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Coun e ion in luence on he N–I–N halogen bond
Bedin, Michele; Ka im, Ala i; Rei i, Ma cus; Ca lsson, Anna-Ca in C.; Topic, Filip;
Ce ina, Ma io; Pan, Fang ang; Ha el, Vacla ; Al-Ame i, Fa ima; Sindela , Vladimi ;
Rissanen, Ka i; G ä ens ein, Jü gen; E dély, Má é
Bedin, M., Ka im, A., Rei i, M., Ca lsson, A.-C. C., Topic, F., Ce ina, M., Pan, F., Ha el,
V., Al-Ame i, F., Sindela , V., Rissanen, K., G ä ens ein, J., & E dély, M. (2015).
Coun e ion in luence on he N–I–N halogen bond. Chemical Science, 6(7), 3746-3756.
h ps://doi.o g/10.1039/C5SC01053E
2015
Coun e ion influence on he N–I–N halogen bond†
Michele Bedin,‡
a
Ala i Ka im,‡
a
Ma cus Rei i,
a
Anna-Ca in C. Ca lsson,
a
Filip Topi´
c,
b
Ma io Ce ina,
be
Fang ang Pan,
b
Vacla Ha el,
c
Fa ima Al-Ame i,
a
Vladimi Sindela ,
c
Ka i Rissanen,
b
J¨
u gen G ¨
a ens ein
a
and M´
a ´
e E d´
elyi*
ad
A de ailed in es iga ion o he influence o coun e ions on he [N–I–N]
+
halogen bond in solu ion, in he
solid s a e and in silico is p esen ed. T ansla ional diffusion coefficien s indica e close a achmen o
coun e ions o he ca ionic, h ee-cen e halogen bond in dichlo ome hane solu ion. Iso opic
pe u ba ion o equilib ium NMR s udies pe o med on iso opologue mix u es o egioselec i ely
deu e a ed and nondeu e a ed analogues o he model sys em showed ha he coun e ion is incapable
o al e ing he symme y o he [N–I–N]
+
halogen bond. This symme y emains e en in he p esence o
an un a o able geome ic es ain . A high p e e ence o he symme ic geome y was ound also in he
solid s a e by single c ys al X- ay c ys allog aphy. Molecula sys ems encompassing weakly coo dina ing
coun e ions beha e simila ly o he co esponding sil e (I) cen e ed coo dina ion complexes. In con as ,
sys ems possessing mode a ely o s ongly coo dina ing anions show a dis inc ly diffe en beha io . Such
sil e (I) complexes a e con e ed in o mul i-coo dina e geome ies wi h s ong Ag–O bonds, whe eas
he iodine cen e ed sys ems emain linea and lack di ec cha ge ans e in e ac ion wi h he
coun e ion, as e ified by
15
N NMR and DFT compu a ion. This sugges s ha he [N–I–N]
+
halogen bond
may no be sa is ac o ily desc ibed in e ms o a pu e coo dina ion bond ypical o ansi ion me al
complexes, bu as a seconda y bond wi h a subs an ial cha ge- ans e cha ac e .
In oduc ion
Coun e ions play impo an oles in chemis y, o example in
he modula ion o o ganoca alysis,
1,2
chemical eac ions' ene gy
p oles,
3,4
me al clus e a oma ici y,
5
spec oscopic p ope ies
o o ganic compounds,
6
su ac an micelliza ion,
7
memb ane
pe mea ion,
8
gela ion,
9
sup amolecula assemblies,
10–12
c ys al
s uc u e,
13
and ch oma og aphic sepa a ion.
14
A concei able
inuence o coun e ions on he s eng h and geome y o
halogen bonding has, howe e , so a ba ely ecei ed any
a en ion.
15–17
Halogen bonding has ecen ly been dened,
18
and
has a ac ed as in e es due o i s immense po en ial o
p o ide a no el ool o sup amolecula chemis y,
19,20
c ys al
enginee ing,
21,22
anion ecogni ion,
23,24
o ganic syn hesis,
25
s uc u al biology,
26
medicinal chemis y and chemical
biology,
27
o ins ance.
Th ee-cen e halogen bonds,
15
some imes also e med coo -
dina i e halogen bonds,
28,29
a e o med by he simul aneous
in e ac ion o an elec ophilic halogen (X) wi h wo elec on
dono unc ionali ies (D). The h ee in e ac ing a oms may be
a anged in an asymme ic [D–X/D]
+
, o in a symme ic [D/
X/D]
+
geome y. O hese, he o me is bes desc ibed by a
double well, whe eas he la e by a single well ene gy po en-
ial.
30
The asymme ic a angemen ha encompasses a sho e
and s onge co alen bond (D
d+
–X), and a weake and longe
halogen bond (D
d
/X) is mo e pola han he one possessing a
symme ic geome y and, acco dingly, a symme ic cha ge
dis ibu ion (D
d
/X
d+
/
d
D). S ong, asymme ic coo dina ion
o a coun e ion may a o he o ma ion o he asymme ic,
mo e pola geome y o e he symme ic, less pola one. The
asymme y o he analogous h ee-cen e [N–H–N]
+
hyd ogen
bond
31
has been pa ly a ibu ed o he pola izing effec o he
coun e ion.
32
Limbach e al. epo ed he size and cha ge
delocaliza ion dependen effec o coun e ions on he symme y
o low ba ie hyd ogen bonds.
33
Whe he a coun e ion is
capable o desymme izing he [N–I–N]
+
halogen bond depends
on he in insic ene ge ic p e e ence o he halogen bond o he
symme ic geome y
30
as well as on he p ope ies o he
coun e ion.
a
Depa men o Chemis y and Molecula Biology, Uni e si y o Go henbu g, SE-412 96
Go henbu g, Sweden. E-mail: [email p o ec ed]; Tel: +46-31-786 9033
b
Uni e si y o Jy askyla, Depa men o Chemis y, Nanoscience Cen e , P.O. Box. 35,
FI-40014 Uni e si y o Jy askyla, Finland
c
Depa men o Chemis y and RECETOX, Masa yk Uni e si y, Kamenice 5, 625 00
B no, Czech Republic
d
The Swedish NMR Cen e, Medicina ega an 5, SE-413 90 Go henbu g, Sweden
e
Depa men o Applied Chemis y, Facul y o Tex ile Technology, Uni e si y o Zag eb,
P ilaz ba una Filipo i´
ca 28a, HR-10000 Zag eb, C oa ia
†Elec onic supplemen a y in o ma ion (ESI) a ailable: Expe imen al de ails o
syn hesis, compound cha ac e isa ion, IPE NMR measu emen s, compu a ional
and c ys allog aphic p ocedu es, and c ys al da a o 1-Ag/I o 7-Ag/I,and12-Ag.
CCDC 1045981–1045995. Fo ESI and c ys allog aphic da a in CIF o o he
elec onic o ma see DOI: 10.1039/c5sc01053e
‡These au ho s con ibu ed equally o his wo k.
Ci e his: Chem. Sci.,2015,6,3746
Recei ed 23 d Ma ch 2015
Accep ed 20 h Ap il 2015
DOI: 10.1039/c5sc01053e
www. sc.o g/chemicalscience
3746 |Chem. Sci.,2015,6,3746–3756 This jou nal is © The Royal Socie y o Chemis y 2015
Chemical
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Ea ly solid s a e
14
N nuclea quad upole esonance (NQR)
and in a ed s udies sugges ed
34
ha he N–B bonds o
[bis(py idine)b omine]
+
a e equi alen o i s hexauo ophospha e
sal , bu nonequi alen o i s pe chlo a e and ib omide sal s.
The loss o cen osymme y in he la e wo may be in e p e ed as
a consequence o c ys al packing o ces in combina ion wi h he
diffe en coo dina ion s eng h o a ious coun e ions. Al e na-
i ely, i may be explained by he highly compa able ene gies o he
symme ic and he asymme ic geome ies. Howe e , bo h in e -
p e a ions a e deba able. Diffe en N–B bond leng hs, 2.120(3) ˚
A
and 2.156(3) ˚
A, we e epo ed o he analogous [bis(quinuclidine)
b omine]
+
e auo obo a e complex in he solid s a e.
35
Fo he
analogous iodine cen e ed py idine sal s no analogous coun-
e ion effec s ha e ye been epo ed. Such [N–X–N]
+
complexes
a e common syn he ic eagen s,
36–41
whose eac i i y is ema k-
ably sensi i e o minu e s uc u al
42
and en i onmen al
changes.
41
In con as o he de ailed knowledge collec ed on he
inuence o en i onmen al ac o s on he closely ela ed h ee-
cen e hyd ogen bonds,
32
simila effec s on halogen bonds ha e
so a been assessed o a much lesse ex en . As pa o ou
ongoing in es iga ion o he h ee-cen e halogen bond,
30,43
he
inuence o he coun e ion on he s eng h and geome y o he
in e ac ion in solu ion and in he solid s a e is add essed
he ein.
Resul s and discussion
[Bis(py idine)iodine]
+
complexes
44
and hei s uc u ally closely
ela ed, geome ically es ained 1,2-bis(py idin-2-yle hynyl)
benzene analogues p o ide e sa ile models o he in es iga-
ion o he s uc u e and p ope ies o h ee-cen e halogen
bonds,
15,30,38,39,43,45,46
and we e he e o e u ilized in his s udy. In
o de o e alua e he coun e ion's abili y o modula e he
geome y o he iodine cen e ed, h ee-cen e halogen bond, a
se ies o anions o a ying size, cha ge dis ibu ion and coo -
dina ion s eng h we e explo ed. Besides he sphe ical, weakly
coo dina ing anions
12
BF
4

