more than one metal center is also improving significantly. Thus, it has recently been described that the dinuclear mixed-valent complex [(Cp iPr5 ) 2 Dy 2 I 3 ][ 8 ], which features metal-to-metal bonding, shows an enormous coercive magnetic field, and hysteresis up to 80 K, although it is also unstable in air. In addition, the Dy–Sc nitride cluster fullerene Dy 2 ScN@C80-I h , with a nitrogen bridge between the Dy III ions, presents an U eff barrier of ca. 1735 K [ 9 ], very close to the record for an air-stable SIM. In addition, among air stable complexes, we have described the phenoxo-bridged dinuclear dysprosium complex with the highest energy barrier for spin reversal for this type of compound to date [ 10 ]. This was achieved with an N 4 O 3 aminophenol donor, a ligand that also leads to fluoride-bridged complexes, some of them with unprecedented structural and magnetic features [ 11 ]. Accordingly, following this line of work, this paper describes the versatility in the coordination chemistry of a new pentadentate N 3 O 2 aminophenol with Dy III and Ho III , which includes the isolation of a rare Dy III pentanuclear peroxo-complex, and the study of the magnetic properties of all the obtained compounds. 2. Results and Discussion 2.1. Synthesis H 4 L r , which is original from this work, is obtained by reducing the previously reported Schiff base H 2 L[ 12 – 14 ] with sodium borohydride, as summarized in Scheme 1. The analytical and spectroscopic studies of H 4 L r (Experimental section, and Figure S1) completely agreed with its isolation with high purity. Scheme 1. Synthetic route for the isolation of H4Lrand its metal complexes. The reactivity of H 4 L r towards lanthanoid salts in air seems to greatly depend on the lanthanoid employed but also on the anion of the metal salt, as shown in Scheme 1. Accordingly, when the ligand reacts with dysprosium(III) chloride in a basic medium, single crystals of the Dy 4 complex 1· 2EtOH · H 2 O with a μ3 -oxide bridge are isolated. The composition of these crystals is approximate, given that SQUEEZE [ 15 ] has to be applied due to the great disorder of the trapped solvent. Thus, these crystals seem to lose the ethanol solvate on drying, and the elemental analyses of the dried crystals agree with formula 1·5H2O. Int. J. Mol. Sci. 2023,24, 9061 3of16 When the aminophenol ligand reacts with dysprosium(III) nitrate instead of chloride, the peroxo-bridged Dy 5 complex 2· 2H 2 O is obtained. Nevertheless, if holmium(III) nitrate is used in the place of the dysprosium(III) one, the dinuclear holmium compound 3· 2.5H 2 O, without any evidence of peroxide as ligand, is separated. Accordingly, this indicates that the formation of the peroxo donor is achieved in the presence of nitrate and Dy III but not of Ho III . This may seem somewhat strange since one would expect the chemical behavior of Dy III and Ho III to be similar. In this respect, we should point out that a search was made in CSD [ 16 ] for crystallographically characterized peroxo-lanthanoid complexes in which there is no doubt as to the nature of the oxygenated ligand. This search show that homonuclear peroxo-complexes has been obtained from air with Ce IV [ 17 – 22 ], Nd III [ 23 – 25 ], Sm III [ 26 – 28 ], Eu III [ 23 , 24 , 26 ], Gd III [ 26 ], Tb III [ 29 ], Dy III ,[ 30 ], Yb III [ 23 , 31 – 34 ], and Lu III [ 35 ] ions, in addition to 3d/4f M 3 Ln 3 (M = Ni, Cu or Zn; Ln = Gd, Tb, or Dy) [ 36 , 37 ] and Zn 4 Ln 7 (Ln = Gd, Dy) peroxo compounds [ 38 ]. However, as far as we know, no holmium peroxo-complexes have been obtained by interaction with oxygen. In addition, some other lanthanoid peroxo-complexes of the mentioned ions or La III have been mostly isolated from peroxides as reagents [ 39 – 42 ]. Among these, it is worth noting that there is a series of peroxo-complexes