Construction of one- and two-dimensional coordination polymers using ditopic imidazole ligands

Article abstract of DOI:10.1016/j.molstruc.2006.02.059

A series of ditopic imidazole functionalised ligands have been investigated for their propensity to form one- and two-dimensional coordination polymers with a range of metals. We show that ditopic imidazole ligands have the versatility to be exploited in

Full text of DOI:10.1016/j.molstruc.2006.02.059

Journal of Molecular Structure 796 (2006) 107–113
www.elsevier.com/locate/molstruc
Construction of one- and two-dimensional coordination polymers
using ditopic imidazole ligands
1
Liliana Dobrzanska , Gareth O. Lloyd, Tia Jacobs, Ilse Rootman, Clive L. Oliver,
´
*
Martin W. Bredenkamp, Leonard J. Barbour
Department of Chemistry, University of Stellenbosch, Matieland 7602, South Africa
Received 31 January 2006; received in revised form 24 February 2006; accepted 24 February 2006
Available online 3 May 2006
Abstract
A series of ditopic imidazole functionalised ligands have been investigated for their propensity to form one- and two-dimensional coordination
polymers with a range of metals. We show that ditopic imidazole ligands have the versatility to be exploited in the formation of a variety of
coordination polymers.
q 2006 Elsevier B.V. All rights reserved.
Keywords: Coordination polymer; Imidazole; Crystal structure analysis; Crystal engineering; Topology
1. Introduction
ligands [12–16]. In this contribution, we illustrate the ease of
functionalisation of the imidazole group to yield three
structurally related ligands (Scheme 1), which have been
used to construct a range of interesting topologies.
Owing to their fascinating structural motifs and the promise
of new functional materials for diverse applications, coordi-
nation polymers have attracted significant attention over the
last two decades [1–5]. The formation of one-, two- and three-
dimensional frameworks relies on the use of ditopic or higher
ordered ligands and, in this context, pyridyl and carboxylate
functional groups are abundantly represented in the literature.
Considering their high affinity for metals and their relative ease
of functionalisation, imidazole functionalised ligands have
attracted surprisingly little attention to date [6]. Nevertheless,
the few existing examples of coordination polymers involving
imidazole derivatised ligands feature several interesting
structural motifs and topologies, which include polyrotaxanes,
pseudo-polyrotaxanes, two-dimensional Borromean frame-
works, poly-metallocage structures and adamantane-like 66
nets [7–13]. The overall objective of investigating the
formation of new topologies is to ultimately achieve the
rational design and construction of targeted coordination
networks. Indeed, some success has already been achieved
with the design of porous materials that utilize imidazole based
2. Experimental section
All commercially available chemicals were of reagent grade
and were used as received, without further purification. The
ligands 1,4-bis(2-methylimidazol-1-ylmethyl)benzene (1), 1,4-
bis(benzimidazol-1-ylmethyl)benzene (2) and 4,40-bis(benzi-
midazol-1-ylmethyl)biphenyl (3) were synthesised by the SN2
reaction of the imidazole moieties with the appropriate arenyl
dichloride spacer.
Single crystal X-ray diffraction data were recorded using a
Bruker SMART APEX diffractometer equipped with graphite-
˚
monochromated Mo Ka radiation (lZ0.71073 A). Empirical
absorption corrections were applied using SADABS [17].
Structures were solved using SHELXS 97 [18] and all ordered
non-hydrogen atoms were refined anisotropically by full-
matrix least-squares on F2 using SHELXL-97 under the X-Seed
environment [19–20]. Where feasible, hydrogen atoms were
either placed in calculated positions or located in difference
electron density maps. Crystal data are given in Table 1.
Hydrogen bond and coordination sphere geometric parameters
are available in supplementary material and CIF files. CCDC
reference numbers: 296902–296908. These data can be
obtained free of charge at www.ccdc.cam.ac.uk/conts/retriev-
ing.html (or from the Cambridge Crystallographic Data Centre,
*
Corresponding auhtor. Tel.: C27 21 808 3335; fax: C27 21 808 3849.
E-mail address: ljb@sun.ac.za (L.J. Barbour).