, ClO
4

, and PF
6

ha ha e p e i-
ously been sugges ed
34,35
o inuence he geome y o he
ela ed [bis(py idine)b omine]
+
complex, he weakly coo di-
na ing SbF
6

, he mode a ely coo dina ing T O

and TsO

, and
he small and s ongly coo dina ing
10,12
NO
3

and CF
3
CO
2

we e assessed (Fig. 1). To ensu e igh coo dina ion,
45
dichlo ome hane was chosen as sol en o he solu ion s udies.
By sca enging he coun e ion wi h he bambusu il Bn
12
BU[6],
47,48
he “coun e ion- ee”[N–I–N]
+
complex was also in es iga ed.
As he h ee-cen e halogen bond was p oposed o be essen ially
analogous o he coo dina ion bond o sil e (I) complexes,
28,29
and as iodine(I) esembles sil e (I) in i s ionic adius (I
+
: 1.33 ˚
A,
Ag
+
: 1.29 ˚
A) and in he linea geome y o i s bis-coo dina ion
complex, we discuss he p ope ies o he [N–I–N]
+
complexes 1-
I o 8-I in compa ison o he co esponding [N–Ag–N]
+
species 1-
Ag o 8-Ag (Fig. 1).
Syn hesis
[Bis(py idine)iodine]
+
e auo obo a e (1-I), pe chlo a e (2-I),
hexauo ophospha e (3-I), hexauo oan imona e (4-I), ia e
(5-I), osyla e (6-I), ni a e (7-I), and iuo oace a e (8-I)
complexes (Fig. 1), as well as hei selec i ely deu e a ed
analogues (1-I-d o 8-I-d), we e syn hesized ollowing a p e i-
ously published p ocedu e
30,46
om he co esponding
sil e (I) complexes (1-Ag o 8-Ag,1-Ag-d o 8-Ag-d). Complex
9was p epa ed by addi ion o 1.8 equi alen s o he anion
sca enge
47,48
dodecabenzylbambus[6]u il (Bn
12
BU[6]) o
he dichlo ome hane solu ion o 1-I, o p oduce a “naked”
[bis(py idine)iodine]
+
complex by apping he BF
4

coun e ion.
Fo he p epa a ion o [(1,2-bis(py idin-2-yle hynyl)benzene)
iodine]
+
e auo obo a e (10), ia e (11), and ni a e (12) and
hei mono-deu e a ed analogues (10-d o 12-d), published
syn he ic ou es
30
we e ollowed. See ESI† o de ails.
Coun e ion coo dina ion in solu ion
Ion coo dina ion in solu ion was e alua ed by acqui ing he
ansla ional diffusion coefficien o he posi i ely and nega-
i ely cha ged species o complexes 1–9(Table 1), using
1
H and
19
F NMR. Tigh anion coo dina ion o [bis(py idine)iodine]
+
was
indica ed by he compa able ansla ional diffusion a es o he
wo ions in he same solu ion, o each s udied sys em. A
signican diffe ence be ween he diffusion coefficien s o he
anionic and ca ionic species was de ec ed o 9-I. This indica es
ha [bis(py idine)iodine]
+
and BF
4

o 9-I do no o m a igh
ion pai . In line wi h ou expec a ions, he diffusion a e o he
apped BF
4

o 9-I is lowe han ha o 1-I, and ma ches he
diffusion a e o he anion sca enging agen Bn
12
BU[6] (D¼
5.8 10
10
m
2
s
1
) ha was added o he solu ion. The slowe
diffusion a e o [bis(py idine)iodine]
+
o 9-I han ha o 1-I is
well explained by he inc eased sol a ion o cha ged species as
compa ed o neu al ones in apola sol en s,
49
and by an
inc eased iscosi y o he solu ion upon addi ion o Bn
12
BU[6].
Diffusion NMR e eals s ong coo dina ion o he coun e ions
o he sil e cen e ed complexes 1-Ag o 8-Ag as well.
Fig. 1 The s uc u e o he model sys ems assessed o elucida ion o
he coun e ion (Y