of Gd, Tb, Dy, and Er with the same ligand, but not the Ho one [ 42 ]. Accordingly, based on this literature search, in which not a single peroxo-Ho complex was found, the results described here are not surprising, and, as expected, the interaction of HoIII with the peroxide ligand does not appear to be favored. Attempts were made to determine the origin of the peroxide species. Consequently, the reaction of H 4 L r and Dy(NO 3 ) 3· 6H 2 O was repeated in a strict inert atmosphere under Ar. Unfortunately, it was not possible to obtain single crystals of this sample of sufficient quality to be solved. However, the elemental analysis of this compound seems to be in agreement with the empirical formula {[Dy 2 (H 2 L r )(H 3 L r )(NO 3 ) 2 (H 2 O) 2 ](NO 3 )} · 2EtOH · H 2 O ( 4· 2EtOH · H 2 O), similar to that of the holmium complex 3· 2.5H 2 O. Obviously, in the absence of a single crystal structure, it does not make sense to speculate more on the possible structure of this compound, but IR spectroscopy seems to help determine the nature of the species. Thus, the IR spectrum of 2· 2H 2 O (Figure S2) shows a band at 831 cm −1 , absent in the spectra of the nitrate holmium complex 3· 2.5H 2 O and of the nitrate dysprosium compound 4· 2EtOH · H 2 O. The position, shape, and intensity of this band seems to agree with the vibration of the peroxide ligand [ 25 , 37 , 38 ]. The presence of this donor is also confirmed by the Raman spectrum, which shows a weak peak at 831 cm −1 (Figure S3), whose shape and intensity are similar to that previously described for other lanthanoid peroxo-complexes [ 18 , 37 ]. In addition, the IR spectroscopy seems to indicate that the peroxo group does not form in the absence of air, as this band is not present in the spectrum of 4· 2EtOH · H 2 O (Figure S2). However, additionally, when the mother liquor from the synthesis of 4· 2EtOH · H 2 O in inert atmosphere is left in air, a small portion of a new solid 5 precipitates, whose IR spectrum is identical to that of 2· 2H 2 O between 2000 and 500 cm −1 , and it again shows the presence of the band at 831 cm −1 (Figure S4). Accordingly, the peroxide ligand seems to come from air reduction. 2.2. X-ray Diffraction Studies Single crystals of 1· 2EtOH · H 2 O- 3· 2.5H 2 O were obtained as detailed above. The experimental details of data acquisition and resolution are summarized in Table S1. Dy 4 (H 2 L r ) 3 (Cl) 4 ( μ3 -O)(EtOH) 2 (H 2 O) 2 ] · 2EtOH · H 2 O( 1· 2EtOH · H 2 O). An ellipsoid diagram for 1 is shown in Figure 1, and their main bond distances and angles are listed in Table S2. Int. J. Mol. Sci. 2023,24, 9061 4of16 Figure 1. Ellipsoids diagram (50% probability) for [Dy 4 (H 2 Lr) 3 (Cl) 4 ( μ3 -O)(EtOH) 2 (H 2 O) 2 ]( 1 ). Only metal ions and their cores are labeled, for clarity. The unit cell of 1· 2EtOH · H 2 O contains neutral molecules of [Dy 4 (H 2 L r ) 3 (Cl) 4 ( μ3 -O)(EtOH) 2 (H 2 O) 2 ]( 1 ) and water and ethanol as solvates. It should be noted that SQUEEZE [ 15 ] was applied to these crystals to correctly solve the structure due to the high disorder of the solvent. Accordingly, the composition of the solvates in the crystals is inexact. [Dy 4 (H 2 L r ) 3 (Cl) 4 ( μ3 -O)(EtOH) 2 (H 2 O) 2 ] does not contain symmetry elements. However, in order to simplify its description, the tetranuclear compound can be considered as formed from 3 mononuclear building blocks, each of which uses some of its donor atoms to bind a fourth Dy III ion. Two of these three mononuclear units, those containing Dy1 and Dy3, which we will therefore call 1 .1 and 1 .3, are chemically equivalent but crystallographically different, and written as the neutral fragments [Dy(H 2 L r )(Cl)(H 2 O)] (Figure 2a). The mononuclear unit containing Dy2, which we call 1 .2, is the monoanionic fragment [Dy(H2Lr)(Cl)2(EtOH)]−(Figure 