1 Permanent address: Faculty of Chemistry, Nicolaus Copernicus University,
´
Torun, Poland.
0022-2860/$ - see front matter q 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.02.059

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L. Dobrzanska et al. / Journal of Molecular Structure 796 (2006) 107–113
108
position and a nitrate anion disordered over two positions. The
copper cation is five-coordinate with square pyramidal
geometry defined by one apical water molecule and four
equatorial ligands 1. A one-dimensional coordination polymer
is formed parallel to [101] with ligand 1 assuming two
distinctive roles in connecting successive copper ions (Fig. 1).
One of the ligands is coordinated directly to two copper centres
by means of its two imidazole moieties (i.e. Cu–1–Cu). A
further two indirect Cu/Cu connections are present by virtue
of hydrogen bonded water bridges (i.e. Cu–H2O/H2O/1–
N
N
1
2
N
N
N
N
˚
N
N
Cu) (O(coordinated)/OZ2.775(5) A and O/NZ
˚
2.834(6) A) where each ligand is only coordinated to one
metal centre via one of its imidazole groups, while the
uncoordinated imidazole group accepts a hydrogen bond from
a lattice water molecule which, in turn, accepts a hydrogen
bond from a coordinated water molecule on an adjacent copper
ion. Taken together, the two indirect (/Cu–H2O/H2O/1–
Cu–H2O/H2O/1–) linkages can be thought of as a 34-
membered ring through, which the directly coordinated exo-
bidentate ligand is threaded and it may therefore be appropriate
to refer to this arrangement as a pseudo-polyrotaxane.
N
N
3
N
N
Scheme 1.
12, Union Road, Cambridge CB2 1EZ, UK; fax: C44 1223/
336 033; E-mail: deposit@ccdc.can.ac.uk).
3. Results and discussion
3.2. [Co(NCS)2(CH3OH)(1)1.5)]n (5)
3.1. [Cu(NO3)2(H2O)(1)1.5$4H2O]n (4)
Single crystals of 5 were obtained by slow evaporation of a
methanolic solution of CoCl2$6H2O, KSCN and 1 in a 1:2:4
molar ratio. The asymmetric unit consists of one Co2C cation,
one and a half ligands of 1, two thiocyanate counter ions and
one methanol molecule. The cobalt ion is in an octahedral
coordination environment consisting of three ligands of 1, two
N-coordinated thiocyanate anions and a coordinated methanol
molecule. Two ligands 1 are trans to one another and cis to the
Crystals suitable for X-ray diffraction analysis were
obtained by the reaction of Cu(NO3)2$3H2O with 1 (1:4
molar ratio) in MeOH, followed by slow evaporation of the
solvent. The asymmetric unit consists of a Cu2C ion and two
water molecules, all situated on a twofold rotation axis at 1/2, y,
3/4, one and a half ligands 1, one water molecule on a general
Table 1
Data collection and final refinement parameters for 4–10
4
5
6
7
8
9
10
Empirical formula
C48 H62 Cu
N14 O10
1058.66
100(2)
C27 H40 Co
N8 O S2
612.70
C25 H27 Ag
F3 N6 O3 S
656.46
100(2)
Trigonal
P-3
C44 H36 Cd
Cl2 N8
860.11
C20 H28 Cu
N4 O6
C26 H32 Cu
N4 O8
592.10
100(2)
C54 H56 Cu2
N7 O10
1090.14
100(2)
Formula weight
T (K)
484.01
298(2)
100(2)
100(2)
Crystal system
Space group
Monoclinic
C2/c
Monoclinic
P21/n
Monoclinic
P21/n
Monoclinic
P21/c
Monoclinic
P21/c
Monoclinic
C2/c
˚
a (A)
˚
b (A)
˚
c (A)
15.977(2)
12.4892(18)
25.713(4)
90
11.1229(8)
10.0174(7)
25.8715(18)
90
14.2551(11)
14.2551(11)
7.7890(12)
90
11.5035(14)
13.3651(16)
11.7868(14)
90
9.3730(10)
9.7008(10)
13.3403(14)
90
9.7515(16)
16.203(3)
17.360(3)
90
42.215(6)
15.666(2)
15.641(2)
90
a8
b8
g8
Z
100.952(3)
90
90.2590(10)
90
90
90.452(2)
90
107.908(2)
90
97.432(3)
90
100.354(3)
90
120
4
4
2
2
2
4
8
3
˚
V (A )
