Structural heterogeneity of AgI complexes with a flexible 1,2-bis[(imidazol-2-yl)thiomethyl]benzene ligand and issues regarding the phase purity of the bulk material

Article abstract of DOI:10.1002/ejic.201100853

A series of Ag^I coordination compounds with a new ligand, 1,2-bis[(imidazol-2-yl)thiomethyl]benzene, and counterions such as PF ₆^-, SbF₆^-, CF₃SO ₃^-, BF₄^- and NO₃ ^- was characterised by powder and single-crystal XRD. Powder XRD revealed the presence of a mixture of crystallographic phases that were further identified by single-crystal XRD. Despite conformational flexibility, 1,2-bis[(imidazol-2-yl)thiomethyl]benzene has a tendency to form N,N-chelated Ag^I mononuclear cationic complexes with a linear N-Ag^I-N unit. However, T-shaped geometry (N₂O) around the silver ion was also observed, which involved solvent molecules and/or counterions. The formation of a cationic 1D chain with the N,N′-bridging ligand was revealed with the BF₄^- counterion. Coordination compounds that possess different nuclearity were formed with the NO₃^- counterion. In the dinuclear and trinuclear complexes, the ligand showed bischelating behaviour with N-donor atoms that interact with one and S-donor atoms with another metal centre. Furthermore, the crystal structure of the trinuclear complex revealed the presence of two crystallographically independent cationic moieties in the asymmetric unit, which only differ by a single O-donor ligand (NO₃^- vs. H₂O), where both of the moieties possess three different geometries around the constituent silver ions. Argentophilic interactions are present in the majority of the reported structures. Available amine N atoms facilitate hydrogen bond formation and promote the occurrence of solvates. An XRD structural study of a series of Ag^I coordination compounds with a new flexible ligand, 1,2-bis[(imidazol-2-yl)thiomethyl]benzene, and counterions such as PF ₆^-, SbF₆^-, CF₃SO ₃^-, BF₄^- and NO₃ ^- prepared in MeOH in a 1:1 metal/ligand ratio, reveals vast structural diversity and highlights the difficulties of solid-state characterisation of bulk materials. Copyright

Full text of DOI:10.1002/ejic.201100853

FULL PAPER
DOI: 10.1002/ejic.201100853
Structural Heterogeneity of AgI Complexes with a Flexible 1,2-Bis[(imidazol-
2-yl)thiomethyl]benzene Ligand and Issues Regarding the Phase Purity of the
Bulk Material
Liliana Dobrzan´ska*[a,b]
Keywords: Silver / Ligand flexibility / Coordination modes / Phase purity / X-ray diffraction
A series of AgI coordination compounds with a new ligand,
1,2-bis[(imidazol-2-yl)thiomethyl]benzene, and counterions
dination compounds that possess different nuclearity were
formed with the NO3– counterion. In the dinuclear and trinu-
–
–
such as PF6–, SbF6–, CF3SO3–, BF4 and NO3 was character- clear complexes, the ligand showed bischelating behaviour
ised by powder and single-crystal XRD. Powder XRD re-
vealed the presence of a mixture of crystallographic phases
that were further identified by single-crystal XRD. Despite
conformational flexibility, 1,2-bis[(imidazol-2-yl)thiomethyl]-
benzene has a tendency to form N,N-chelated AgI mono-
nuclear cationic complexes with a linear N–AgI–N unit. How-
ever, T-shaped geometry (N2O) around the silver ion was also
observed, which involved solvent molecules and/or counter-
ions. The formation of a cationic 1D chain with the N,NЈ-
bridging ligand was revealed with the BF4– counterion. Coor-
with N-donor atoms that interact with one and S-donor atoms
with another metal centre. Furthermore, the crystal structure
of the trinuclear complex revealed the presence of two crys-
tallographically independent cationic moieties in the asym-
metric unit, which only differ by a single O-donor ligand
(NO3– vs. H2O), where both of the moieties possess three dif-
ferent geometries around the constituent silver ions. Ar-
gentophilic interactions are present in the majority of the re-
ported structures. Available amine N atoms facilitate hydro-
gen bond formation and promote the occurrence of solvates.
ever, the ortho-position of the thioimidazole substituents on
the benzene ring provides some rigidity in L. Previously re-
ported AgI complexes with a similar ligand, 1,2-bis(2-meth-
ylimidazol-1-ylmethyl)benzene (with 2-methylimidazole
rings in the ortho-position), revealed the formation of 1D
chains with PF6 , SbF6 and BF4 counterions in a metal/
ligand ratio of 1:1 as the 2-methyl groups successfully
prevent the formation of mononuclear species.[8] As will be
discussed further, elongation of the linker by the incorpora-
tion of an S-donor atom and, even more importantly, the
presence of a free NH in the imidazole ring, make the pre-
diction of the final products more complicated.
Introduction
During the last three decades, coordination chemistry
has increasingly been involved with more elaborate ligands
and studies of metal–organic complexes with extended
structures of different topologies.[1] This led to the discovery
of new, interesting properties connected with porosity, chi-
rality, magnetism and nonlinear optics, as well as the emer-
gence of related applications for these materials.[2] Imid-
azole-based ligands have been investigated for many years.
Initially, complexes with simple imidazole rings were
studied with focus on detailed spectroscopic and structural
characteristics.[3] When interest shifted to more complicated
linkers, the incorporation of imidazole rings was justified
by their reputation as effective N-donor building blocks.[4]
In continuation of our studies on imidazole-based ex-
tended linkers,[5] an investigation of the coordination chem-
istry of AgI complexes with a new ligand, 1,2-bis[(imidazol-
2-yl)thiomethyl]benzene (L, Scheme 1), was undertaken.[6]
L is more flexible than ligands that we have previously
studied due to the presence of a thioether linkage.[7] How-
–
–
–
Scheme 1. 1,2-Bis[(imidazol-2-yl)thiomethyl]benzene (L).
