Solvent-mediated conformational similarities within a series of 1D coordination polymers constructed from a new flexible ditopic bis-imidazole ligand

Article abstract of DOI:10.1039/c0nj00357c

A novel conformationally flexible ditopic ligand 1,3-bis(1-imidazolyl-2- thione)-2,4,6-trimethylbenzene (L), bearing thioether linkages between a central aromatic moiety and two pendant imidazole rings, was synthesised. Treatment of L with CdI₂ under varying conditions afforded four new solvates, {[CdLI₂]·H₂O}_n, {[CdLI ₂]·CH₃OH}_n, {[CdLI₂] ·2CH₃CN}_n, and {[CdLI₂]·2CH ₃OH}_n, which were characterised by single crystal X-ray diffraction. In all four of the complexes the Cd metal centers are tetrahedrally coordinated to two iodide ions and two nitrogen atoms from separate L molecules to form continuous 1D polymeric strands. The solvent molecules participate in strong hydrogen bonding with the amino nitrogen atoms of the imidazole rings. Hirshfeld surface analysis and breakdown of the corresponding 2D fingerprint plots of the four structures provide a convenient means of quantifying the interactions within the crystal structures, revealing significant similarities in the interactions experienced by each complex.

Full text of DOI:10.1039/c0nj00357c

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Solvent-mediated conformational similarities within a series of 1D
coordination polymers constructed from a new flexible ditopic
bis-imidazole ligandwz
Storm V. Potts and Leonard J. Barbour*
Received (in Victoria, Australia) 11th May 2010, Accepted 23rd June 2010
DOI: 10.1039/c0nj00357c
A novel conformationally flexible ditopic ligand 1,3-bis(1-imidazolyl-2-thione)-2,4,6-
trimethylbenzene (L), bearing thioether linkages between a central aromatic moiety and two
pendant imidazole rings, was synthesised. Treatment of L with CdI2 under varying conditions
afforded four new solvates, {[CdLI2]ꢀH2O}n, {[CdLI2]ꢀCH3OH}n, {[CdLI2]ꢀ2CH3CN}n, and
{[CdLI2]ꢀ2CH3OH}n, which were characterised by single crystal X-ray diffraction. In all four
of the complexes the Cd metal centers are tetrahedrally coordinated to two iodide ions and
two nitrogen atoms from separate L molecules to form continuous 1D polymeric strands.
The solvent molecules participate in strong hydrogen bonding with the amino nitrogen atoms
of the imidazole rings. Hirshfeld surface analysis and breakdown of the corresponding
2D fingerprint plots of the four structures provide a convenient means of quantifying the
interactions within the crystal structures, revealing significant similarities in the interactions
experienced by each complex.
ligands and transition metals, we have prepared a novel
Introduction
ditopic ligand bearing thioether linkages between a central
Transition-metal based supermolecules have been recognised
for their potential use in optics,1 gas sorption2 and catalysis,3
aromatic moiety and two pendant imidazole rings, namely 1,3-
bis(1-imidazolyl-2-thione)-2,4,6-trimethylbenzene (L, Scheme 1).
but control of the architectures derived from the self-assembly
Herein, we report the synthesis and crystal structures of
of transition metal salts and flexible organic bridging ligands
four new solvates of one dimensional (1D) Cd(II) coordination
remains an elusive aspect of crystal engineering.4 To date,
polymers constructed from L and CdI2.
most metal–organic frameworks have been constructed using
We note that variation of the solvent, as well as the solvent-
rigid ligands (mostly containing pyridyl and carboxylate
to-complex ratio results in subtle changes in the packing of the
functionalities) owing to the relative ease of prediction of the
1D chains. In addition to conventional packing analysis, we
resulting networks and the limited conformational changes
have also inspected the intermolecular interactions in the
crystal structures by means of Hirshfeld surface analysis9
that can occur. However, the interest in comparatively
flexible organic bridging ligands is on the rise because the
and by considering the characteristic regions of the
conformational diversity of these ligands could facilitate the
corresponding 2D fingerprint plots for an individual complex
in each structure.10
discovery of unique frameworks, and thus contribute further
understanding of the manner in which supramolecular
architectures assemble.5
Imidazole functionalised compounds constitute a class of
N-donor organic ligands that have attracted increasing
attention owing to their high affinity for metals and their
relative ease of preparation.6 Indeed, we7 and others8 have
shown that imidazole-based bridging ligands have a rich
coordination chemistry that can be successfully exploited to
construct a range of coordination networks with interesting
topologies and properties.