D (g/cm3)
5037.3(12)
1.396
2882.6(4)
1.419
1370.7(3)
1.590
1812.1(4)
1.576
1154.2(2)
1.393
2719.8(8)
1.446
10175(3)
1.423
Absorption coefficient (mmK1
)
0.506
0.777
0.870
0.797
0.988
0.859
0.902
Final R indices [IO2sigma(I)]:
R1, wR2
0.0749
0.0633
0.0551
0.0365
0.0430
0.1211
0.0821
0.2024
0.1130
0.2326
1.027
0.1458
0.0916
0.1601
1.040
0.1279
0.0630
0.1324
1.090
0.0815
0.0427
0.0843
1.036
0.1111
0.0538
0.1174
1.022
0.2816
0.1797
0.3244
1.051
0.1928
0.1276
0.2185
1.038
R indices (all data): R1, wR2
Goodness-of-fit on F2
K3
˚
Largest diff. peak and hole (e A
)
0.953
0.776
1.272
1.150
0.468
4.020
1.484
K0.569
K0.638
K0.951
K0.403
K0.197
K1.976
K0.566

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L. Dobrzanska et al. / Journal of Molecular Structure 796 (2006) 107–113
109
Fig. 1. Perspective view of the one-dimensional coordination polymer in 4. The 34-membered rings, each incorporating four hydrogen bonds, are shown in red.
These rings are threaded by directly coordinated ditopic ligands (yellow). All non-metal atoms are shown in capped-stick representation (for interpretation of the
reference to colour in this legend, the reader is referred to the web version of this article).
third ligand. Owing to this arrangement of the three ditopic
ligands, the metal centres act as three-connected nodes and a
two-dimensional (6,3) distorted honeycomb coordination net-
work is formed (Figs. 2 and 3) parallel to (101). The rings are
large and corrugated and thus result in the occurrence of
threefold parallel interpenetration (Fig. 3).
The approximately linear NCSK anions are both tilted with
respect to their respective Co–N vectors with Co–N–C angles
of ca. 1608. The coordinated methanol molecule is similarly
tilted with a Co–O–C angle of approximately 1258. One of the
thiocyanate sulphur atoms accepts a hydrogen bond from a
is BFK4 instead of CF3SOK3 . Although the overall topology of the
Borromean weave has already been described in detail, it is
interesting to now discuss the subtle influence exerted on the
structure by the anion. Both anions possess threefold rotation
symmetry, but the most obvious difference between them is
that the triflate anion is somewhat larger than the tetrafluor-
oborate anion. The most notable difference between the two
˚
structures is that the Ag/Ag separation in 6a is 3.0619(4) A
˚
while the corresponding distance in 6 is 3.225(1) A. Since the
anions are stacked in columns along [001], it is tempting to
presume that their stacking interval is responsible for the
adjustment of the argentophilic interactions. However, the
anions are not within van der Waals contact of one another
along [001] in either structure. In both structures, three
imidazole groups are situated about each silver ion in a
propeller-like fashion. Owing to steric effects, the imidazole
groups are required to rotate about the Ag–N vector such that
the methyl group of one imidazole moiety should be either
above or below the plane of the neighbouring imidazole ring.
In 6a, the methyl groups are oriented towards the outer surface
of the Borromean layer while they are oriented inwards in 6.
These two possible orientations of the imidazole rings about
the silver ion have a remarkable affect on the size of the
triangular cavity formed between the three components of the
˚
coordinated methanol hydroxyl group (S/OZ3.225 A) of
another (interpenetrated) layer and this relatively rare
hydrogen bond helps to bind the triply interpenetrated layers
to one another.