[a] Department of Chemistry, Katholieke Universiteit Leuven,
Celestijnenlaan 200F, 3001 Heverlee, Belgium
Fax: +32-16-327-990
E-mail: lianger@chem.kuleuven.be
Results and Discussion
[b] Department of Chemistry and Polymer Science, Stellenbosch
University,
All metal complexes were prepared similarly in a dark
environment with an Ag/L ratio of 1:1 (0.2:0.2 mmol). A
solution of silver salt (AgPF6 for 1, AgSbF6 for 2,
Private Bag X1, Matieland 7602, South Africa
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/jic.201100853
Eur. J. Inorg. Chem. 2012, 945–953
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945

L. Dobrzan´ska
FULL PAPER
AgCF3SO3 for 3, AgBF4 for 4 and AgNO3 for 5) in MeOH
(15 mL) was added to a solution of L in MeOH (25 mL).
The mixture was stirred for a few minutes and the resulting
clear solution was left to stand for ca. four weeks until crys-
talline material formed. Single crystals of 1–5 were isolated
from each vial and XRD measurements were performed to
reveal the presence of [AgL]PF6·CH3OH (1a) in 1, [AgL]-
SbF6 (2a) in 2, [AgL]CF3SO3·H2O (3a) in 3, {[AgL]BF4}n
(4a) in 4 and [Ag2L(NO3)2] (5a) in 5.
Powder XRD Studies
Figure 1. Asymmetric unit of 1a with displacement ellipsoids drawn
at the 50% probability level and hydrogen bonding shown in red
and blue.
Powder XRD (XRPD) analyses were performed to assess
the purity of the phases obtained.[9a] As there was no agree-
ment between the powder patterns generated from the sin-
gle-crystal structures (labelled as a) and the measured pow-
der patterns of the corresponding bulk material (Support-
ing Information, Figures S1–S5),[9b] a further study was
performed to identify the remaining crystallographic
phases. This way, new crystal structures were revealed
(Table S1). PowderCell 2.4 freeware was used to further esti-
mate the percentage of the respective crystallographic
phases (Figures S6–S9).[9c] It is not certain that all the
phases were identified, but the results seem to indicate that
at the time of the XRPD measurement, the respective com-
positions were as follows. Complex 1b, which contains
water molecules in the crystal lattice, was the major compo-
nent of 1 (more than 50%). Complex 2b, which also con-
tains water molecules, was the dominant phase in 2 (over
80%). In 4, mononuclear 4b was the major constituent (ca.
80%) over polynuclear complex 4a. Complexes 5c and 5a,
which show bischelating behaviour and have coordinated
nitrate ions, were the preferred phases in 5, and the presence
of mononuclear, cationic 5b was negligible.
the results below; see also Table 4)[10] supported by weak
interactions between imidazole rings from corresponding
mononuclear complexes with a centroid–centroid distance
of 3.507(2) Å (symmetry operation: –x, 1 – y, –z). Looking
down the b axis, columns of dimeric cationic complexes
stacked above each other are observed. These interact fur-
ther by C5–H5···S6#4 interactions [C5···S6 3.396(4) Å, for
symmetry operations, see Table S2]. The dimeric units ex-
pand along the c axis and are further held together by C–
H···π interactions between C10–H10···Cg1#6 [where Cg1 is
the centroid of the benzene ring belonging to the dimeric
unit from a neighbouring column; C10···Cg1 3.545(4) Å] to
form layers. These layers are separated by rows of alternat-
ing pairs of solvent molecules and counterions (Figure 2).
Weak N–H···F and C–H···F interactions support the pack-
ing (Table S2).
Single-Crystal XRD Studies
–
Crystal Structures of 1a, 1b, 1c and 1d Formed with PF6
(Bulk Material 1)
[AgL]PF6·CH3OH (1a)
Complex 1a crystallises in the monoclinic space group
P21/c and contains one mononuclear cationic AgI complex,
–
one PF6 counterion and one molecule of methanol in the
asymmetric unit (Figure 1). The silver atom in the complex
is linearly coordinated by the two imine N atoms that origi-
nate from the chelating imidazole rings of the ligand (for
bond lengths, see Table 2). The ligand adopts a folded con-
formation (Table 3) with a dihedral angle of ca. 34° between
the planes of the imidazole rings and the benzene ring. The
methanol molecule interacts with the amine N atom of the
cationic unit and the counterion by hydrogen bonding.
Figure 2. Representation of the packing of 1a viewed down the b
axis.
[AgL]PF6·H2O (1b)
The unit cell parameters of the crystal structure of 1b are
The solvent molecule acts as a hydrogen bond acceptor very similar to those of 1a, as are the main structural fea-
and donor simultaneously (Table S2). The distance between tures of the compound (the same type of coordination
neighbouring Ag ions indicates the presence of very weak sphere around the metal atom in the monomeric cationic
interactions between the Ag centres from nearby mononu- complex). A water molecule takes more or less the same
clear units (this conclusion was drawn by comparison with space that was previously occupied by the methanol mole-
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Eur. J. Inorg. Chem. 2012, 945–953

AgI Complexes with a Flexible Ligand
cule but it is badly disordered and modelled in four posi- [AgL]PF6·xCH3OH·xH2O (1c)
tions. An interaction between the water molecule and the
Complex 1c crystallises in the monoclinic space group
counterions is suspected but is not confirmed due to the
disorder present. The smaller size of solvent molecules
causes the neighbouring mononuclear cationic complexes
to pack closer, which shortens the distance between the sil-
ver ions (Table 4). This is also noticeable by a minor de-
crease of the length of the c axis (Table 1). Negligible
changes can also be seen in the position of the counterions.