As part of our ongoing interest in the supramolecular
structures derived from the reaction of imidazole-functionalised
Department of Chemistry, University of Stellenbosch,
Stellenbosch 7600, South Africa. E-mail: ljb@sun.ac.za;
Fax: +27 21 808 3360; Tel: +27 21 808 3335
Scheme 1 (a) 1,3-Bis(1-imidazolyl-2-thione)-2,4,6-trimethylbenzene
(L). (b) In the UD conformation the two imidazolyl rings (represented
w This article is part of a themed issue on Coordination polymers:
as yellow and red spheres respectively) are situated on the opposite
structure and function.
sides and (c) in the UU conformation they are situated on the same
z CCDC reference numbers 776909–776912. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/c0nj00357c
side of the aromatic core plane.
c
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Table 1 Coordination geometric parameters for complexes 1–4
Results and discussion
1
2
3
4
The bidentate ligand L was synthesized by the SN2 reaction
of 2-mercaptoimidazole with 2,4-bis(chloromethyl)-1,3,5-
trimethylbenzene in MeOH. Although the imidazolyl rings
and aromatic core are rigid, the connections between the two
‘‘arms’’ and the core (i.e. the methylene group and sulfur
bridge) allow the arms to rotate freely in solution. Owing
to this flexibility the ligand can assume a UU (or up–up)
conformation, where the two imidazolyl rings are situated on
the same side of the central aromatic core, or a UD (up–down)
conformation, where the two rings are positioned on opposite
sides of the core (Scheme 1b and c). Diffraction-quality single
crystals of complexes 1, 2 and 4 (Fig. 1) were obtained by the
reaction of L with CdI2 (in ligand-to-metal molar ratios of
1 : 1, 2 : 1 and 1 : 2, respectively) in MeOH, followed by slow
evaporation of the solvent. Single crystals of complex 3 were
obtained from a 1 : 1 solution of L and CdI2 in MeCN,
followed by slow evaporation of the solvent.
Bond lengths (A)
Cd1–I1
Cd1–I2
Cd1–N1
2.7575(6)
2.7564(6)
2.221(3)
2.239(3)
2.7720(5)
2.6844(5)
2.253(4)
2.265(4)
2.7332(5)
2.7341(5)
2.240(4)
2.268(4)
2.7482(7)
2.7424(7)
2.223(5)
2.226(5)
Cd1–N20i
Bond angles (1)
I2–Cd1–I1
N1–Cd1–I1
N20i–Cd1–I1
N1–Cd1–I2
N20i–Cd1–I2
116.74(2)
106.62(9)
107.08(9)
114.50(9)
101.38(9)
119.718(17) 115.638(18) 120.28(2)
102.63(9)
101.34(9)
120.63(9)
110.51(9)
112.88(11)
104.62(11)
114.25(11)
107.13(10)
100.43(15)
101.48(13)
106.82(13)
107.47(12)
103.73(13)
117.94(19)
N1–Cd1–N20i 110.14(13) 98.44(13)
Symmetry codes for 1: (i) x, y ꢁ 1, z; for 2: (i) x, y + 1, z; for 3:
1
2
(i) x, y + 1, z; for 4: (i) x, ꢁy + 2, z + .