3.3. [Ag(1)(CF3SO3)]n (6)
Crystals were grown by slow evaporation of a methanolic
solution of 1 and Ag(CF3SO3) in a 1:1 molar ratio. X-ray
structural analysis reveals the formation of a Borromean weave
(Fig. 4) remarkably similar to that of a structure recently
reported by us ({[Ag213](BF4)2}, 6a) [10]. The only difference
in composition between 6 and 6a is that, in the latter, the anion
Fig. 2. Ball-and-stick perspective view of 5 showing six three-connected nodes that form the large rings of a (6,3) network.

´
L. Dobrzanska et al. / Journal of Molecular Structure 796 (2006) 107–113
110
Fig. 3. The parallel triple interpenetration of the two-dimensional (6,3) nets in 5. Individual nets, shown in red, yellow and blue, are idealised by representing the
metal/metal connection via ligand 1 as straight pipes (for interpretation of the reference to colour in this legend, the reader is referred to the web version of this
article).
Borromean weave (Fig. 5). When the methyl groups are
oriented outwards, the cavity becomes smaller and packing
interactions with smaller anions would thus favour this
conformation of the complex. However, enlargement of the
cavity by rotation of the imidazole ring such that the methyl
groups are directed inwards occurs at the expense of the Ag/
Ag interactions. Therefore, it appears that accommodation of
larger anions and the formation of stronger argentophilic
interactions are competing effects.
3.4. [CdCl2(2)2]n (7)
Crystals were grown from a solution of 2 in dichloro-
methane, layered with a solution of CdCl2$2.5H2O in
methanol. The asymmetric unit consists of a cadmium cation
situated on an inversion centre, one chloride anion and one
ligand 2. The cadmium ion is in an octahedral coordination
Fig. 4. Space filling representation of the infinite two-dimensional Borromean
weave in 6 projected along [001]. Each of the three components of the weave
consists of honeycomb lattices of ½Ag213ꢀN2C (shown as red, blue and yellow van
der Waals surfaces). The CF3SOK3 anions (green, capped-stick representation)
are situated in triangular lattice interstices (for interpretation of the reference to
colour in this legend, the reader is referred to the web version of this article).
Fig. 5. Perspective views of 6a (top) and 6 (bottom) along [001] showing the
triangular voids normally occupied by the anions, which have been omitted for
clarity. The size and shape of the void spaces are influenced by the orientations
of the 2-methyl groups (red) of the imidazole moieties (for interpretation of the
reference to colour in this legend, the reader is referred to the web version of
this article).

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L. Dobrzanska et al. / Journal of Molecular Structure 796 (2006) 107–113
111
adjacent layers associate only by means of van der Waals
interactions [21].
3.5. [Cu(CH3COO)2(1)2]n (8)
Crystals were grown by slow evaporation of 1 and
(CH3COO2)$H2O in a 3:2 molar ratio. X-ray analysis reveals
the formation of simple, symmetry-related one-dimensional
polymeric chains (Fig. 7) parallel to [1–10] and [110]. The
copper ion is in a square planar environment with two ligands 1
coordinated trans to one another (Table 2). The remaining two
coordination sites are occupied by monodentate acetate anions.
We presume that formation of the paddle–wheel arrangement
or bidentate coordination of acetate is sterically hindered by the
imidazole methyl groups. The non-coordinated oxygen atom of
the acetate ligand accepts a hydrogen bond from a water
molecule situated in the lattice. The water molecule also
donates a hydrogen bond to the coordinated acetate oxygen
atom of an adjacent one-dimensional strand. A series of one-
dimensional strands running parallel to [1–10] can be thought
of as forming a two-dimensional layer. The next layer along
[001] consists of one-dimensional strands running parallel to
[110] and thus adjacent layers of strands criss–cross one
another at an angle of approximately 928. Thus the hydrogen
bonded water bridges stitch adjacent layers to one another.
3.6. [Cu(CH3COO)2(H2O)(2)2$3H2O]n (9)
Crystals were obtained from a solution of 2 in chloroform,
layered with a solution of copper acetate monohydrate in
acetonitrile. The copper ion is in a square pyramidal
environment with two ditopic ligands 2 trans to one another
to yield a one-dimensional chain (Fig. 8 and Table 2). The
remaining trans coordination sites are occupied by two
monodentate acetate anions in a manner similar to that of 8.