2b). Figure 2. Mononuclear blocks that are present in 1 :( a ) schematic representation of neutral 1 .1 and 1 .3 blocks; ( b ) schematic representation of the monoanionic 1 .2 block. The bending of the ligand is not shown in the figure, only its coordination mode, to facilitate the understanding of the structure. In all the mononuclear moieties, the phenol oxygen atoms of the ligand are deprotonated, and the dianionic aminophenol acts as a pentadentate N 3 O 2 donor. In addition, in fragments 1 .1 and 1 .3, a water molecule and a chloride ligand also bind the metal ion, leading to coordination number 7. For fragment 1 .3, two chloride anions and an ethanol donor from the solvent of the reaction are also coordinated to the dysprosium atom, leading to an octacoordinated environment. These three mononuclear fragments are joined among them and to Dy4 by means of various bridges, completing their coordination spheres. Accordingly, Dy1 reachs coordina- Int. J. Mol. Sci. 2023,24, 9061 5of16 tion number 8 by binding to an O 2− bridge (O1), while Dy3 reachs coordination number 9 by also binding to O1 and to a phenolate oxygen atom (O11) of one of the ligand arms of unit 1 .1. Therefore, between units 1 .1 and 1 .3, there is a double oxygen bridge (phenolate O11 and oxo O1, Figure 3), and this Dy2O2core shows Dy-O-Dy angles close to 110◦. Figure 3. Dy 4 core environment for 1 , showing only the oxygen bridges. The intermolecular distances between bridged Dy atoms are also shown. Units 1 .1, 1 .2, and 1 .3 employ all their phenolic oxygen atoms that were not previously used in coordinated bonds (two in 1 .2 and 1 .3, and one in 1 .1, a total of five) to bind the fourth dysprosium ion Dy4 (Figures 1and 3). This Dy4 center is further bonded to the oxo bridge O1 and to one ethanol ligand, thus reaching coordination number 7. Accordingly, as a consequence of the described features, as shown in Figure 3, the pairs Dy1 and Dy4, and Dy2 and Dy4, are also double bridged, and the Dy 2 O 2 groups show distances comparable to those found between Dy1 and Dy3, with similar Dy-O-Dy angles. However, Dy3 and Dy4 are triple bridged by two phenolic oxygen atoms and by an oxygen atom of the oxo group (O1), which at this point acts as a μ3 bridge, linking Dy1, Dy3, and Dy4. This triple bridged Dy 2 O 3 core, as would be expected, shows the shortest distance between dysprosium atoms (Figure 3), with much shorter Dy-O-Dy angles, between 96.3 and 98.3◦. As a result of the situation described, the three [H 2 L r ] 2− ligands show two different coordination modes. In all three cases, it acts as pentadentate, but in one case (when the ligand inserts Dy1 in its N 3 O 2 pocket) it is a bridging μ2 donor, and in two others (when it inserts Dy2 or Dy3 in the pocket), a μ3donor (Figure 4). Figure 4. Coordination modes of the pentadentate aminophenol ligand in 1. According to the discussed features, the coordination numbers of dysprosium atoms are different: 8 for Dy1 and Dy2, 9 for Dy3, and 7 for Dy4. Calculations of the distortion of the polyhedra with respect to the ideals for 8, 9, or 7 vertices with the SHAPE program [ 43 ] (Table S3) show that the geometry that best represented the environment of Dy1 and Dy2 is a triangular dodecahedron, for Dy3 a “muffin”, and for Dy4 a capped octahedron. All distances and bond angles in these polyhedra are within their normal range [ 10 , 13 , 14 ] and do not merit further consideration. Finally, it should be noted that one of the amine nitrogen atoms and one of the chlorine ligands per tetranuclear molecule are involved in a weak intermolecular hydrogen bond, which expands this tetranuclear unit into a zig-zag chain. [Dy 5 (H 2 L) 2 (H 2.5 L) 2 (NO 3 ) 4 ( μ3 -O 2 ) 2 ] · 2H 2 O( 2· 2H 2 O). An ellipsoid diagram for 2 is shown in Figure 5, and their main bond distances and