Table 2 Hydrogen-bond geometry for complexes 1–4
D–Hꢀ ꢀ ꢀA
1
Dꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA
3
Dꢀ ꢀ ꢀA
Structural analysis of complexes 1–4
N4–H4ꢀ ꢀ ꢀO24
N23–H23ꢀ ꢀ ꢀO24
O24–H24Aꢀ ꢀ ꢀI1i
O24–H24Bꢀ ꢀ ꢀI2i
2
N4–H4ꢀ ꢀ ꢀO24
N23–H23ꢀ ꢀ ꢀO24
O24–H26ꢀ ꢀ ꢀI1ii
2.811(5)
2.768(5)
3.508(3)
3.589(3)
N4–H4ꢀ ꢀ ꢀN24
2.901(6)
2.909(6)
{[CdLI2]ꢀH2O}n (1). Single crystal X-ray diffraction analysis
reveals that complex 1 forms a 1D strand propagating along
[010]. Adjacent Cd-ions are connected by means of a single
ligand L in the UU conformation and the dihedral angles
between the planes of the two imidazole rings and the benzene
ring are 28.5(1)1 and 30.3(2)1. Each metal center is coordinated
to two iodine ions and two nitrogen atoms from separate
ligand molecules to form a distorted tetrahedral coordination
environment around each metal ion. The coordinating angles
range from 101.38(9)1 to 116.74(2)1 and the parameters
relevant to the coordination geometries are given in Table 1.
In addition to the constituents that form part of the 1D
chain, the asymmetric unit (ASU) also contains one water
molecule. The two imidazole amino nitrogen atoms belonging
to the same ligand molecule simultaneously donate two
hydrogen bonds to this water molecule, thus stabilizing the
overall UU conformation of the ligand (Table 2). Neighbouring
N23–H23ꢀ ꢀ ꢀN24
4
2.836(5)
2.812(5)
3.436(3)
N4–H4ꢀ ꢀ ꢀO26
N23–H23ꢀ ꢀ ꢀO24
O26–H26ꢀ ꢀ ꢀI2iii
O28–H28ꢀ ꢀ ꢀI1iv
2.713(8)
2.723(10)
3.441(5)
3.421(12)
3
2
1
3
1
2
Symmetry codes: (i) x, ꢁy + , z ꢁ ; (ii) ꢁx + , ꢁy + , ꢁz + 1;
2
2
(iii) x, y + 1, z; (iv) 1 ꢁ x, 1 + y, 32 ꢁ z. Parameters involving hydrogen
atoms have not been included since their positions are not reliable.
1D strands are connected to form a distorted 2D honeycomb
arrangement by the donation of two hydrogen bonds from the
water molecule to the coordinated iodine atoms (Fig. 2, top).
The honeycomb layer is connected to another layer by means
of offset face-to-face p–p interactions between neighbouring
benzene rings (centroid–centroid distance = 3.569 A) and, as
a result, the honeycomb layers stack on top of one another
such that the atoms of the first layer eclipse those of the third
layer when viewed along [100] (Fig. 2, bottom).
{[CdLI2]ꢀCH3OH}n (2). The ASU of 2 is similar to that of 1
both in terms of its constituents as well as the relative
arrangement of its components (Fig. 1). However, in 2 a
methanol molecule occupies the position of the water molecule
in 1, assuming the role of a bifurcated hydrogen bond acceptor
to the nitrogen donors of the imidazole groups to stabilize the
UU conformation of the ligand. The dihedral angles between
the planes of the two imidazole rings and that of the phenylene
ring are 31.8(3)1 and 37.6(2)1, respectively. The unique angles
that complete the distorted tetrahedral environment around
the Cd metal center range from 98.44(1)1 to 120.63(9)1
and successive metal centers are linked to one another via
individual ligand molecules to form a 1D polymeric chain
running parallel to [010]. The methanol molecule donates a
hydrogen bond to one of the ligated iodide ions of an adjacent
strand (Fig. 3), thus connecting adjacent 1D chains into
bilayers (see Table 2 for hydrogen bonding parameters).
Fig. 1 Atomic displacement (50% probability plots) showing the
asymmetric units of complexes 1–4. Hydrogen atoms are shown as
spheres of arbitrary radius and hydrogen bonds are shown as dashed
red lines. In the case of 4, one of the methanol molecules is disordered
over two sites as shown.
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Fig. 4 Packing arrangement of the 2D layers formed in 2, as viewed
along [010]. Molecules are shown in the capped-stick metaphor;
hydrogen bonds and p–p stacking interactions are shown as dashed
red and green lines, respectively.
Fig. 5 Ball-and-stick plot showing the 1D strand formed in 3, as
Fig. 2 Distorted 2D honeycomb layer (top) formed by hydrogen
bonding in 1. Molecules are shown in the ball-and-stick metaphor.
viewed down [100]. Hydrogen bonds are shown as dashed red lines.