)effec on he [N–I–N]
+
halogen bond (X ¼I):
[bis(py idine)iodine]
+
BF
4

(1-I), ClO
4

(2-I), PF
6

(3-I), SbF
6

(4-I),
T O

(5-I), TsO

(6-I), NO
3

(7-I), and CF
3
CO
2

(8-I), and hei
geome ically es ained [(1,2-bis(py idin-2-yle hynyl)benzene)
iodine]
+
BF
4

(10-I), T O

(11-I) and NO
3

(12-I) analogues. The BF
4

o 9-I was sca enged wi h dodecabenzylbambus[6]u il (Bn
12
BU[6]).
47
The spec oscopic da a o 1-I o 8-I we e compa ed o hose o he
co esponding sil e (I) complexes (X ¼Ag) 1-Ag o 8-Ag.
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15
N NMR is a sensi i e ool o in es iga ion o halogen bond
o ma ion,
30,43,45,50
and is commonly used o he assessmen o
sol en effec s, p o ona ion and me al coo dina ion o ni oge-
nous Lewis bases.
51–53
The
15
N NMR chemical shiso
compounds 1–9we e de ec ed using
1
H,
15
N-HMBC expe i-
men s,
54
p o iding a single signal o each compound (Table 1).
Fo ma ion o he [N–I–N]
+
complex is accompanied by a
compa able, la ge han 100 ppm chemical shichange
(py idine, d
15N
¼67 ppm ( e . 30)) o 1-I o 9-I. The a ia ion
o he
15
N NMR chemical shiso 1-Ag o 8-Ag indica es ha , in
con as o iodine(I), sil e (I) in e ac s wi h anions in a coo di-
na ion-s eng h dependen manne . Sol en and coun e ion
coo dina ion o sil e (I) complexes has p e iously been epo -
ed
52
o ha e a majo inuence on py idine
15
N NMR
coo dina ion shis(d
coo d
¼d
complex
d
ligand
). S ongly coo -
dina ing coun e ions may con e he linea , bis-
coo dina e [bis(py idine)sil e ]
+
o is-coo dina e, neu al
[bis(py idine)(coun e ion)sil e ] complexes.
52,55
The complex
8-Ag shows he mos deshielded
15
N NMR chemical shiamong
he sil e (I) complexes, which is in line wi h CF
3
CO
2

being he
s onges coo dina ing anion o he se ies. A smalle absolu e
coo dina ion shi,41–45 ppm, o he sil e (I) complexes pos-
sessing s ongly coo dina ing coun e ions, such as TsO

,
CF
3
CO
2

and NO
3

, is explained by an efficien cha ge ans e
om he anion o sil e (I) h ough o bi al o e lap. This
dec eases he posi i e cha ge o sil e (I) and consequen ly he
cha ge ans e om he py idine ni ogens o sil e (I), yielding
smalle
15
N NMR coo dina ion shis. The small, #1 ppm,
15
N
chemical shi a ia ion o 1-I o 9-I indica es he absence o an
analogous di ec cha ge ans e in e ac ion o he coun e ion
o he iodine(I) o [bis(py idine)iodine]
+
. Hence, s ong di ec
coo dina ion o a coun e ion o iodine(I) by o bi al o e lap does
no ake place; a he , his in e ac ion emains elec os a ic.
Sligh ly lowe
15
N NMR chemical shis we e obse ed o 10-I
(165.5 ppm), 11-I (165.0 ppm) and 12-I (163.3 ppm),
eec ing weakened N–I bonds, as a consequence o he s e ic
es ain in oduced by he 1,2-die hynylbenzene backbone.
28
The p opensi y o he coun e ions o 1-I o 9-I o compe e
wi h py idine o coo dina ion o he emp y p-o bi al o I
+
was
e alua ed by analyses o he
15
N NMR chemical shis o he
[bis(py idine)iodine]
+
coun e ion and o he al e na i e
[(py idine)(coun e ion)iodine] py idine geome ies, p edic ed a
he B3LYP le el using he dichlo ome hane con inuum sol en
model (Table 2, see ESI† o de ails). The
15
N chemical shiso
he [bis(py idine)iodine]
+
coun e ion geome ies o 1-I o 8-I
(N
B
, Table 2) a e p edic ed o be i ually coun e ion indepen-
den , and compa able in magni ude o hose expe imen ally
obse ed (Table 1). In con as , conside ably coun e ion depen-
den shis a e p edic ed o he [(py idine)(coun e ion)iodine]
complexes (N
A
, Table 2), wi h highe shielding o he ni ogen o
hose encompassing weake coo dina ing anions. This sugges s
ha py idine e sus anion exchange does no ake place.
Compu a ional he mochemical analysis p edic s ha o ma ion
o a [(py idine)(coun e ion)iodine] complex is endo he mic o
complexes ha possess weakly and mode a ely coo dina ing
anions, ye somewha exo he mic o TsO

,NO
3

,andCF
3
CO
2

(Table 2). I should be unde lined ha he applied he mochemical
calcula ion does no ake in o accoun he elec os a ic a ac ion
ha a ises in he elec oly e o med by [bis(py idine)iodine]
+
and
i s coun e ion in he solu ion. This a ac ion, which is also
supposed o accoun o he a ia ion in he expe imen al
15
N
shis o 1-I o 8-I,ises ima ed obe20–30 kJ mol
1
(see ESI†
o de ails). Wi h his co ec ion, he DFT esul s a e compa ible
wi h he [bis(py idine)iodine]
+
complex, being s able o 1-I o
Table 1 T ansla ional diffusion coefficien s, measu ed by
1
H and
19
F NMR de ec ion, and
15
N NMR chemical shi s
Anion S uc u e D(ca ion)
a
10
10
(m
2
s
1
)D(anion) 10
10
(m
2
s
1
)d(
15
N) (ppm)
BF
4

