1D coordination polymers of silver(I) and copper(II) based on bis(N-heterocyclic carbene) ligands: Synthesis and structural studies

Article abstract of DOI:10.1016/j.poly.2010.03.025

The alkyl chain-linked diimidazolium (or dibenzimidazolium) salts, 1,1′-diethyl-4,4′-tetramethylene-diimidazolium-diiodide (L ¹H₂·I₂) and 1,1′-diethyl-3, 3′-trimethylene-dibenzimidazolium-diiodide (L²H ₂·I₂), and their silver(I) and copper(II) coordination polymers, [L¹AgI]_n (1) and [L ²Cu₂I₄]_n (2), have been prepared and characterized. Complex 1 is a 1D helical polymer generated by bidentated carbene ligands (L¹) and Ag(I) atoms. The 1D polymer of 2 is formed by bidentated carbene ligands (L²) and coplanar quadrilateral Cu ₂I₂ units. 3D supramolecular frameworks in the crystal packings of 1 and 2 are formed via intermolecular weak interactions, including C-H?π contacts, π-π interactions and C-H?I hydrogen bonds.

Full text of DOI:10.1016/j.poly.2010.03.025

Polyhedron 29 (2010) 2121–2126
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
1D coordination polymers of silver(I) and copper(II) based on
bis(N-heterocyclic carbene) ligands: Synthesis and structural studies
*
Qing-Xiang Liu , Meng-Chao Shi, Zhi-Qiang Wang, Shu-Wen Liu, Shu-Sheng Ge, Yan Zang,
Xiu-Guang Wang, Jian-Hua Guo
Tianjin Key Laboratory of Structure and Performance for Functional Molecule, College of Chemistry, Tianjin Normal University, Tianjin 300387, PR China
a r t i c l e i n f o
a b s t r a c t
Thealkyl chain-linkeddiimidazolium (ordibenzimidazolium) salts, 1,10-diethyl-4,40-tetramethylene-diim-
idazolium-diiodide (L1H2ꢀI2) and 1,10-diethyl-3,30-trimethylene-dibenzimidazolium-diiodide (L2H2ꢀI2),
and their silver(I) and copper(II) coordination polymers, [L1AgI]n (1) and [L2Cu2I4]n (2), have been prepared
and characterized. Complex 1 is a 1D helical polymer generated by bidentated carbene ligands (L1) and Ag(I)
atoms. The 1D polymer of 2 is formed by bidentated carbene ligands (L2) and coplanar quadrilateral Cu2I2
units. 3D supramolecular frameworks in the crystal packings of 1 and 2 are formed via intermolecular weak
Article history:
Received 3 March 2010
Accepted 31 March 2010
Available online 13 April 2010
Keywords:
Carbene polymer
Silver(I)
interactions, including C–Hꢀꢀꢀ
p
contacts,
p–
p
interactions and C–HꢀꢀꢀI hydrogen bonds.
Ó 2010 Elsevier Ltd. All rights reserved.
Copper(II)
Weak interactions
1. Introduction
reagents for synthesis and analysis were analytical grade and were
used without further purification. Melting points were determined
with a Boetius Block apparatus. 1H and 13C NMR spectra were re-
corded on a Varian Mercury Vx 400 spectrometer at 400 and
100 MHz, respectively. Chemical shifts, d, were reported in ppm
relative to the internal standard TMS for both 1H and 13C NMR.
J values are given in Hz. Elemental analysis was measured using
In the last two decades, complexes of N-heterocyclic carbenes
(NHCs) have experienced a rapid development and have been used
in many fields of chemistry [1]. In the family of NHCs, the options
for the NHC ring systems have been broadened, and a variety of
new NHCs based on imidazole, imidazolidine, benzimidazole, thia-
zole and benzothiazole have been prepared [2]. Because NHCs are
a
Perkin–Elmer 2400C Elemental Analyzer. The luminescent
strong
r
-donors, in some case, they have been found to be more
spectra were conducted on a Cary Eclipse Fluorescence spectro-
photometer. TGA curves were recorded on a Dupont thermal
analyzer.
effective ligands as organometallic catalysts than other two elec-
tron donor ligands such as phosphines [3]. Some NHC–metal com-
plexes have been applied to a broad spectrum of catalytic reactions
including C–C coupling reactions [4], olefin metathesis [5], hydro-
formylation [6] and CH-activation [7].
We are interested in developing bidentate bis-NHC ligands and
their metal complexes. Recently, several silver(I) and mercury(II)
complexes have been published by us [8]. We report herein the
synthesis and structural characterization of two new silver(I) and
copper(II) coordination polymers with flexible alkyl linkers,
[L1AgI]n (1) and [L2Cu2I4]n (2).
2.2. Preparation of L1H2ꢀI2
A THF solution of imidazole (14.980 g, 220 mmol) was added to
a suspension of oil-free sodium hydride (5.760 g, 240 mmol) in THF
(150 mL) and stirred for 1 h at 60 °C. A THF (100 mL) solution of
ethyl iodide (35.873 g, 230 mmol) was then added dropwise to
the above solution. The mixture was stirred for a further 48 h at
60 °C and a yellow solution was obtained. The solvent was re-
moved with a rotary evaporator and H2O (500 mL) was added to
the residue. The solution was the extracted with CH2Cl2
(3 ꢁ 100 mL), and the extracting solution was dried with anhy-
drous MgSO4. After removing CH2Cl2, 1-ethylimidazole was ob-
tained as a colorless oil by reduced-pressure distillation, the
fraction boiling at approximately 58–62 °C/5 mmHg. Yield:
11.845 g (56%). 1H NMR (400 MHZ, DMSO-d6): d 1.31 (t, J = 5.6,
3H, CH3), 3.87 (q, J = 5.6, 2H, CH2), 6.81 (s, 1H, 4 or 5-imiH), 6.91
(s, 1H, 4 or 5-imiH), 7.35 (s, 2H, 2-imiH) (imi = imidazole).
2. Experiment
2.1. General procedures
All manipulations were performed using Schlenk techniques,
and solvents were purified by standard procedures. All the
* Corresponding author. Tel.: +86 13820172297.
E-mail address: qxliu@eyou.com (Q.-X. Liu).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.03.025