A
simplification of the 2D honeycomb layers (bottom) shows
the . . .ABAB. . . stacking arrangement. Both projections are viewed
phenylene (centroid–centroid distance
=
3.818 A) and
and
along [100].
imidazole (centroid–centroid distances of 3.538
A
3.794 A apply) rings to form 2D sheets running parallel to
(100) (Fig. 6).
{[CdLI2]ꢀ2CH3OH}n (4). The ASU of 4 consists of one
ligand L, two iodine ions and two methanol molecules
(see Fig. 1). One of the methanol molecules is disordered over
two positions. The Cd ion is coordinated to two iodine
counter-ions and two imidazole nitrogen atoms of separate
L molecules. This results in a distorted tetrahedral coordina-
tion geometry around the metal ion (coordinating angles range
from 101.48(13)1 to 120.28(2)1). Neighbouring metal centres
are connected to each other via a single ligand L to form a 1D
zigzag polymeric strand running parallel to [101] (Fig. 7). Each
ligand assumes the UD conformation with the coordinating
Fig. 3 Capped-stick representation showing the hydrogen bonds
formed in 2. Atoms of the fragment at the top are related to those
at the bottom by the symmetry operation 3/2 ꢁ x, 1/2 ꢁy, 1 ꢁ z.
Hydrogen bonds are shown as dashed red lines.
Fig. 4 shows the 2D assembly in which the bilayers are
connected to one another by p–p stacking interactions
between adjacent benzene rings (centroid–centroid distance =
4.112 A).
{[CdLI2]ꢀ2CH3CN}n (3). Complex 3 also features L in the
UU conformation. The ASU is similar to that of the previous
two structures, except that it contains two acetonitrile solvent
molecules (Fig. 1). As observed in 1 and 2, one solvent
molecule acts as a bifurcated hydrogen bond acceptor for
the amino nitrogen donors of the imidazole groups (Table 2).
Complex 3 forms 1D strands similar to those of 1 and 2; these
strands also run parallel to [010] (Fig. 5).
Fig. 6 Capped-stick representation of the 2D layers formed in 3 as
viewed along [100]. Hydrogen atoms and solvent molecules have been
omitted for clarity and p–p stacking interactions have been shown as
dashed green and red lines between phenylene and imidazole rings,
respectively.
All neighbouring strands interact with one another by
means of weak offset face-to-face p–p interactions between
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Fig. 7 A single 1D strand of 4 running parallel to [101]; thick green
lines are shown to emphasise the zigzag character of the strand;
molecules are shown in the capped-stick metaphor.
nitrogen atoms of the imidazole groups oriented in opposite
directions. The dihedral angles between the imidazole and
benzene ring planes are 37.9(3)1 (for the ring containing N1)
and 5.2(5)1 (for the ring containing N20).
Fig. 9 The bilayers in 4 as viewed along [010]. p–p interactions are
shown as dashed red lines imidazole ring centroids. Separate strands
within each bilayers are coloured green and blue. Hydrogen atoms and
solvent molecules are omitted for clarity and molecules are shown in
the capped-stick metaphor.
Each methanol molecule accepts a hydrogen bond from
an uncoordinated imidazole nitrogen atom. One of
these methanol molecules then donates a hydrogen bond
(O26ꢀ ꢀ ꢀI2 = 3.441(5) A) to one of the coordinated iodine ions
and, through this series of cooperative hydrogen bonds,
adjacent 1D strands are linked into a 2D brick wall network
parallel to (100) (Fig. 8, see Table 2 for details of hydrogen
bonding parameters). Each layer is then connected to one
other layer by means of offset face-to-face p–p interactions
between neighbouring imidazole rings (centroid–centroid
distance = 3.569 A) to form a bilayer (Fig. 9). The second
methanol molecule is disordered over two positions; both
positions are such that the hydroxyl oxygen atom accepts an
N–Hꢀ ꢀ ꢀO hydrogen bond from an imidazole amino nitrogen
atom (N23). One of the disordered orientations can donate
an O–Hꢀ ꢀ ꢀI hydrogen bond and the other orientation can
accommodate an O–Hꢀ ꢀ ꢀ p interaction to a phenylene ring.
in the case of 3 since the CH3CN solvent can only act as a
hydrogen bond acceptor.