A water molecule is coordinated to the apical site of the copper
ion. The square pyramids of adjacent metal centres are oriented
in an up–down fashion. All of the strands in the structure are
aligned parallel to [K101]. An extensive network of hydrogen
bonds serves to bind the strands together (Fig. 9). The
coordinated water molecule donates one hydrogen bond to a
water molecule situated in the lattice, which, in turn, donates
two hydrogen bonds to uncoordinated acetate oxygen atoms of
two separate chains. A second lattice water molecule donates a
hydrogen bond to one coordinated acetate oxygen atom as well
Fig. 6. Projections of 7 along [101] showing the formation of a two-dimensional
coordination polymer in capped-stick (top) and space filling representations
(bottom).
environment with two axial chloride ions and four ligands of 2
in equatorial positions. Two adjacent benzimidazole groups are
positioned with their benzo moieties on one side of the
equatorial plane while the remaining two benzo moieties are on
the other side of the plane. This alternative to a propeller-like
arrangement also serves to alleviate steric effects and a neutral
two-dimensional (4,4) net is formed (Fig. 6). The ligands
assume a conformation that occupies space efficiently and no
solvent molecules are present in the structure. Owing to the
abundance of aromatic groups, the two-dimensional layers are
dominated by edge-to-face p/p interactions although
Fig. 7. Capped-stick representation of the one-dimensional polymer in eight composed of square planar (shown in yellow) copper centres linked to one another by
ligand 1 (for interpretation of the reference to colour in this legend, the reader is referred to the web version of this article).

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L. Dobrzanska et al. / Journal of Molecular Structure 796 (2006) 107–113
112
Table 2
˚
Coordination geometric parameters for copper acetate structures 8, 9 and 10 (A, 8)
8
9
10-Cu(1)
10-Cu(2)
Cu(1)–N(3)#1 1.9756(18)
Cu(1)–N(3) 1.9756(18)
Cu(1)–O(1) 1.9928(17)
Cu(1)–O(1)#1 1.9928(17)
Cu(1)–N(3)#1 1.982(6)
Cu(1)–N(2) 1.991(6)
Cu(1)–O(2)#1 1.964(4)
Cu(1)–O(1) 1.971(4)
Cu(1)–O(3) 1.997(4)
Cu(1)–N(8) 2.137(4)
Cu(2)–O(5) 1.962(5)
Cu(2)–O(9) 1.978(5)
Cu(2)–N(1) 1.987(6)
Cu(2)–N(11) 1.990(5)
Cu(1)–O(8) 1.995(5)
Cu(1)–O(1) 1.995(6)
Cu(1)–O(5) 2.427(8)
N(3)#1–Cu(1)–N(3) 180.00(12)
N(3)#1–Cu(1)–O(1) 91.28(8)
N(3)–Cu(1)–O(1) 88.72(8)
N(3)#1–Cu(1)–N(2) 171.2(3)
N(3)#1–Cu(1)–O(8) 90.6(2)
N(2)–Cu(1)–O(8) 89.9(2)
N(3)#1–Cu(1)–O(1) 88.0(3)
N(2)–Cu(1)–O(1) 91.0(2)
O(8)–Cu(1)–O(1) 176.1(3)
N(3)#1–Cu(1)–O(5) 97.1(3)
N(2)–Cu(1)–O(5) 91.7(3)
O(8)–Cu(1)–O(5) 86.8(3)
O(1)–Cu(1)–O(5) 97.0(3)
O(2)#1–Cu(1)–O(1) 167.50(15)
O(2)#1–Cu(1)–O(4)#1 89.06(18)
O(1)–Cu(1)–O(4)#1 89.45(17)
O(2)#1–Cu(1)–O(3) 89.25(17)
O(1)–Cu(1)–O(3) 89.57(16)
O(5)–Cu(2)–O(9) 88.9(2)
O(5)–Cu(2)–N(1) 161.9(2)
O(9)–Cu(2)–N(1) 92.0(2)
O(5)–Cu(2)–N(11) 91.73(19)
O(9)–Cu(2)–N(11) 164.4(2)
N(1)–Cu(2)–N(11) 92.2(2)
N(3)#1–Cu(1)–O(1)#1 188.72(8)
N(3)–Cu(1)–O(1)#1 191.28(8)
O(1)–Cu(1)–O(1)#1 1180.00(9)
C(6)–O(1)–Cu(1) 103.98(14)
O(4)#1–Cu(1)–O(3) 167.73(16)
O(2)#1–Cu(1)–N(8) 100.34(16)
O(1)–Cu(1)–N(8) 92.16(16)
O(4)#1–Cu(1)–N(8) 98.46(16)
O(3)–Cu(1)–N(8) 93.79(16)
O(2)#1–Cu(1)–Cu(1)#1 85.10(11)
O(1)–Cu(1)–Cu(1)#1 82.41(11)
O(4)#1–Cu(1)–Cu(1)#1 85.17(12)
O(3)–Cu(1)–Cu(1)#1 82.58(11)
N(8)–Cu(1)–Cu(1)#1 173.47(12)
Cu(1) refers to the paddle–wheel coordination sphere and Cu(2) refers to the square planar coordination sphere of 10. Symmetry transformations used to generate