1-I 16.8 16.4 175.1
ClO
4

2-I 9.5 —
c
175.0
PF
6

3-I 10.3 10.5 175.8
SbF
6

4-I 9.8 —
d
175.1
T O

5-I 14.0 15.0 175.1
TsO

6-I 16.3 16.2 174.8
NO
3

7-I 10.8 —
c
174.8
CF
3
CO
2

8-I 18.7 15.7 175.2
[BF
4

]
b
9-I 9.4 6.0 175.5
BF
4

1-Ag 9.3 9.9 126.5
ClO
4

2-Ag 10.7 —
c
124.0
PF
6

3-Ag 9.5 9.4 128.4
SbF
6

4-Ag 15.1 —
d
129.3
T O

5-Ag 13.1 13.0 122.0
TsO

6-Ag 9.4 8.5 111.8
NO
3

7-Ag 10.4 —
c
113.1
CF
3
CO
2

8-Ag 15.2 12.9 109.5
a
[Bis(py idine)iodine]
+
.
b
BF
4

was sca enged wi h Bn
12
BU[6] in his solu ion p o iding a naked [bis(py idine)iodine]
+
.
c
This anion lacks an NMR
ac i e nucleus p e en ing he acquisi ion o i s diffusion coefficien .
d
The
19
F NMR signal o his coun e ion is ex ensi ely spli and b oadened due
o
1
J
Sb,F
.
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8-I. S ong ion pai ing is suppo ed by he diffusion NMR da a.
This conclusion is u he suppo ed by de ec ion o he
[bis(py idine)iodine]
+
complex by HR(ESI)MS o all s udied
sys ems (see ESI o de ails†), u he co obo a ing ha py idine
e sus anion exchange does no ake place in solu ion.
The
15
N NMR shio 9-I is compa able o ha o 1-I, sug-
ges ing ha he p esence o absence o a weakly coo dina ing
coun e ion does no inuence he elec on dis ibu ion o he
[N–I–N]
+
halogen bond. The BF
4

o 9-I was sca enged by
addi ion o an excess (1.8 eq.) o Bn
12
BU[6] o he solu ion o 1-I
wi h he efficien apping o he coun e ion being con med by
cha ac e is ic changes (a) in he
1
H NMR chemical shiso
bambusu il
47
(Fig. 2), (b) o he ansla ional diffusion coeffi-
cien s o BF
4

(Table 1), (c) o he
15
N NMR shis al e a ion o
Bn
12
BU[6] (Dd
15N
¼2.1 ppm o N–CH
3
,and2.4ppm o N–CH
2
,
Fig. S1†), and (d) by obse a ion o in e molecula
1
H,
19
Fhe e -
onuclea O e hause effec s be ween BF
4

and Bn
12
BU[6]
(Fig. S2†) whe eas he e is no
1
H,
1
H NOESY c osspeak be ween
[bis(py idine)iodine]
+
and Bn
12
BU[6]. The use o an excess o
Bn
12
BU[6] in he s udies o 9-I ensu ed he absence o ee BF
4

in
solu ion, and hence ha a coun e ion- ee [bis(py idine)iodine]
+
complex was in es iga ed. EXSY c osspeaks be ween he signals
o he ee and BF
4

-bound Bn
12
BU[6] (Fig. S3†) indica ed anion
mig a ion be ween he Bn
12
BU[6] uni s. Upon addi ion o Bn
12
BU
[6] o 8-I, he
15
N NMR chemical shi emained unal e ed,
suppo ing he abo e conclusions, and in addi ion u he
con med ha CF
3
CO
2

is incapable o compe ing wi h py idine
o iodine(I) coo dina ion.
Halogen bond symme y in solu ion
Iso opic pe u ba ion o equilib ium (IPE) NMR
56
is a echnique
capable o dis inguishing be ween a s a ic, symme ic geome y
and a apidly in e con e ing pai o asymme ic geome ies in
solu ion. I has been used success ully, o example, in he
symme y elucida ion o [N–H/N]
+
hyd ogen bonded
57,58
and
[N/X/N]
+
halogen bonded
30,46
molecula sys ems, as well as o
ca boca ions
59
and me al chela ing complexes.
60
The main
ad an age o IPE is ha i succeeds e en when he apidly
in e con e ing species canno be “ ozen ou ”due o a shallow
ene gy ba ie be ween hem. I equi es he analysis o an
iso opologue mix u e o a compound, which is oen a mix u e
o i s selec i ely deu e a ed and nondeu e a ed analogues. In
such solu ions, wo se s o NMR signals a e obse ed due o he
seconda y iso ope effec on he ib a ional equencies.
61
The
chemical shidiffe ence o he signal o igina ing om he
deu e a ed and ha o he nondeu e a ed molecule, mos
commonly de ec ed a
13
C NMR equency, is he seconda y
iso ope effec (IE) (eqn (1)),
n
D
obs
¼dC
(D)
dC
(H)
(1)
whe e nis he numbe o bonds be ween he deu e ium and he
obse ed nucleus, whils C
(D)
and C
(H)
a e he
13
C NMR chem-
ical shis o he deu e a ed and nondeu e a ed iso opologues.
Al hough he magni ude o he iso ope effec is dependen on
he dis ance o he de ec ed nucleus om he posi ion o
Table 2 Compu a ionally p edic ed
15
N NMR chemical shi s o he (A)
[(py idine)(coun e ion)iodine] py idine and o he al e na i e (B)
[bis(py idine)iodine(coun e ion)] geome ies o 1-I o 8-I, and he
es ima ed ene gies o (1) he hypo he ical eac ion o a py idine-
coun e ion exchange, and (2) he o ma ion o he [bis(py idine)iodi-
ne(coun e ion)] ion pai
a
Anion S uc u e
d(
15
N) ppm DGkJ mol
1
N
A
N
B
(1) (2)
BF
4

1-I 222.6 173.7 28.9 5.4
ClO
4

2-I 201.5 173.9 18.5 6.2
PF
6

3-I 233.6 174.3 44.2 19.7
SbF
6

4-I 233.9 174.6 39.7 3.9
T O

5-I 198.7 173.6 12.6 9.4
TsO

6-I 182.2 175.2 6.1 37.7
NO
3

7-I 180.3 172.7 16.4 4.9
CF
3
CO
2

8-I 176.1 173.2 25.7 40.4
a
The expe imen al
15
N NMR chemical shio 9-I was used as seconda y
e e ence.
Fig. 2 The alipha ic egion o he
1
H NMR o dodecabenzylbambus[6]
u il (Bn
12
BU[6]) in he absence and p esence o complex 1/1-d.Top ow
( ed): he spec um o ee Bn
12
BU[6]. Middle ow (g een): he spec um
ollowing addi ion o 1 eq. [bis(py idine)iodine]
+
e afluo obo a e o
he solu ion. The coun e ion is apped as [(Bn
12
BU[6])(BF
4