C2/c with unit cell parameters different from those of 1a/1b
but very close to those obtained for 2b (Table S1). Unfortu-
nately, the quality of the crystals was too poor to fully char-
acterise the compound.
[AgLCH3O(H)0.5](PF6)0.5 (1d)
Complex 1d crystallises in the same monoclinic space
The water molecule shows interactions with the amine N group P21/c as 1a and 1b, but the unit cell parameters, the
atom. It might also interact with the counterions, but the conformation of the ligand and the packing are completely
disorder present renders it impossible to make any further different. It consists of one mononuclear cationic unit,
–
assumptions.
[AgLCH3O(H)0.5], and half a PF6 ion (the P atom is lo-
Table 1. Crystal data and details of the refinement parameters for the crystal structures originating from crystalline bulk material 1–5.
1a
1b
1d
2a
2b
Formula
Formula weight
Crystal system
Space group
T [K]
C15H18AgF6N4OPS2 C14H16AgF6N4OPS2 C30H35Ag2F6N8O2PS4 C14H14AgF6N4S2Sb
C28H34Ag2F12N8O3S4Sb2
1346.11
monoclinic
C2/c
587.29
monoclinic
P21/c
573.27
monoclinic
P21/c
1028.61
monoclinic
P21/c
646.03
triclinic
¯
P1
100(2)
100(2)
100(2)
100(2)
100(2)
λ [Å]
a [Å]
b [Å]
c [Å]
α [°]
β [°]
0.71073
12.9254(13)
7.1323(7)
24.719(3)
90
113.873(2)
90
2083.8(4)
4
1.872
1.313
0.31ϫ 0.27ϫ0.23
4960 (0.0390)
0.71073
12.9855(15)
7.0940(8)
24.637(3)
90
115.260(2)
90
2052.5(4)
4
1.855
1.330
0.27ϫ0.17ϫ0.13
4877(0.0514)
4007
0.71073
11.1343(14)
20.194(3)
8.5647(11)
90
105.204(2)
90
1858.3(4)
2
1.838
1.394
0.17ϫ0.13ϫ0.04
3862 (0.0639)
2998
0.71073
0.71073
8.7694(11)
10.5672(14)
11.6747(15)
73.364(2)
70.131(2)
80.474(2)
972.1(2)
28.540(2)
7.0078(6)
24.697(2)
90
120.7380(10)
90
4245.6(6)
4
2.106
γ [°]
V [Å3]
Z
2
Dcalc [gcm–3]
μ Mo-Kα [mm–1]
Crystal size [mm]
Unique reflections (Rint
2.207
2.675
0.32ϫ0.27ϫ0.19
4419 (0.0185)
4194
2.459
0.31ϫ0.28ϫ0.20
4995 (0.0390)
3965
)
Reflections with IϾ2σ(I) 4699
Refined parameters
R1[a], wR2[b][IϾ 2σ (I)]
R1[a], wR2[b](all data)
Goodness-of-fit on F2
275
295
243
253
313
0.0470, 0.1236
0.0488, 0.1250
1.099
0.0719, 0.1746
0.0892, 0.1834
1.098
0.0639, 0.1485
0.0840, 0.01584
1.050
0.0228, 0.0544
0.0247, 0.0554
1.075
0.0367, 0.0768
0.0525, 0.0829
1.001
3a
4a
5a
5b
5c
Formula
Formula weight
Crystal system
Space group
T [K]
C15H16AgF3N4O4S3 C14H14N4S2Ag·BF4 C14H14Ag2N6O6S2
C14H14N4S2AgNO3·xH2O C56H66Ag6N22O23S8
577.40
497.09
642.17
472.29
2319.01
triclinic
P1
triclinic
P1
triclinic
P1
triclinic
P1
triclinic
¯
¯
¯
¯
¯
P1
100(2)
100(2)
100(2)
100(2)
100(2)
λ [Å]
0.71073
0.71073
0.71073
0.71073
0.71073
a [Å]
b [Å]
c [Å]
α [°]
9.5218(13)
10.1352(14)
11.6408(16)
72.271(2)
74.598(2)
82.707(2)
1030.3(2)
2
1.861
1.340
0.34ϫ0.19ϫ0.17
4776 (0.0366)
7.1716(19)
11.525(3)
12.239(3)
107.444(4)
101.474(4)
107.357(4)
873.7(4)
2
1.889
1.439
0.24ϫ0.21ϫ0.03
4024 (0.0628)
3270
8.0267(8)
9.8371(10)
13.6870(14)
102.580(2)
102.482(2)
105.798(2)
970.30(17)
2
2.198
2.281
0.18ϫ0.09ϫ0.02
4451 (0.0333)
3806
9.5430(6)
11.6976(8)
17.2051(11)
84.1350(10)
82.6390(10)
79.7250(10)
1868.0(2)
4
1.679
1.325
0.23ϫ0.11ϫ0.03
8565 (0.0298)
7843
8.1077(4)
20.6967(12)
24.0920(13)
94.4590(10)
90.1730(10)
98.8550(10)
3982.0(4)
2
1.934
1.742
0.34ϫ0.27ϫ0.07
14825 (0.0513)
11831
β [°]
γ [°]
V [Å3]
Z
Dcalc [gcm–3]
μ Mo-Kα [mm–1]
Crystal size [mm]
Unique reflections (Rint
)
Reflections with IϾ2σ(I) 4148
Refined parameters
R1[a], wR2[b][IϾ 2σ (I)]
R1[a], wR2[b](all data)
Goodness-of-fit on F2
271
235
271
451
1106
0.0415, 0.0915
0.0501, 0.0958
1.040
0.0806, 0.1957
0.1013, 0.2079
1.048
0.0477, 0.1102
0.0594, 0.1163
1.047
0.0583, 0.1367
0.0646, 0.1398
1.167
0.0448, 0.0888
0.0612, 0.0945
1.031
[a] R1 = ∑||Fo| – |Fc||/∑|Fo|. [b] wR2 = {∑[w(Fo – Fc ) ]/∑[w(Fo2)2]}1/2
.