The ligand adopts the UU conformation in complexes 1, 2
and 3. In all three of these structures the amino nitrogen atoms
of the imidazole rings donate hydrogen bonds to the solvent
molecules, and in this role of bifurcated hydrogen bond
acceptor, the solvent molecule most likely stabilises the
UU conformation. This conformation also facilitates the
formation of p–p stacking interactions between phenyl rings
of adjacent 1D strands in 2 and 3, and adjacent 2D layers in 1.
In contrast to 1–3 the two solvent molecules in 4 are not
involved in bifurcated hydrogen bonding, instead each MeOH
molecule is hydrogen bonded to one uncoordinated nitrogen
atom of an imidazole group. The ligand adopts the UD
conformation, and the benzene rings are not able to partici-
pate in p–p stacking interactions.
There are significant similarities in the intermolecular inter-
actions within the crystal structures of all four complexes. A
convenient way to view and quantify these intermolecular
interactions is by mapping a Hirshfeld surface11 onto a frag-
ment of each complex using the program CrystalExplorer12
and then generating the corresponding 2D fingerprint plot.13
By definition a Hirshfeld surface is a means of dividing space
Comparison of structures 1–4
In each complex a 1D polymeric strand is formed in which the
Cd-ion is tetrahedrally coordinated to two iodide ions and two
nitrogen atoms belonging to separate L molecules. It is
interesting to note that a 1 : 1 ligand-to-metal ratio persists
in all of the solid-state structures, even though the solution
ligand-to-metal ratio was varied. Each crystal structure also
contains solvent molecules that participate in hydrogen
bonding interactions; when the structure contains H2O or
MeOH (i.e. 1, 2 and 4), 1D strands are formed that link
to adjacent strands by virtue of strong solvent-bridged
hydrogen bonds; weak p–p interactions served this purpose
in
a crystal into regions of electron density and the
actual surface is defined by the portion of space where
the promolecule electron density contributes exactly half of
the total procrystal electron density (the terms promolecule
and procrystal refer to the spherical atoms of the molecule of
interest and to the atoms of the whole crystal, respectively).9
The molecular Hirshfeld surface thus encloses a single
molecule within the crystal and provides a smooth surface
onto which certain scalar properties (for example, contact
distances) can be mapped. For each point on the surface,
two distances are defined: di, the distance from the surface to
the nearest atom interior to the surface, and de, the distance
from the surface to the nearest atom exterior to the surface.
The 2D fingerprint plot is constructed by binning the di and de
pairs in intervals of 0.01 A, thereby creating a 2D histogram
that reflects all the intermolecular interactions of the molecule.
Each bin is coloured according to the fraction of surface
points in that bin.10
Fig. 8 Projection perpendicular to (100) of the 2D brick wall network
of 4 formed by hydrogen bonding; one 1D strand has been highlighted
in green and all molecules are shown in the capped stick representation.
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In order to generate the surfaces for 1–4, a single fragment
of each complex first needed to be defined; for the purposes of
this study a fragment was taken to be a single CdLI2 unit
within the 1D coordination polymer chain in each crystal
structure. It should be noted that, to date, all examples in
the literature that have made use of Hirshfeld surface analyses
have done so on crystal structures containing discrete
molecules or complexes and that, to the best of our knowledge,
ours is the first report of a surface being generated for a
fragment comprising a metal–organic unit within a 1D
coordination polymer. We also note that this approach must
be taken and interpreted with great care since the software is
insensitive to the differences between inter- and intramolecular
contacts. When two or more polymeric structures are
compared and contrasted by means of the Hirshfeld surface
analysis, the extended systems should be truncated in a similar
manner, and the intramolecular contacts should be clearly
indicated.
Fig. 11 Percentage contributions to the Hirshfeld surface area for
various contacts in complexes 1–4.
hydrogen bond donor and the lower wing with the hydrogen
bond acceptor. In all four of the plots this interaction is
coloured blue-green, indicating that a larger proportion of
points on the Hirshfeld surface are involved in interactions of
this nature.