)]. Bo om
ow (blue): he spec um o Bn
12
BU[6] wi h 0.55 eq. [bis(py idine)iodine]
+
e afluo obo a e. Signals belonging o he BF
4

complexed and
he ee Bn
12
BU[6] a e obse ed simul aneously, indica ing s ong
BF
4

binding. Hence, he use o an excess o Bn
12
BU[6] ensu es
he comple e apping o he anion om he dichlo ome hane
solu ion.
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iso opic subs i u ion, a sizeable
n
D
eq.
need no be es ic ed o a
small n. The obse ed iso ope effec ,
n
D
obs
, consis s o in insic,
n
D
0
, and equilib ium,
n
D
eq.
, iso ope effec s (eqn (2)).
n
D
obs
¼
n
D
0
+
n
D
eq.
(2)
The  s componen ,
n
D
0
, is he di ec consequence o
iso ope subs i u ion, and is essen ially empe a u e indepen-
den . The second componen ,
n
D
eq.
, mani es s only in sys ems
ha a e in ol ed in a dynamic exchange p ocess. Due o i s
dependence on he equilib ium cons an o an exchange
p ocess (eqn (3)),
n
D
eq.
is empe a u e dependen .
n
D
eq.
¼D(K1)/[2(K+ 1)] (3)
whe e Kis he equilib ium cons an and Dis he chemical shi
diffe ence o he exchanging species, in his s udy he chemical
shidiffe ence o a selec ed nucleus in he N
d+
–I, and he
N
d
/I
d+
o ms o py idine. Acco dingly, s a ic ([N/I/N]
+
) and
dynamic ([N–I/N]
+
%[N/I–N]
+
) halogen bonding geome ies
a e dis inguishable in solu ion by obse a ion o he empe a-
u e dependence o hei
2
H-induced
13
C NMR iso ope
effec s.
30,56
We applied IPE o e alua e whe he he geome y o he h ee-
cen e [N–I–N]
+
halogen bond o [bis(py idine)iodine]
+
14,30,46
could be inuenced in solu ion by coun e ion coo dina ion.
P e iously his bond was demons a ed o be s a ic and
symme ic in solu ion in a complex encompassing T O

as
coun e ion.
30
By acquisi ion o
13
C{
1
H,
2
H} NMR spec a o
iso opologue mix u es o 1-I o 9-I dissol ed in CD
2
Cl
2
a a ious
empe a u es, he empe a u e dependence o he iso ope shis
was de e mined.
62
Simila o p e ious s udies,
30,45,46,63
he C3
posi ion o he py idine o 1-I o 9-I showed he la ges
empe a u e dependence and p o ided da a wi h he highes
squa ed co ela ion coefficien s (Fig. 3). The o e all smalle
empe a u e dependence o he IEs o he s udied [bis(py idine)
iodine]
+
complexes (Table 3) as compa ed o ha o py idine
py idinium ia e (5-H), which was p e iously shown o exis as
a apidly in e con e ing au ome ic mix u e,
30,45,46
indica es
ha 1-I o 9-I a e p esen as s a ic, symme ic species in solu ion.
He e i should be no ed ha he nonze o empe a u e depen-
dence o he in insic iso ope effec s is due o he empe a u e
dependence o he pola i y o he sol en ,
64
he pola i y-al e -
a ion o he sol en modula es he cha ge dis ibu ion o py i-
dine.
65
An efficien elec on densi y ans e be ween he
ni ogen lone pai and adjacen bonds, inuencing he magni-
ude o he obse ed iso ope effec s as well as he amine basici y,
has been p e iously desc ibed.
66
Th ough-space pola iza ion ia
dipola in e ac ion has also been epo ed p e iously o e he s,
o example.
67
The s a ic symme ic [N/I/N]
+
geome y o 1-I
o 9-I is co obo a ed by he p ima y dependency o he
magni ude o hei IEs on he dis ance o he obse ed ca bon
om he posi ion o
1
H- o-
2
H subs i u ion, in con as o hose
o [bis(py idine)hyd ogen]
+
ia e 5-H (Table 3) being
p edominan ly dependen on he numbe o in e ening bonds
be ween he obse ed nucleus and he ni ogen in ol ed in o he
[N–H/N]
+
%[N/H–N]
+
au ome iza ion p ocess.
31,68
Simila o
1-I,9-I has a s a ic, symme ic [N/I/N]
+
halogen bond in
solu ion, con ming ha a weakly coo dina ing anion does no
inuence he symme y o he iodine cen e ed halogen bond.
The abo e obse a ions ag ee wi h he p e iously epo -
ed
15,30,43,46
high ene ge ic gain upon o ma ion o a symme ic
[N/I/N]
+
halogen bond. Simila o o he s,
13
we ha e obse ed
a lowe s abili y o 5-I, mani es ed in i s sho e li e ime in
solu ion as compa ed o [bis(py idine)iodine]
+
complexes ha
encompass o he coun e ions. This diffe ence is likely due o he
hyg oscopici y o iic acid and no due o any specic in e -
ac ion o T O

wi h he [N/I/N]
+
halogen bond. Coun e ion
dependen s abili y and eac i i y o [bis(py idine)halogen]
+
Fig. 3 The simila empe a u e dependence o he wo-bond iso ope
effec (
2
D
obs
) measu ed on C-3 o 1-I o 8-I indica es ha he [N–I–N]
+
halogen bond is s a ic and symme ic in solu ion, ega dless o he
coun e ion. BBF
4

,;ClO
4

,-PF
6

,,SbF
6

,CT O

,ATsO

,O
NO
3

,:CF
3
CO
2

, and >BF
4

.
Table 3 Tempe a u e coefficien s (ppm K) o he iso ope shi s o 1–9,
obse ed o CD
2
Cl
2
solu ions
Anion S uc u e C2
1
D
obs
C3
2
D
obs
C4
3
D
obs
C5
4
D
obs
C6
3
D
obs
BF
4