2
2 2
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947

L. Dobrzan´ska
FULL PAPER
cated on an inversion centre). The methanol molecule is ion in the asymmetric unit. There are no solvent molecules
coordinated to the metal centre and, to balance the charge, present. The silver ion is linearly coordinated by the two N
is partially deprotonated. The cationic complex in this com- atoms that originate from the imidazole rings of the chelat-
pound is triangular as the result of the conformation ing ligand (for bond lengths, see Table 2), and the ligand
adopted by the ligand, with one of the thioether bridges has a folded conformation with both thioether bridges on
pointing above and the other below the plane of the benz- the same side of the plane of the benzene ring (Table 3).
ene ring and the imidazole rings tilted towards each other The values of the two C–C–S–C torsion angles are dispro-
with a dihedral angle between their planes of 42.8(2)° (Fig- portionate, which causes the benzene ring to tilt to one side.
ure 3).
Argentophilic interactions are present (Table 4) and form a
dimeric species supported by π–π interactions between
neighbouring imidazole rings with a distance of 3.632(2) Å
between the corresponding centroids.
In the packing motif, cationic silver complexes linked in
dimers are stacked above each other (as in 1a and 1b) with
benzene rings from neighbouring columns in the same row
pointing in opposite directions (as they are related by an
inversion centre, Figure 4). The rows are separated by coun-
terions. N–H···F and C–H···F hydrogen bonds support the
close packing (Table S2).
Figure 3. Representation of the cationic complex in 1d with dis-
placement ellipsoids drawn at the 50% probability level.
The coordinated methanol molecule [Ag1–O21
2.568(6) Å] together with the imine N atoms from the che-
lating ligand form a T-shaped geometry around the Ag ion.
There are no argentophilic interactions present. The amine
N atom interacts with the counterions that are additionally
involved in interactions with the methanol molecules (Table
S2). Hydrogen bonding of the latter probably causes the
distortion from linearity of the N–Ag–N unit with an angle
of 167.9(2)°. Furthermore, π–π interactions are present be-
tween neighbouring N1–C5 imidazole rings as well as C–
H···π interactions between C12–H12···Cg2#6 [where Cg2 is
the centroid of the N1–C5 imidazole ring with a C···Cg2
distance of 3.324(6) Å] and C4–H4···S15#5 contacts [C···S
3.774(6) Å], which support the packing.
Figure 4. Representation of the packing viewed down the b axis for
2a (left) and 3a (right); argentophilic interactions are shown as
dashed grey lines.
[AgL]SbF6·1.5H2O (2b)
Complex 2b crystallises in the monoclinic space group
C2/c. There is one mononuclear cationic silver complex,
one counterion and 1.5 water molecules in the asymmetric
unit. The silver ion is linearly coordinated by two imine N
atoms from the chelating ligand (see Table 2), and the li-
gand adopts a folded conformation (see Table 3).
The cationic complex forms dimers that are held together
by argentophilic interactions, which are supported by weak
interactions between opposite imidazole rings with a
centroid–centroid distance of 3.653(3) Å (symmetry opera-
tion: 1/2 – x, 1/2 – y, –z). Looking down the b axis, the
packing of the cationic complexes resembles that of 1a/1b,
i.e. with the formation of rows that consist of dimeric units
with benzene rings from neighbouring columns pointing in
–
Crystal Structures of 2a and 2b Formed with SbF6 (Bulk
Material 2)
[AgL]SbF6 (2a)
¯
Complex 2a crystallises in the triclinic space group P1, the same direction. This enables C–H···π interactions,
–
with one cationic [AgL]+ complex and one SbF6 counter- namely, C11–H11···Cg1#7 (where Cg1 is the centroid of
Table 2. Selected bond lengths [Å] and angles [°] for mononuclear 1–5.
1a
1b
1d
2a
2b
3a
5b
Ag1–N1
Ag1–N17
Ag2–O21
N17–Ag1–1
N1–Ag1–O21
N17–Ag1–O21
2.088(3)
2.085(3)
2.090(6)
2.092(6)
2.113(5)
2.133(5)
2.568(6)
167.9(2)
89.20(18)
99.77(19)
2.108(2)
2.125(2)
2.095(3)
2.097(3)
2.109(3)
2.107(3)
2.133(5)/2.132(5)
2.134(4)/2.137(4)
173.39(11)
171.9(2)
170.63(7)
171.74(12)
172.28(11)
163.66(17)/163.39(1)
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AgI Complexes with a Flexible Ligand
–
Table 3. Torsion angles [°] that show the flexibility of the ligand in Crystal Structure of 3 Formed with CF3SO3
the AgI complexes, for corresponding values in 5c, see main text.