angles are listed in Table S4. Int. J. Mol. Sci. 2023,24, 9061 6of16 Figure 5. Ellipsoids diagram (50% probability) for [Dy 5 (H 2 L) 2 (H 2.5 L) 2 (NO 3 ) 4 ( μ3 -O 2 ) 2 ]. Only metal ions and their cores of the asymmetric unit are labeled, for clarity. The unit cell of 2· 2H 2 O contains molecules of the neutral pentanuclear complex [Dy 5 (H 2 L r ) 2 (H 2.5 L r ) 2 (NO 3 ) 4 ( μ3 -O 2 ) 2 ], together with water as a solvate. The asymmetric unit of the crystal contains only half of the complex molecule, the other half being generated by an improper rotation axis ( − x+1,y, − z+ 1 2 ) passing through Dy3. Thus, each molecule of this neutral complex can be understood as two dinuclear [Dy(H 2 L r )(NO 3 )( μ2 - O 2 )Dy(H 2.5 L r )(NO 3 )] 1.5− blocks (Figure 6), which join a fifth Dy 3+ ion (Dy3) between them, using four phenolate groups (one per aminophenol ligand, O11 and O21), and the two (one per block) peroxide ligands (O1-O2), as shown in Figure 7. This leads to the aminophenol acting as a μ2bridge but in a different way (μ2-κ5:κ1, Figure 7)from1. Figure 6. Balls and sticks representation for a dinuclear block [Dy 2 (H 2 L r )(H 2.5 L r )(NO 3 ) 2 ( μ2 -O 2 )] 1.5− . Only the metal ions and their coordination spheres are represented as balls for the shake of clarity. Int. J. Mol. Sci. 2023,24, 9061 7of16 Figure 7. ( Left ) Ball diagram showing the bridges between the Dy 3+ centres. The μ3 - κ2 : κ2 : κ2 bond for the peroxide donors between Dy1, Dy2, and Dy3 is shown, with distances d(Dy1 ··· Dy2) = 4.2636(6) Å; d(Dy1 ··· Dy3) = 3.6317(4) Å and d(Dy2 ··· Dy3) = 3.5923(4) Å. ( Right ) Coordination mode for the aminophenol in 2. The flexion of the ligand is not represented for the shake of clarity. In turn, the respective dinuclear blocks can be considered constructed from two mononuclear units, [Dy(H 2.5 L r )(NO 3 )] 0.5− and [Dy(H 2 L r )(NO 3 )] − , which contain Dy1 and Dy2, respectively. The main difference between the units lies in the fact that one of the phenolic oxygen atoms (O12) is semi-protonated in one of the units but not in the other. At the same time, in each mononuclear unit, the aminophenol ligand links a Dy III center in its N 3 O 2 pocket, as in 1 . Each metal center also binds a nitrate ligand, which acts as a bidentate chelate donor (Figure 6). In addition, both oxygen atoms of the peroxide group (O1 and O2) are coordinated in side-on mode to the two dysprosium atoms, with a partial coordination mode μ2 - κ2 : κ2 in each dinuclear block (Figure 6). Thus, in these dinuclear entities, the dysprosium atoms are nonacoordinated, in N 3 O 6 environments. Calculations with the SHAPE program (Table S3) [ 43 ] indicate that the geometry around the dysprosium atoms is spherical capped square antiprism. The central dysprosium atom (Dy3, see Figure 7) is in a highly distorted O 8 environment. This is achieved by means of the four mentioned bridging phenolate O-atoms, and two peroxide ligands acting as μ3 - κ2 : κ2 : κ2 bridges, and according to SHAPE measurements (Table S3) [43], this environment can be described as a biaugmented trigonal prism. The coordination mode of the O 22− ligand is quite common for lanthanoid complexes with peroxide as donor [ 25 , 36 – 38 , 42 ], and all the distances between this donor and the pentadentate ligand are within their normal ranges [ 10 , 13 , 14 , 36 – 38 , 42 ]. In addition, the dysprosium ions within the dinuclear subunits bridged by the O 22− donor are at distances Dy1 ··· Dy2 of 4.2636(6) Å, with Dy1-O peroxide -Dy2 angles of ca. 129 ◦ . A double hydrogen bond between one oxygen atom of the nitrate group joined to Dy1 and one amine nitrogen atom joined to Dy2 and vice versa (Figure 6) also contributes to shortening this distance. Dy1 ··· Dy3 and Dy2 ··· Dy3 are triple bridged by the peroxide and one phenol oxygen atom (Figure 7). This leads to shorter Dy1 ··· Dy3 and Dy2 ··· Dy3 distances, ca. 3.6 Å, with Dy-O-Dy angles in the range 97.6–103.1◦. [Ho 2 (H 2 L r )(H 3 L r )(NO 3 ) 2 (H 2 O) 2 ](NO 3 ) · 2 · 5H 2 O( 3· 2.5H 2 O). The unit cell of 3· 2.5H 2 O contains [Ho 2 (H 2 L r )(H 3 L r )(NO 3 ) 2 (H 2 O) 2 ] + cations, NO 3- anions, and water as solvate. An ellipsoid diagram for 3 is shown in Figure 8, and the principal bond distances and angles are listed in Table S5. Int. J. Mol. Sci. 2023,24, 9061 8of16 Figure 8. Ellipsoids diagram (50% probability) for the cation [Ho 2 (H 2 L r )(H 3 L r )(NO 3 ) 2 (H 2 O) 2 ] + in 3 . Only metal ions and their cores are labeled, for clarity. The dinuclear cationic complex [Ho 2 (H 2 L r )(H 3 L r )(NO 3 ) 2 (H 2 O) 2 ] + can be considered assembled from two mononuclear blocks: cationic [Ho(H 3 L r )(NO 3 )(H 2 O)] + , which we call 3 .1, and neutral [Ho(H 2 L r )(NO 3 )(H 2 O)], which we call 3 .2. Both blocks are similar (Figure 9), the main difference being that in 3 .1 one of the phenolic oxygen atoms is protonated, while in 3 .2 both are deprotonated. Apart from this difference, in 3 .1 and 3 .2, the pentadentate ligand acts as usual, using its N3O2donor set to link the DyIII center. Figure 9. Schematic representation of the blocks [Ho(H 3 L r )(NO 3 )(H 2 O)] + ( 3 .1, R = H, n = 1) and [Ho(H 2 L r )(NO 3 )(H 2 O)] ( 3 .2, R does not exist, n = 0). The flexion of the ligand is not represented for the shake of clarity. In the two blocks, the holmium center additionally binds to one nitrate ligand in a bidentate chelate mode and to one water molecule (Figure 9). Units 3 .1 and 3 .2 join each other using each one of the blocks a deprotonated phenolic oxygen to act as a bridge between the Ho1 and Ho2 centers. Thus, the aminophenol ligands also acts as μ2 - κ5 : κ1 bridges, as in 2 . Therefore, this double phenolate bridge leads to a Ho 2 O 2 core, with a Ho···Ho distance of 3.8091(2) Å, and Ho-O-Ho angles close to 109.7◦(Figure 8). As a result of the described situation, the metal ions are in both cases nonacoordinate, and calculations performed with the SHAPE program to see the degree of distortion with respect to an ideal 9-vertex polyhedron show that the geometry in the environment of the metal centers is somewhat different. Thus, for Ho1, the environment is close to a square capped antiprism, distorted toward a spherical tricapped trigonal prism, while for Ho2, Int. J. Mol. Sci. 2023,24, 9061 9of16 the geometry is “muffin” distorted toward a square capped antiprism. The distances and bond angles of these olyhedral are within their normal range and do not merit further consideration [10]. Moreover, powder X-ray diffraction studies for crude samples of 2· 2H 2 O and 3· 2.5H 2 O (Figures S5 and S6) prove that these microcrystalline samples are the same compounds as the single crystals. The powder diffractogram for 1· 5H 2 O was not recorded, given that SQUEZZE was applied to the single crystals, and thus the solvates of the crystals for creating a theoretical diffractogram and those of the crude sample are different, thus preventing an accurate comparison of the experimental and theoretical diffractograms. 2.3. Magnetic Properties Susceptibility magnetic measurements were recorded for 1· 5H 2 O- 3· 2.5H 2 O between 2 and 300 K. The χMTvs. Tplots for the three complexes are shown in Figure 10. (a) (b) (c) Figure 10. χMTvs. Tfor: (a)1·5H2O; (b)2·2H2O; (c)3·2.5H2O. Insets: M/NμBvs. Hat2K. The χM Tvalues at 300 K are 55.2 cm 3 Kmol −1 for 1· 5H 2 O, 66.5 cm 3 Kmol −1 for 2· 2H 2 O, and 28.8 cm 3 Kmol −1 for 3· 2.5H 2 O, which are reasonably close to the expected ones for two Ho 3+ (28.14 cm 3 Kmol −1 ), four (56.68 cm 3 Kmol −1 ), or five (70.85 cm 3 Kmol −1 )Dy 3+ uncoupled ions at room temperature. 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