1-I 6.6 8.4 0.3 0 2.9
ClO
4

2-I 5.6 8.3 0.3 0 3.6
PF
6

3-I 6.3 8.9 0.4 0 3.4
SbF
6

4-I 6.2 9.0 0.8 0 3.4
T O

5-I 5.9 8.5 0.2 0 3.8
T O

5-H
b
6.1 9.8 4.5 5.8 6.5
TsO

6-I 2.6 8.1 0.3 0 3.2
NO
3

7-I 5.8 8.0 0.9 0 2.5
CF
3
CO
2

8-I 6.3 8.8 0.9 0 4.6
[BF
4

]9-I
a
6.5 9.4 0.6 0 3.5
BF
4

10-I 6.5 9.4 n.d.
c
0 n.d.
c
T O

11-I
b
7.4 6.5 2.4 0 2.7
T O

11-H
b
10.0 10.6 3.5 0 +15.0
NO
3

12-I n.d.
c
9.8 2.5 0 4.2
a
The coun e ion o 9-I was sca enged using Bn
12
BU[6] p o iding a
naked [bis(py idine)iodine]
+
.
47
b
The da a o 5-H,11-I and 11-H a e
om e . 30 and 46.
c
Due o limi ed solubili y and mino
empe a u e dependence, his coefficien could no be eliably
de e mined.
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complexes may inuence hei syn he ic applicabili y,
36,41,69
encou aging o u he s udies.
The h ee-cen e halogen bond is sligh ly des abilized by he
in oduc ion o a geome ical es ain en o cing a somewha
longe han op imal ni ogen–ni ogen dis ance o he [N/I/N]
+
bond, he eby dec easing he o e lap o he lled nonbonding
o bi al o he py idine ni ogens wi h he emp y p-o bi al o iodi-
ne(I).
30,45
Consequen ly, op imal N–I bond leng hs a e ob ainable
o such a sys em only upon an ene ge ically penalized adjus men
o i s co alen backbone. To e alua e whe he he coun e ion is
capable o inuencing a weakened h ee-cen e halogen bond,
[(1,2-bis(py idin-2-yle hynyl)benzene)iodine]
+
complexes (Fig. 1)
encompassing he weakly coo dina ing e auo obo a e (10-I),
he mode a ely coo dina ing ia e (11-I), and he s ongly coo -
dina ing ni a e (12-I) we e assessed using IPE NMR. The o e all
lowe empe a u e dependence o he IEs o 10-I o 12-I as
compa ed o 11-H (Table 3), and he p ima y dependence o he
empe a u e coefficien s o hei IEs on he posi ion o he
1
H- o-
2
H subs i u ion indica e ha he [N/I/N]
+
halogen bond
o hesesys emsisalsos a icandsymme ic.Hence,coun e ion
coo dina ion is incapable o in oducing asymme y in o e en a
sligh ly weakened h ee-cen e halogen bond in solu ion.
Coun e ion coo dina ion in silico
Fo heo e ical con ma ion o he expe imen al ndings, he
equilib ium geome ies o 1-I o 9-I we e calcula ed using
densi y unc ional heo y (DFT) employing he B3LYP exchange
and co ela ion unc ional.
70–73
In he he mochemical calcula-
ions, he LANL08d and LANL08
74
basis se s, in conjunc ion
wi h he LANL2DZ
75,76
effec i e co e po en ial, we e used o I
and Sb, espec i ely; he LANL2DZ
75,76
basis se was used o Ag;
Pople's 6-311+G(d,p)
77–79
basis se was used o B, O, N, F and Cl;
and Pople's 6-311G(d,p) basis se was used o he emaining
a oms. Fo he es ima ion o chemical shieldings, single-poin
calcula ions a he geome ies ob ained we e pe o med using
he 6-311+G(d,p) basis se
80
o I, and Ku zelnigg's IGLO-III
basis se
81
o he emaining a oms. Sol en effec s we e
accoun ed o by he Pola izable Con inuum Model (PCM),
82,83
wi h CH
2
Cl
2
as he sol en . All calcula ions we e pe o med
using he Gaussian09 p og am package.
84
The po en ial ene gy
su aces (PES) o all he complexes con aining coun e ions a e
complica ed and likely o show a numbe o local minima o
he placemen and o ien a ion o he coun e ion. Ca e was
aken o nd he mos a ou able congu a ion o each coun-
e ion; howe e , i can ne e be ully excluded ha he e a e
local minima wi h sligh ly lowe ene gies han hose p esen ed.
The PESs a e shallow in he egion o in e es , so e en i a
sligh ly lowe minimum geome y was missed his would no
affec he conclusions o he he mochemical analysis, shown in
Table 2. In good ag eemen wi h he spec oscopic da a, DFT
calcula ions p edic symme ic [bis(py idine)iodine]
+
geome y
o complexes 1-I o 9-I. The mino , <0.2%, diffe ence in he N–I
bond leng hs o 8-I (Table 4), o example, is likely insigni-
can .
85
The N–I bond leng h is i ually unaffec ed by he
coun e ion, whe eas he N–I–N angle shows some mino a i-
a ion, ye emains o e all linea . The la e de ia ion om
comple e linea i y is likely due o weak hyd ogen bonding o
some o he coun e ions o he H-2 o he py idines. This
in e ac ion has p e iously been no iced o s uc u ally closely
ela ed complexes.
52,86,87
Mos o he analogous sil e complexes
a e also linea and symme ic; howe e , a sligh asymme y
along wi h a signican dis o ion om linea i y o he N–Ag–N
angle is p edic ed o 5-Ag,7-Ag and 8-Ag. These complexes
encompass small, mode a ely o s ongly coo dina ing coun-
e ions (T O

,NO
3

and CF
3
CO
2

), and hei geome y is likely
al e ed due o he s e ic equi emen s o igh coun e ion
coo dina ion ha yields neu al, T-shaped and sligh ly asym-
me ic species (Fig. 4). Nei he small symme ic (BF
4