Based purely on a visual inspection of the fingerprint plots
in Fig. 10 it appears that the structures have several features in
common but these features are more similar to one another in
complexes 1–3 than those in complex 4. One of the most
obvious common features is the sharp spike labelled A in the
vicinity of (di, de) E (0.7, 1.1 A). This interaction is attributed
to the hydrogen bond between the imidazole amino nitrogen
atoms and the solvent molecules i.e. the N–Hꢀ ꢀ ꢀO hydrogen
bond in complexes 1, 2 and 4 and the N–Hꢀ ꢀ ꢀN hydrogen
bond in 3 and, as might be expected, a slightly longer inter-
action is apparent for 3. A second prominent ‘‘interaction’’
(labelled B) indicates the coordination bond between the Cd
and N atoms, which appear as a pair of spikes at the bottom
left of the plots (i.e. at low di and de values). The short head-to-
head Hꢀ ꢀ ꢀH contacts (labelled C) at the limit of the van der
Waals radii appear as a characteristic narrow hump between
peaks B for complexes 1–4. The ‘wings’ at D indicate the
Hꢀ ꢀ ꢀI hydrogen bonds—the upper wing is associated with the
Fig. 11 contains the percentage contributions for a variety
of contacts in the complexes. From these values it can be seen
that the Cꢀ ꢀ ꢀC contacts, associated with p–p stacking inter-
actions in the (di, de) E (1.8, 1.8 A) region, are minimal in 4
(only 0.5% of the surface is due to Cꢀ ꢀ ꢀC interactions compared
with the 2.2, 1.8 and 3.5% for 1, 2 and 3, respectively); this
quantitatively verifies observations that are obvious from
inspecting the different structures. However, it is interesting
to note that the Hꢀ ꢀ ꢀS contacts are associated with a
significant percentage of the surface area (9.0, 6.8, 6.2 and
7.9% for 1, 2, 3 and 4, respectively), a feature that might
otherwise have gone unnoticed if the packing had been
analysed by inspection alone.
Conclusion
In summary, a novel conformationally flexible ditopic ligand
was synthesised and reacted with CdI2 under varying
conditions to yield four new solvates consisting of 1D
coordination polymeric strands. These four complexes were
characterised structurally by single crystal X-ray diffraction,
which reveals that complex 1 contains a single water molecule
that participates in hydrogen bonding to link the 1D polymeric
strands into a distorted 2D honeycomb network, whereas
complex 2 contains a single MeOH molecule that participates
in hydrogen bonding that connects adjacent strands into
bilayers. Complex 3 contains two MeCN molecules; however
it is the weaker p–p interactions that serve to connect
neighbouring strands. Although complex 4 contains two
molecules of MeOH, only one is utilised to connect the 1D
strands into a 2D brick-wall network. These structures imply
that it is not only the nature of solvent molecule that affects
the packing arrangement, but that subtle changes in the
conformation of the ligand results in variation in the crystal
packing.
Finally, we have shown that the fingerprint plots generated
by CrystalExplorer provide a convenient means of visualising
and comparing the intermolecular interactions of a series of
structurally related polymeric complexes.
Fig. 10 Fingerprint plots of complexes 1–4; refer to text for clarifica-
tion of the labels.
c
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X-Ray crystallography
Experimental
Single crystals of compounds 1–4 were harvested directly from
the slow evaporation preparations and in all cases suitable
single crystals (i.e. those found by inspection to have
well-defined morphology and that extinguished plane
polarised light uniformly) were attached to the end of a
MiTeGen mount using paratone oil. Intensity data were
collected on a Bruker SMART Apex CCD single-crystal
X-ray diffractometer14 equipped with an Oxford Cryosystems
Cryostream Plus cooling system set at 100 K. The system
was operated at 1.2 kW power (40 kV, 30 mA) using mono-
chromated Mo-Ka radiation (l = 0.71073 A). Data reduction
was carried out by means of a standard procedure using
the Bruker SAINT software package.15 Where necessary,
empirical corrections were performed using SADABS.16,17
All crystal structures were solved and refined using SHELX-97.18
X-Seed19 was used as a graphical interface for SHELX.