equivalent atoms for structure: 8: #1 xK1, KyC3/2, zC1/2 #2 xC1, KyC3/2, zK1/2; 9: #1 xK1, KyC3/2, zC1/2 #2 xC1, KyC3/2, zK1/2; 10: #1 KxC1/2, K
yC1/2, KzC2 #2 Kx, y, KzC1/2.
Fig. 8. Capped-stick representation of the one-dimensional molecular strand in 9. The copper cations are in a square pyramidal coordination environment (in yellow).
Successive square-based pyramids are canted at an angle of ca. 1358 relative to one another (for interpretation of the reference to colour in this legend, the reader is
referred to the web version of this article).
as to a third lattice water molecule. The latter donates a
hydrogen bond to a coordinated acetate oxygen atom and the
either donates or accepts a hydrogen bond to or from a
symmetry related instance of itself.
3.7. [Cu2(CH3COO)4(3)1.5$CH3CN$2CH3OH]n (10)
Crystals were prepared by the combination of equimolar
solutions of metal salt (copper acetate monohydrate in
acetonitrile) and ligand 3 (methanol), followed by diffusion
of ether into the mixture. X-ray analysis reveals the unusual
formation of one-dimensional strands containing two different
coordination geometries (Fig. 10). The well-known coordi-
nation of four acetate anions by two copper cations (i.e. the
paddle–wheel arrangement) occurs at one node (Table 2). The
apical positions of the two copper ions are each occupied by
benzimidazole groups of ligand 3. The other end of the ditopic
ligand is coordinated to a copper ion in a distorted square
planar environment (Table 2). Another ligand 3 is coordinated
to this metal in one of the cis positions while the other cis
position, as well as the trans position are occupied by
Fig. 9. Capped-stick representation of the hydrogen bonding network involving
water molecules in 9. A two-dimensional layer is formed. Contiguous hydrogen
bonded water tetramers are shown in yellow and the water molecules of
hydrogen bonded rings, which include non-coordinated acetate oxygen atoms,
are shown in blue. Ligand 2 has been omitted for clarity (for interpretation of
the reference to colour in this legend, the reader is referred to the web version of
this article).

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L. Dobrzanska et al. / Journal of Molecular Structure 796 (2006) 107–113
113
Fig. 10. Capped-stick representation of the one-dimensional coordination polymer of compound 10. Note that the paddle–wheel motif forms a linear coordination
node while the distorted square planar moiety forms a bent coordination node.
monodentate acetate anions. The other end of the cis ligand 3 is
coordinated to a symmetry-related instance of the square planar
copper ion, which is in turn linked via another ditopic ligand 3
to a paddle–wheel motif. The one-dimensional chain described
above forms an approximate sine wave parallel to [101] with
the paddle–wheel motifs situated on the horizontal axis of the
wave. At the square planar copper node, each of the non-
coordinated acetate oxygen atoms accepts a hydrogen bond
from a methanol solvent molecule situated in the lattice
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˚
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4. Conclusion
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can be synthesised with relative ease and functionalised with
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means of a variety of spacer groups. Owing to the versatile
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Financial support was provided by the National Research
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Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.molstruc.2006.02.059.