, ClO
4

,
PF
6

, SbF
6

) no la ge s e ically hinde ed anions (TsO

) a e
capable o di ec coo dina ion o sil e (I) in hese complexes. I
should be no ed ha he co esponding iodine(I) cen e ed
complexes 7-I and 8-I do no o m a compa able s ong iodine–
oxygen bond, and hus emain linea and bis-coo dina e.
Coun e ion coo dina ion in he solid-s a e
Single c ys als we e ob ained ia slow diffusion o hexane in o he
dichlo oe hane solu ion o he s udied complexes unde s epwise
cooling om 25 C o20 C. X- ay c ys allog aphic analyses
e ied ha he iodine cen e ed complexes 1-I o 7-I p e e a
symme ic, linea , bis-coo dina ed N–I–N s uc u e in he solid
s a e (Table 4). The coun e ion has only a mino , <2%, inuence
on he N–I bond leng hs. A weak coo dina ion o he anions and
hei consequen negligible effec on he geome y o he h ee-
cen e ed halogen bond in he solid s a e is in good ag eemen
wi h he DFT p edic ed s able, symme ic [bis(py idine)iodine]
+
solu ion geome ies. The N–I bond leng hs o hese complexes
a e signican ly sho e han he sum o he an de Waals adii
o he pa icipa ing a oms (R
XB
¼0.64, whe e R
XB
¼d
NI
/(I
dW
+
N
dW
)
88
), well eec ing he unusual s eng h o he halogen
bond
29
o 1-I o 7-I. Impo an ly, he asymme ic coo dina ion o
he coun e ion (Fig. 5) o hese complexes is unable o induce
asymme y in he h ee-cen e halogen bond. Whe eas
he [N/I/N]
+
in e ac ion has a signican co alen
cha ac e ,
15,28,30,43,45
he coo dina ion o he coun e ions o
[bis(py idine)iodine]
+
is p edominan ly Coulombic and is weak.
Un o una ely, single c ys als o complex 8-I we e no ob ained,
despi e epea ed a emp s.
Sil e (I) cen e ed complexes 1-Ag o 4-Ag ha encompass
weakly coo dina ing anions p e e linea , bis-coo dina e N–Ag–
N geome ies in he solid s a e (Table 4). The in e ac ion o
[bis(py idine)sil e ]
+
wi h hese coun e ions is o ionic cha -
ac e , simila o ha o he co esponding [bis(py idine)
iodine]
+
. In con as , pseudo- e acoo dina e (3 + 1) dime s we e
obse ed o 5-Ag and 6-Ag ha possess he mode a ely coo -
dina ing coun e ions T O

and TsO

(Fig. 5). X- ay analyses o
[bis(py idine)sil e ]
+
ni a e showed a pseudo-squa e plana N–
Ag(NO
3

)
2
–N geome y (Fig. 6a, Table 4, 7-Ag), and a e ame
(dime o dime s) wi h an ex ao dina y combina ion o a
pseudo- e ahed al (2 + 2) N–(Ag)Ag(NO
3

)–N coo dina ion and
an excep ional pseudo-oc ahed al (5 + 1) N–(Ag)Ag(NO
3

)
2
–N
coo dina ion (Fig. 6b, Table 4, 7-Ag-2). Despi e epea ed
a emp s, single c ys als o he [bis(py idine)sil e ]
+
complex
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wi h he s ongly coo dina ing coun e ion CF
3
CO
2

(8-Ag) we e
no ob ained. X- ay analyses o 7-Ag and 8-Ag we e a emp ed
ea lie by Whi e e al.,
90
who epo ed he o ma ion o binuclea
species con aining sil e ni a e and py idine in a 1 : 3, and
sil e iuo oace a e and py idine in a 3 : 2, a io. DFT p edic s
he is-coo dina e complexes o 7-Ag and 8-Ag o be ene ge i-
cally mo e a o able han hei bis-coo dina e analogues. The
s ong in e ac ion o he coun e ion o complexes 5-Ag o 8-Ag
wi h sil e (I) mani es s in specic, close in e a omic con ac s,
i.e. d
Ag–O
¼2.705 ˚
A(5-Ag, XRD), 2.545 ˚
A(6-Ag, XRD), 2.690 ˚
A(7-
Ag, DFT), and 2.749 ˚
A(8-Ag, DFT). The coun e ion coo dina ion
o sil e (I) in hese species is s ong (R
coo d
¼0.79–0.85, whe e
Table 4 Compu a ionally p edic ed and X- ay c ys allog aphically de e mined N–X bond dis ances and N–X–N bond angles o he complexes
1-I o 9-I and 1-Ag o 8-Ag
Anion S uc u e
Compu a ionally p edic ed dis ances and angles X- ay c ys allog aphic dis ances and angles
(N–X)
1
(˚
A) (N–X)
2
(˚
A) s(N–X–N) () (N–X)
1
(˚
A) (N–X)
2
(˚
A) s(N–X–N) ()
BF
4

1-I
a
2.301 2.301 178.0 2.260(3) 2
c
180.0
2.261(3) 2
c
180.0
2.255(3) 2.261(3) 177.7(1)
ClO
4

2-I 2.301 2.301 175.8 2.257(2) 2
c
180.0
2.260(2) 2
c
180.0
2.256(2) 2.256(2) 177.72(9)
PF
6

3-I 2.303 2.301 178.8 2.268(2) 2.268(2) 180.0
SbF
6

4-I 2.302 2.302 179.2 2.252(3) 2.252(3) 180.0
T O

5-I 2.301 2.300 178.0 2.246(8) 2.261(7) 178.0(3)
TsO

6-I 2.301 2.300 177.8 2.241(3) 2.268(3) 178.75(8)
NO
3

7-I 2.303 2.303 179.0 2.250(4) 2
c
180.0
2.265(3) 2
c
180.0
CF
3
CO
2

8-I 2.302 2.298 177.4 ———
[BF
4

]9-I
b
2.301 2.301 180.0 ———
BF
4

1-Ag 2.198 2.197 175.7 2.137(3) 2.138(3) 176.0(1)
ClO
4

2-Ag 2.190 2.189 179.1 2.131(3) 2.132(3) 177.0(1)
PF
6

3-Ag 2.193 2.192 176.9 2.128(4) 2.133(4) 176.9(1)
SbF
6

4-Ag 2.193 2.192 178.0 2.130(2) 2.143(2) 174.84(8)
T O

5-Ag 2.225 2.222 166.8 2.153(4) 2.158(3) 167.4(1)
TsO

6-Ag 2.191 2.188 176.8 2.177(2) 2.192(2) 155.01(7)
NO
3

7-Ag 2.251 2.251 162.5 2.176(2) 2.176(2) 173.85(8)
NO
3

7-Ag-2 2.152(2) 2.152(2) 173.2(1)
2.255(3)
d
——
CF
3
CO
2

8-Ag 2.274 2.250 164.5 ———
a
C ys allog aphic da a is om e . 89.
b
Compu a ional da a is om e . 30.
c
Complex lies on a symme y elemen wi h wo equal N–I dis ances
wi h an exac 180angle.
d
Only one Ag–N bond in a pseudo-oc ahed al complex.
Fig. 4 The DFT-p edic ed equilib ium geome ies o complexes 8-Ag
and 8-I a e shown on he le and igh , espec i ely. Whe eas sil e (I)is
p edic ed o o m T-shaped, is-coo dina e species wi h a s ongly
bound coun e ion, sho iodine–oxygen con ac is no seen o he
co esponding iodine(I) complex, which p e e s a linea , bis-coo di-
na e N–I–N geome y.
Fig. 5 The solid s a e geome ies o complexes (a) 5-Ag, (b) 6-Ag, (c)
5-I and (d) 6-I ob ained by X- ay c ys allog aphy e eal ha he
bis(py idine) complexes o sil e (I) o m pseudo- e acoo dina ed
dime s, whe eas hose o iodine(I) o m ionic, linea , bis-coo dina ed
N–I–N complexes in he p esence o mode a ely coo dina ing
coun e ions, such as T O