Structures were solved either by direct methods or a combination
of Patterson methods and partial structure expansion using
SHELXS-97. Structures were expanded by iterative examina-
tion of difference Fourier maps following least squares
refinements of earlier models. All non-hydrogen atoms were
refined anisotropically by means of full-matrix least squares
calculations on F2 using SHELXL-97. Where appropriate,
hydrogen atoms were placed in calculated positions using
riding models and assigned isotropic thermal parameters
1.2–1.5 times Ueq of their parent atoms. Hydroxyl and water
hydrogen atoms were located in difference electron density
maps and refined independently.
All reagents and solvents were purchased and used as received.
IR spectra were recorded on a Nexus 670 FT-IR instrument
(Thermo Nicolet Instruments, USA) in the spectral range
4000–400 cmꢁ1 using the KBr pellet method. LC ESI-MS
analysis was carried out on a Waters API Quattro Micro mass
spectrometer with an electrospray ionisation source and
1H-NMR and 13C-NMR spectra were recorded on a Varian
Unity INOVA (400 MHz).
Synthesis of 1,3-bis(1-imidazolyl-2-thione)-2,4,6-trimethyl-
benzene (L)
2-Mercaptoimidazole (2.01 g, 20 mmol) was added to 2,4-
bis(chloromethyl)-1,3,5-trimethylbenzene (1.09 g, 5.0 mmol) in
200 mL of MeOH. The resulting solution was refluxed for 24 h.
The solvent was then removed under reduced pressure and
yielded a yellow oil, to which K2CO3 (6.91 g, 50 mmol) in
100 mL of H2O was added. The solution was stirred until the
product precipitated. The white solid was then filtered, washed
with 100 mL H2O and left to air dry. Yield: 92.5%. Mp:
168–170 1C; IR (KBr pellet): nmax 3434 (N-H of Im), 2363,
1858, 1605 (aromatic CQC), 1547, 1414 (CH2 bend), 1232
(CH2–S wag), 1096, 963, 746 cmꢁ1 1H-NMR (DMSO-D6,
;
400 MHz): d 2.18 (3H, s, ArCH3), 4.14 (4H, s, CH2S), 6.91
(2H, s, ArHa), 6.94 (1H, s, ArHb), 7.05 (4H, s, CN(H)CHCHN);
13C-NMR (DMSO-D6, 75.5 MHz): d 20.69, 37.6, 123.7, 126.1,
137.5, 137.7, 138.3; MS (ESI+): m/z 317 (100%, [(M + H]+)],
218 (20%, M+ ꢁ SIm), 159 (87%).
Preparation of complexes 1–4
Crystal data for 1. C17H22CdI2N4OS2, M = 728.71, colourless
plate, 0.11 ꢂ 0.09 ꢂ 0.06 mm, monoclinic, space group P21/c
(No. 14), a = 13.470(3), b = 11.610(3), c = 15.371(3) A,
Synthesis of {[CdLI2]ꢀH2O}n (1). 10.1 mg L (0.029 mmol)
was dissolved in 3 mL of MeOH and added to 10.6 mg
(0.029 mmol) CdI2 dissolved in 2 mL MeOH. The solvent
was allowed to evaporate slowly and after a period of 3 weeks
colourless crystals formed, and the structure was elucidated by
single-crystal X-ray diffraction.
b = 99.904(4)1, V = 2367.9(9) A3, Z = 4, Dc = 2.044 g cmꢁ3
,
F000 = 1384, Mo-Ka radiation, l = 0.71073 A, T = 100(2) K,
2ymax = 56.51, 14 624 reflections collected, 5506 unique
(Rint = 0.0349). Final GooF = 1.076, R1 = 0.0378, wR2 =
0.0827, R indices based on 4801 reflections with I > 2s(I)
(refinement on F2), 255 parameters, 3 restraints. Lp and
Synthesis of {[CdLI2]ꢀCH3OH}n (2). 20.2 mg L (0.058 mmol)
was dissolved in 3 mL of MeOH and added to 10.6 mg
(0.029 mmol) CdI2 dissolved in 2 mL MeOH. The solvent
was allowed to evaporate slowly and after a period of one
month colourless crystals formed, and the structure was
elucidated by single-crystal X-ray diffraction.
absorption corrections applied, m = 3.720 mmꢁ1
.