(Bulk Material 3)
C8–C7–S6–C2
C13–C14–S15-C16
[AgL]CF3SO3·H2O (3a)
1a
1b
1d
2a
2b
3a
4a
5a
5b
55.3(3)
–56.6(3)
¯
56.3(6)
170.3(4)
41.3(2)
52.9(4)
59.8(3)
71.9(7)
49.7(4)
63.9(5)/64.4(5)
–54.2(6)
–177.6(4)
–68.6(2)
–58.6(3)
–55.3(3)
–175.0(6)
–51.0(4)
–60.8(6)/–57.1(5)
Complex 3a crystallises in the triclinic space group P1
with unit cell parameters that are very similar to those ob-
served for 2a. Likewise, the packing is very similar to that
of 2a (Figure 4). The presence of water molecules and an
elongated counterion in the crystal lattice influences the
length of the a axis, which is ca. 0.75 Å longer than that in
2a. The b axis, however, is slightly shorter, which could be
caused by a small difference in the ligand conformation (see
Table 3). Interactions between water molecules, triflate and
the silver(I) complex further stabilise the packing (see Table
S2).
Table 4. Argentophilic interactions.[10]
Silver–silver interaction [Å]
–
Crystal Structures of 4a and 4b Formed with BF4
1a
1b
1d
2a
2b
3a
4a
5a
5b
5c
3.4459(6) intermolecular
3.3621(9) intermolecular
–
3.2378(5) intermolecular
3.3418(6) intermolecular
3.2845(6) intermolecular
3.4474(14) intermolecular
2.9558(6) intramolecular
–
(Bulk Material 4)
{[AgL]BF4}n (4a)
¯
Complex 4a crystallises in the triclinic space group P1.
The cationic AgI complex forms 1D zigzag chains along the
a axis, with the silver ions coordinated in a linear fashion
by imine N atoms that originate from two distinct ligands
(bridging mode, Figure 6). The conformation of the ligand
facilitates this type of assembly (see Table 3).
3.0919(5) and 3.2082(5) (moiety I) intramolecular
3.1376(5) and 3.1653(5) (moiety II)
benzene ring C8–C13) with a C···Cg1 distance of 3.468(5) Å
(Table S2). However, the hydrogen bonding net formed is
complicated by the presence of a higher number of solvent
molecules.
The water molecule with O28 acts as a bifurcated hydro-
gen-bond acceptor of the amine N–H from two distinct li-
gands and a hydrogen-bond donor in interactions with
counterions, whereas the remaining water molecule (O29)
interacts as a hydrogen-bond acceptor of one of the amine
N–H groups and as a donor to counterions (Table S2, Fig-
ure 5).
Figure 6. Fragment of the cationic chain in 4a; H atoms are omit-
ted for clarity; displacement ellipsoids drawn at the 50% prob-
ability level. Selected bond lengths [Å] and angles [°]: Ag1–N1
2.093(8), Ag1–N17i 2.065(7), N17–Ag1–N1i 175.5(3). Symmetry
i
operation: : x + 1, y, z.
The bond lengths in the cationic unit are more or less in
agreement with the distances observed for similar com-
pounds (vide supra) with a C2–S6 distance of 1.727(9) Å in
its shortest range [shorter bonds were reported for a CdII
complex with deprotonated 4-(2-benzimidazolethiomethyl)-
benzoic acid][11] and
a long C16–N17 distance of
1.369(11) Å (for 22 bond lengths of a similar kind found in
the crystal structure database, the mean is 1.324 Å).
The chains formed interact by argentophilic interactions
with neighbouring chains to result in infinite strands sup-
ported by π–π interactions between corresponding imid-
azole rings (N1–C5) and (C16–N20) with a centroid–
centroid distance of 3.722(6) Å and symmetry operation –
x, 2 – y, 1 – z. Weak C–H···F and N–H···F hydrogen bonds
between the cationic part and counterions stabilise the
Figure 5. Representation of the packing for 2b viewed down the
b axis; argentophilic interactions are shown as dashed grey lines,
hydrogen bonds that involve water molecules are shown as red lines. packing (see Table S2).
Eur. J. Inorg. Chem. 2012, 945–953
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949

L. Dobrzan´ska
FULL PAPER
[AgL]BF4·xCH3OH·xH2O (4b)
tween neighbouring Ag1 atoms (distance ca. 4.46 Å) are not
observed, which is due to the presence of the second silver
centre, Ag2. For the same reason, there are no π–π interac-
tions between imidazole rings from neighbouring units. In
addition, the unit cell parameters are comparable with
those of 2a and 3a with a shorter a axis, which is a result
of much smaller counterions, and a longer c axis because
of an additional silver atom.
The quality of the crystals of 4b was not sufficient to
fully characterise the structure (see Table S1). The com-
pound crystallises in the monoclinic space group P21/c with
unit cell parameters very similar to those obtained for 1a/
1b. The a and c axes are ca. 0.15 and 0.5 Å, respectively,
which are shorter than those of the corresponding solvate
1b and is attributed to the smaller size of the BF4– counter-
ion.
The packing is stabilised by weak C10–H10···Cg3#3 hy-
drogen bonds [where Cg3 is the centroid of C16–N20,
C10···Cg3 3.558(6) Å], as well as by many other weak C–
H···O and N–H···O hydrogen bonding interactions (see
Table S2).