and TsO

.
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R
coo d
¼d
Ag–O
/(Ag
dW
+O
dW
)
29,88
), ye i emains weake as
compa ed o he coo dina ion o py idines (R
coo d
¼0.67–0.69).
[(1,2-Bis(py idin-2-yle hynyl)benzene)sil e ]
+
ni a e (12-Ag)
c ys allized as a T-shaped complex, as shown in Fig. 7. The N–Ag
bond dis ances o 2.169(3) ˚
A and 2.177(3) ˚
A, and he Ag–O bond
dis ance o 2.658(4) ˚
A o his complex co espond well o hose
obse ed o he s e ically un es ained 7-Ag (Table 4). The
adap abili y o he (1,2-bis(py idin-2-yle hynyl)benzene) back-
bone o his complex o pe mi op imal ni ogen–ni ogen
dis ances o complexa ion ag ees well wi h p e ious obse a-
ions made o he analogous [N/I/N]
+
and [N/B /N]
+
complexes.
30
Conclusions
Coun e ions do no inuence he in insically p e e ed linea ,
cen osymme ic geome y o he [N/I/N]
+
halogen bond,
ei he in solu ion o in he solid s a e. Nei he does he sca -
enging o he coun e ion inuence he symme y o he h ee-
cen e bond. In con as , he weakly coo dina ing coun e ions
BF
4

and ClO
4

we e p oposed
34,35
o be capable o desymme-
izing he [N/B /N]
+
halogen bond o [bis(py idine)b omine]
+
in he solid s a e. This obse a ion may be explained by he
lowe ene gy gain upon o ma ion o he [N/B /N]
+
as
compa ed o he [N/I/N]
+
halogen bond.
43
The h ee-cen e
halogen bonds o 1-I o 8-I esemble he classical coo dina ion
bond o he co esponding [N/Ag/N]
+
complexes.
28
Whe eas
mode a ely and s ongly coo dina ing coun e ions, e.g. T O

,
TsO

,NO
3

and CF
3
CO
2

, do no affec he [N/I/N]
+
halogen
bond, hey ha e a conside able inuence on he co esponding
coo dina i e sil e (I) complexes. Hence, he la e a e al e ed
om linea , bis-coo dina e [bis(py idine)sil e ]
+
coun e ion
complexes o mul i-coo dina e [bis(py idine)(coun e ion)sil e ]
species. These coun e ions en o ce nonlinea , and occasionally
also asymme ic geome ies, o he [N/Ag/N]
+
coo dina ion
bonds. This is mos appa en in he solid s a e (Table 4, Fig. 5
and 6), and ye i akes place in solu ion (Fig. 4) as well.
O e all, he h ee-cen e [N/I/N]
+
and [N/Ag/N]
+
bonds
beha e simila ly in he p esence o weakly coo dina ing anions
(1-I o 4-I, and 1-Ag o 4-Ag), bu diffe en ly when mode a ely o
s ongly coo dina ing coun e ions a e p esen (5-I o 8-I, and 5-
Ag o 8-Ag). Ou esul s sugges ha ca e should be aken when
he h ee-cen e halogen bond is discussed in e ms o coo di-
na ion bonds o ansi ion me als. The [N/I/N]
+
bonds a e
bes desc ibed as halogen bonds possessing a signican cha ge
ans e cha ac e ,
43
which is p esen o all ypes o halogen
bonds bu ye may be o a ying impo ance.
91–93
Despi e some
diffe ences,
15
he h ee-cen e [D/X/D]
+
halogen bond
esembles a “sho -s ong”[D/H/D]
+
hyd ogen bond,
94
and
may al e na i ely be e med a sho , s ong halogen bond.
[Bis(py idine)iodine]
+
complexes a e common syn he ic
eagen s o halogena ion and oxida ion,
95–103
wi h Ba luenga's
eagen being he mos amous one.
36,41
The la e was ecen ly
shown o exhibi a coun e ion dependen o de –diso de phase
ansi ion in he solid s a e
13
and has ecei ed inc easing
a en ion o applica ions in pa allel syn hesis
104
and p o ein
chemis y,
69
o example. The unde s anding o he s uc u e
and p ope ies o hese eagen s is he e o e o bo h unda-
men al and p ac ical impo ance.
Acknowledgemen s
The esea ch leading o hese esul s has ecei ed unding om
he Eu opean Union Se en h F amewo k P og amme (FP7/
2007–2013) unde g an ag eemen no. 259638. We hank he
Swedish Resea ch Council (2012:3819), he Academy o Finland
(263256 and 265328), and he Czech Science Founda ion (13-
15576S) o nancial suppo . FT acknowledges he suppo
om NGS-NANO h ough a Ph.D. ellowship. We hank Albe e
X. Veiga (Uni e si y o Go henbu g) o help ul syn he ic ad ice.
Molecula g aphics we e gene a ed wi h he UCSF Chime a
package,
82
by he Resou ce o Biocompu ing, Visualiza ion, and
In o ma ics a he Uni e si y o Cali o nia, San F ancisco (sup-
po ed by NIGMS P41-GM103311).
No es and e e ences
1 S. Gup a, D. Koley, K. Ra ikuma and B. Kundu, J. O g.
Chem., 2013, 78, 8624.
2 S. L. Dabb, J. H. Ho, R. Hodgson, B. A. Messe le and
J. Wagle , Dal on T ans., 2009, 634.
3 Y. Ren, X. Wang, S. Y. Chu and N. B. Wong, Theo . Chem.
Acc., 2008, 119, 407.
4 A. Eb ahimi, M. Habibi and A. Ami mijani, J. Mol. S uc .,
2007, 809, 115.
Fig. 6 X- ay c ys allog aphic in es iga ion o [bis(py idine)iodine]
ni a e e ealed (a) pseudo-squa e plana N–Ag(NO
3

)
2
–N(7-Ag), and
(b) coexis ing pseudo- e ahed al and pseudo-oc ahed al (5 + 1) N–
(Ag)Ag(NO
3

)
2
–N(7-Ag-2) coo dina ion geome ies.
Fig. 7 The X- ay s uc u e o 12-Ag.
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