Crystal data for 2. C18H24CdI2N4OS2, M = 742.73, 0.24 ꢂ
0.17 ꢂ 0.11 mm, monoclinic, space group C2/c (No. 15), a =
31.625(3), b = 11.0517(10), c = 16.3433(15) A, b =
119.0840(10)1, V = 4992.0(8) A3, Z = 8, Dc = 1.977 g cmꢁ3
,
F
000 = 2832, Mo-Ka radiation, l = 0.71073 A, T = 100(2) K,
Synthesis of {[CdLI2]ꢀ2CH3CN}n (3). 10.1 mg L (0.029 mmol)
was dissolved in 3 mL of MeCN and added to 10.6 mg
(0.029 mmol) CdI2 dissolved in 2 mL MeCN. The solvent
was allowed to evaporate slowly and after a period of 2 weeks
colourless crystals formed, and the structure was elucidated by
single-crystal X-ray diffraction.
2ymax = 56.61, 15 354 reflections collected, 5813 unique
(Rint = 0.0339). Final GooF = 1.060, R1 = 0.0396, wR2 =
0.0885, R indices based on 4948 reflections with I > 2s(I)
(refinement on F2), 258 parameters, 0 restraints. Lp and
absorption corrections applied, m = 3.532 mmꢁ1
.
Crystal data for 3. C21H22CdI2N6S2, M = 792.80, 0.180 ꢂ
ꢀ
Synthesis of {[CdLI2]ꢀ2CH3OH}n (4). 10.1 mg L (0.029 mmol)
was dissolved in 3 mL of MeOH and added to 21.2 mg
(0.058 mmol) CdI2 dissolved in 2 mL MeOH. The solvent
was allowed to evaporate slowly and after a period of 3 weeks
colourless crystals formed, and the structure was elucidated by
single-crystal X-ray diffraction.
0.120 ꢂ 0.080 mm, triclinic, space group P1 (No. 2), a =
9.6481(9), b = 11.2186(10), c = 14.1622(13) A, a =
112.0230(10), b = 91.681(2), g = 101.926(2)1, V = 1380.7(2) A3,
Z = 2, Dc = 1.907 g cmꢁ3, F000 = 760, Mo-Ka radiation,
l = 0.71073 A, T = 100(2) K, 2ymax = 56.61, 16003 reflections
collected, 6381 unique (Rint = 0.0425). Final GooF = 1.080,
c
2456 New J. Chem., 2010, 34, 2451–2457 This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010

View Article Online
R1 = 0.0478, wR2 = 0.1147, R indices based on 5475
reflections with I > 2s(I) (refinement on F2), 294 parameters,
0 restraints. Lp and absorption corrections applied, m =
4 (a) B. Moulton and M. J. Zaworotko, Chem. Rev., 2001, 101, 1629;
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3.198 mmꢁ1
.
Crystal data for 4. C19H28CdI2N4O2S2, M = 774.77, 0.22 ꢂ
0.10 ꢂ 0.07 mm, monoclinic, space group C2/c (No. 15), a =
32.585(4), b = 10.2983(14), c = 19.944(3) A, b = 125.829(2)1,
V = 5426.1(13) A3, Z = 8, Dc = 1.897 g cmꢁ3, F000 = 2976,
7 (a) L. Dobrzan
Chem., 2008, 32, 813; (b) L. Dobrzan
L. J. Barbour, New J. Chem., 2007, 31, 669; (c) L. Dobrzan
´
ska, D. J. Kleinhans and L. J. Barbour, New J.
ska, G. O. Lloyd and
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´
´
G. O. Lloyd, T. Jacobs, I. Rootman, C. L. Oliver,
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Mo-Ka radiation, l = 0.71073 A, T = 100(2) K, 2ymax
=
56.71, 16 699 reflections collected, 6331 unique (Rint = 0.0525).
Final GooF = 1.068, R1 = 0.0567, wR2 = 0.1080, R indices
based on 4832 reflections with I > 2s(I) (refinement on F2),
278 parameters, 7 restraints. Lp and absorption corrections
(f) L. Dobrzan
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.
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Acknowledgements
We thank the National Research Foundation and the Depart-
ment of Science and Technology for support of this work.
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