–
Crystal Structures of 5a, 5b and 5c Formed with NO3
(Bulk Material 5)
[Ag2L(NO3)2] (5a)
[AgL]NO3·xH2O (5b)
Complex 5a crystallises in the centrosymmetric space
Complex 5b crystallises in the centrosymmetric space
¯
group P1 (triclinic system). It has a 2:1 Ag/L molar ratio
¯
group P1 (triclinic system) with two cationic mononuclear
even though it was isolated from bulk material prepared
with a molar ratio of 1:1. The resulting structure is unique
as L shows bischelating behaviour (Figure 7). Ag1 is coordi-
nated by imine N atoms to yield a linear geometry around
the metal centre, which is distorted from linearity by inter-
actions with nitrate counterions, namely, O24 [Ag–O
2.710(5) Å] and O23 [Ag–O 2.682(5) Å], which come from
a symmetry related counterion (symmetry operation: 1 –
x, –y, –z). Defining the above mentioned O atoms with an
Ag–O distance of ca. 2.7 Å as bonded, the complex could
be described as a dimer with a seesaw geometry around Ag1
and a τ4 value of 0.59.[12] Ag2 is chelated by S-donor atoms
that participate in its distorted tetrahedral environment
(AgS2O2), whereby O atoms (O21 and O25) originate from
two distinct nitrate counterions (τ4 = 0.71). Very strong in-
tramolecular argentophilic interactions are present between
the two metal centres, with a distance of ca. 2.96 Å, which is
only slightly longer than that for metallic silver (2.89 Å).[13]
metal complexes and two nitrate counterions in the asym-
metric unit. The conformation of the ligand differs only
slightly in the two cationic complexes. The silver ions are
linearly coordinated by imine N atoms that originate from
the chelating ligands (Figure 8), and the ligands adopt a
folded conformation.
Figure 8. Representation of the cationic complex in 5a with dis-
placement ellipsoids drawn at the 50% probability level.
There is a noticeable distortion of AgN2 from linearity
(see Table 2), which could be caused by weak interactions
with the nitrate O atoms [O23/O22A and O23A that are in
the proximity (ca. 3.1 Å) of Ag1/Ag1A, respectively]. Look-
ing down the a axis, columns of cationic complexes that
consist exclusively of Ag1 or Ag1A units stacked above
each other can be seen. The distance between the nearest
Ag1 and Ag1A in those columns is 4.1084(6) Å, which
shows the lack of interactions between these metal
centres.[10] Instead, the small nitrate counterions, which are
located between the C1–N5/C1A–N5A imidazole rings of
the stacked cationic units, form hydrogen bonds with the
NH group of these as well as with the NH group from C16–
N20/C16A–N20A of the adjacent columns. There are no π–
π interactions present in the packing, which is stabilised by
weak C–H···S and C–H···O interactions (Table S2). As the
solvent molecules could not be modelled, and the final
model was refined without them (by applying the
SQUEEZE routine of PLATON), full analysis of the re-
sulting packing was impossible.
Figure 7. Molecular structure of 5a with displacement ellipsoids
drawn at the 50% probability level; argentophilic interactions are
shown as dashed grey lines. Selected bond lengths [Å] and angles
[°]: Ag1–N1 2.152(4), Ag1–N17 2.161(4), N17–Ag1–N1 163.56(16),
Ag2–O21 2.334(4), Ag2–O25 2.417(4), Ag2–S6 2.539(1), Ag2–S15
2.475(1), O21–Ag2–O25 83.29(12), O21–Ag2–S15 146.52(9), O25–
Ag2–S15 98.72(9), O21–Ag2–S6 98.42(10), O25–Ag2–S6 102.93(9),
S15–Ag2–S6 113.41(4).
[Ag3L2NO3][Ag3L2H2O](NO3)5·4H2O (5c)
Not taking into account Ag2, the resulting packing
(looking down the b axis) is reminiscent of that of 2a and
3a. However, intermolecular argentophilic interactions be- group P1 (triclinic system) and, just as 5a, it shows an Ag/L
Complex 5c crystallises in the centrosymmetric space
¯
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Eur. J. Inorg. Chem. 2012, 945–953

AgI Complexes with a Flexible Ligand
molar ratio of 1.5:1, even though it originated from bulk coordinated O-donor ligands to form four-membered units.
material prepared with a molar ratio of 1:1. Interestingly, These are further interlinked by the counterion (N82) with
there are two crystallographically independent cationic tri- hydrogen bonds O81–H81A···O85 and N23–H23···O83#5
nuclear moieties present in the asymmetric unit, as well as into a 1D chain that expands along the b axis (Figure 10).
five nitrate counterions and four water molecules. Each cat-
ionic unit involves two folded L molecules with torsion
angles C8–C7–S6–C2 –50.7(5)°, C13–C14–S15–C16
48.4(5)°, C28–C27–S26–C22 –45.0(4)°, C33–C34–S35–C36
55.5(4)°, C48–C47–S46–C42 50.3(4)°, C53–C54–S55–C56
–53.4(4)°, C68–C67–S66–C65 52.9(4)°, C73–C74–S75–C78
–53.9(4)°. The ligands show bischelating (N,N- and S,S-)
behaviour as observed in 5a. Furthermore, in each moiety
there are three different geometries around the metal
centres present in the structure. Namely, a linear geometry
(AgN2) is formed by one N,N-chelating ligand, a distorted
tetrahedral environment (AgS4) is formed by two S,S-che-
lating ligands and a T-shaped (AgN2O) geometry is built
up by the second N,N-chelating ligand and, surprisingly, by
the counterion in one of the cationic moieties (moiety I)
and the water molecule in the other one (moiety II, Fig-
ure 9). As a result, these two cationic units have different
Figure 10. Fragment of the hydrogen bonded 1D chain in 5c that
consists of moieties I (orange) and II (green) shown in capped
sticks representation. Symmetry operations: i: –x + 1, –y + 1, –z +
charges. They interact by hydrogen bonds such as N80–
H80···O88, which involve the amine N atom from one of
the imidazole rings of moiety II and the O atom from the
coordinated nitrate anion (N86), and O81–H81B···O89#1
(for symmetry operation, see Table S2), which involve both
ii
1; : x, y + 1, z.
There are weak interactions present between Ag2 and
O91/O91A and O93/O93A from the disordered nitrate
counterion (N90) with distances of 2.70(2)–2.96(2) Å and
between Ag5 and O103, O104 from another counterion
(N102) with distances of 2.896(4) and 2.722(4) Å, respec-
tively. The counterions N90 and N94 form hydrogen bonds
with water molecule O115, which acts as a donor in this
case but it is also a bifurcated hydrogen-bond acceptor for
amine hydrogen atoms (H20–N20 and H40–N40). The
counterions, N98 and N102 and three water molecules, such
as O106, O109 and O112, form hydrogen bonded chains,
which run along the a axis and interact by N–H···O with
chains of cationic moieties to result in a 3D assembly. There
are also other weak hydrogen bonds that support the pack-
ing (Table S2).
It seems that only one of the amine N atoms (N60) is
not involved in the net of hydrogen bonds. A methanol mo-
lecule might have been present in the neighbourhood, which
was lost as the crystals dried, to cause disorder of the N90
nitrate counterion and also yield the small solvent access-
ible voids nearby in the crystal lattice (PLATON estimates
the accessible space to be 2.4% of the total cell volume).[14]
Intramolecular argentophilic interactions (Table 4) and
π–π interactions between imidazole rings (C16–N20 and
C37–N40, N41–C45 and N61–C65) with centroid–centroid
distances of ca. 3.4 Å are present in both trinuclear units.
Figure 9. Representation of the two trinuclear cationic moieties
with different O-donor ligands coordinated at one of the silver
centres present in the asymmetric unit of 5c. Hydrogen atoms and
some labels are omitted for clarity; displacement ellipsoids drawn
at the 50% probability level; intramolecular argentophilic interac-
tions are shown as dashed grey lines. Selected bond lengths [Å] and
angles [°]: (moiety I) Ag1–S15 2.538(1), Ag1–S35 2.558(1), Ag1–S6
2.603(1), Ag1–S26 2.604(1), N1–Ag2 2.115(4), Ag2–N 17 2.120(4),
Ag3–N21 2.120(4), Ag3–N37 2.121(4), Ag3–O87 2.642(3), S15–
Ag1–S35 112.77(4), S15–Ag1–S6 110.23(5), S35–Ag1–S6 120.64(5),
S15–Ag1–S26 115.85(5), S35–Ag1–S26 106.98(4), S6–Ag1–S26
88.27(4), N1–Ag2–N17 168.35(16), N21–Ag3–N37 167.82(15),
O87–Ag3–N21 85.19(13), O87–Ag3–N37 106.91(13); (moiety II)
Ag4–S46 2.547(1), Ag4–S66 2.548(1), Ag4–S75 2.619(1), Ag4–S55
2.623(1), Ag5–N57 2.103(4), Ag5–N41 2.121(4), Ag6–N61
2.137(4), Ag6–N77 2.141(4), Ag6–O81 2.467(3), S46–Ag4–S66
113.02(4), S46–Ag4–S75 122.81(4), S66–Ag4–S75 102.82(4), S46–
Ag4–S55 104.63(4), S66–Ag4–S55 123.51(4), S75–Ag4–S55
89.40(4), N57–Ag5–N41 169.19(15), N61–Ag6–N77 164.56(15),
N61–Ag6–O81 102.26(14), N77–Ag6–O81 93.11(14).
Conclusions
This paper tackles the problem of the characterisation of
the composition of bulk crystalline material. The presence
of mixtures can be easily overlooked by C, H, N elemental
analyses. It is still common practice among researchers to
select one crystal from the final crystalline material and to
Eur. J. Inorg. Chem. 2012, 945–953
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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951

L. Dobrzan´ska
FULL PAPER
crystal structures were determined: [Ag2L(NO3)2] (5a), [AgL]-
NO3·xH2O (5b) and [Ag3L2NO3][Ag3L2H2O](NO3)5·4H2O (5c).
The water in the crystals can be attributed to the presence of water
in the methanol and/or to air moisture, as the crystals were grown
by slow evaporation in ambient air (methanol in the crystal lattice
was replaced by water over time, as was noted before by the author
for similar systems).
present this specimen as representative for the entire solid
fraction. There is no requirement in journals to provide
powder patterns as a proof of phase purity for solid sam-
ples.[15] Therefore, the results can actually be very mislead-
ing and one might wonder how many papers describe elabo-
rate solid-state studies performed on a mixture of metal–
organic complexes. This is especially a risk in instances
where research is conducted on extended, flexible (often
multidonor) ligands and/or ligands that contain functional
groups or atoms that have a tendency to form hydrogen
bonds. In the latter case, the presence of solvates, and the
replacement of the crystallisation solvent molecules with
water upon exposure to air, seem to be very likely.[16] The
Structure Determination: Single-crystal X-ray diffraction data were
collected with a Bruker SMART APEX diffractometer equipped
with graphite monochromated Mo-Kα radiation (λ
=
0.71073 Å).[17a] The crystals were mounted on a glass fibre and
coated with Paratone-N oil. Data collection was carried out at
100(2) K to minimise solvent loss, possible structural disorder and
thermal motion effects. Cell refinement and data reduction were
coordinating abilities of the counterions complicate matters performed using the program SAINT[17b] and all empirical absorp-
tion corrections were performed using SADABS.[17c] Each structure
even further.
was solved by direct methods using SHELXS-97 and refined by
1,2-Bis[(imidazol-2-yl)thiomethyl]benzene (L) is a good
example of a ligand that is difficult to work with due to the
full-matrix least-squares methods based on F2 using SHELXL-
97.[17d] The program Mercury was used to prepare molecular
heterogeneity of the crystalline material obtained. The
graphics images.[17e] Hydrogen atoms, excluding those from OH
amine nitrogen atoms increase the affinity to form different
solvates through hydrogen bonding, which is not the case
for imidazole-based linkers without an available amine N
atom. The presence of additional S-donor atoms makes any
structural prediction even more complicated. The ligand
(water, methanol) were positioned geometrically with C–H 0.95
(aromatic), 0.98 (methyl) and 0.99 Å (methylene); N–H 0.88 Å
(aromatic) and refined as riding, with Uiso(H) = 1.2 Ueq (C, N) and
1.5 Ueq (methyl C). The remainder were located in a difference map
and refined with restrained O–H bond lengths. Data collection and
generally shows a tendency to form discrete N,N-bidentate structure refinement parameters are presented in Table 1. Crystal
mononuclear AgI complexes with a linear geometry around
the metal centre, induced by the chelating imine nitrogen
atoms of the folded ligand, with the imidazole rings approx-
imately coplanar. However, other modes of coordination
can also take place, such as N,NЈ-bridging, participation of
S-donor atoms or a T-shaped geometry around the silver
atom, brought about by the chelating N atoms of the ligand
in combination with solvent molecules or counterions.
Further studies that aim to control both the conforma-
structures 1a, 1d, 2a, 2b, 3a, 5a and 5c were deposited with the
CCDC. The remaining crystal structures 1b, 1c, 4a, 4b and 5b are
described briefly in the text (poor data quality for 1c and 4b does
not allow for in depth discussion). In 1b, the water molecule was
disordered and modelled in four positions. In 4a, the anisotropic
displacement parameters were restrained for C8, C9, C10 and N17.
In 5b, the electron density was subtracted and the SQUEEZE in-
struction of PLATON was applied[17f] as it was impossible to find
a suitable refinement model because of highly disordered water mo-
lecules. From this calculation we can estimate the presence of two
tion of the ligand and the coordination modes, which in- water molecules in the asymmetric unit. However, in the tabulated
data (Table 1) the molecular formula and weight, F(0 0 0) and ab-
sorption coefficient were not corrected for the presence of solvent
molecules. In this crystal structure, the anisotropic displacement
parameters were restrained for O43 and O48. In 5c one of the coun-
terions (N90) is disordered over two positions with refined site oc-
cupancies of 0.65(2):0.35(2). As a result, geometrical and displace-
ment-parameter restraints were applied to this anion.
volve exocyclic S-donor sites as in 5a and 5c, are ongoing.
Experimental Section
Reagents: All commercially available chemicals were of reagent
grade and were used without further purification. 1,2-Bis[(imida-
zol-2-yl)thiomethyl]benzene (L) was synthesised by the SN2 reac-
tion of 2-mercaptoimidazole with α,αЈ-dibromo-o-xylol in MeOH.
1H NMR (300 MHz, [D6]DMSO): δ = 12.16 (br. s, 2 H), 7.15 (m
4 H), 7.06 (s, 4 H), 4.34 (s, 4 H) ppm. 13C NMR (100 MHz,
[D6]DMSO): δ = 138.1, 135.9, 130.1, 127.6, 35.2 ppm. C14H14N4S2
(302.41): calcd. C 55.60, H 4.67, N 18.53; found C 55.49, H 4.89,
N 18.61.
CCDC-839088 (for 1a), -839089 (for 1d), -839090 (for 2a), -839091
(for 2b), -839092 (for 3a), -839093 (for 5a) and -839094 (for 5c)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Crystalline Bulk Materials: Compound 1 was obtained by the reac-
tion of AgPF6 with L. From this batch, four different crystal struc-
tures were determined: [AgL]PF6·CH3OH (1a), [AgL]PF6·H2O
(1b), [AgL]PF6·xCH3OH·xH2O (1c) and [AgLCH3O(H)0.5](PF6)0.5
(1d). Compound 2 was obtained by the reaction of AgSbF6 with
L. From this batch, two different crystal structures were deter-
mined: [AgL]SbF6 (2a) and [AgL]SbF6·1.5H2O (2b). Compound 3
was obtained by the reaction of AgCF3SO3 with L. From this
batch, one crystal structure was determined: [AgL]CF3SO3·H2O
(3a). Compound 4 was obtained by the reaction of AgBF4 with L.
From this batch, two crystal structures were determined: {[AgL]-
BF4}n (4a) and [AgL]BF4·xCH3OH·xH2O (4b). Compound 5 was
obtained by the reaction of AgNO3 with L. From this batch, three
Supporting Information (see footnote on the first page of this arti-
cle): Crystal data and details of the refinement parameters for the
crystal structures originating from crystalline bulk material 1–5
(Table S1). Parameters for hydrogen bonding in 1–5 (Table S2) as
well as figures presenting XRPD patterns for solids 1–5 (experi-
mental and calculated for isolated phases).
Acknowledgments
The author thanks the Research Foundation Flanders (FWO) for
financial support and the National Research Foundation (NRF) of
South Africa for supporting this work in its initial stage. Special
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Eur. J. Inorg. Chem. 2012, 945–953

AgI Complexes with a Flexible Ligand
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[3] a) C. A. Matuszak, A. J. Matuszak, J. Chem. Educ. 1976, 53,
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[6] Recently, a paper on the treatment of CdII complexes with 1,3-
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ylbenzene”.
[7] For structural studies on metal complexes with extended li-
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X.-H. Bu, W.-F. Hou, M. Du, W. Chen, R.-H. Zhang, Cryst.
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Received: August 16, 2011
Published Online: January 23, 2012
Eur. J. Inorg. Chem. 2012, 945–953
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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