2122
Q.-X. Liu et al. / Polyhedron 29 (2010) 2121–2126
A solution of 1-ethylimidazole (1.360 g, 14.2 mmol) and 1,4-
2.5. Preparation of [L2Cu2I4]n (2)
diiodobutane (2.000 g, 6.5 mmol) in 1,4-oxane (150 mL) was stir-
red for five days at 90 °C, and a pale yellow precipitate was formed.
The product was filtered and washed with acetone to give a pale
yellow powder of 1,10-diethyl-4,40-tetramethylene-diimidazoli-
um-diiodide (L1H2ꢀI2). Yield: 2.949 g (91%). M.p.: 126–128 °C. Anal.
Calc. for C14H24I2N4: C, 33.48; H, 4.82; N, 11.16. Found: C, 33.44; H,
4.78; N, 11.19%. 1H NMR (400 MHZ, DMSO-d6): d 1.44 (t, J = 5.6, 6H,
CH3), 1.84–1.90 (m, 4H, CH2), 4.45–4.49 (m, 8H, CH2), 7.38 (s, 2H, 4
or 5-imiH), 7.41 (s, 2H, 4 or 5-imiH), 9.48 (s, 2H, 2-imiH)
(imi = imidazole). 13C NMR (100 MHZ, DMSO-d6): d 15.4 (CH2CH3),
27.6 (CCH2C), 51.3 (NCH2C), 52.8 (NCH2C), 122.3 and 123.1 (4, 5-
imiC), 137.6 (NCHN).
A suspension of KOBut (0.090 g, 0.8 mmol), L2H2ꢀI2 (0.200 g,
0.3 mmol) and anhydrous copper(I) iodide (0.129 g, 0.7 mmol) in
THF (20 mL) and acetonitrile (20 mL) was refluxed for 48 h in air.
A brown solution was formed and the solvent was removed with
a rotary evaporator. Water (30 mL) was added to the residue, and
the solution was extracted with CH2Cl2 (3 ꢁ 20 mL). The extracting
solution was dried with anhydrous MgSO4, then the solution was
concentrated to 10 mL and hexane (5 mL) was added. This resulted
in a pale brown powder being obtained. Yield: 0.188 g (57%). M.p.:
160–162 °C. Anal. Calc. for C21H24Cu2I4N4: C, 26.08; H, 2.50; N, 5.79.
Found: C, 26.12; H, 2.53; N, 5.74%. 1H NMR (400 MHZ, DMSO-d6): d
1.48 (t, J = 5.6, 6H, CH3), 1.55 (m, 2H, CH2), 4.44–4.50 (m, 8H, CH2),
7.60-7.65 (m, 4H, PhH), 8.01–8.06 (m, 2H, PhH), 8.12–8.15 (m, 2H,
PhH). 13C NMR (100 MHZ, DMSO-d6): d 15.0 (CH2CH3), 30.3(CCH2C),
45.8 (NCH2C), 47.9 (NCH2C), 111.2, 112.5, 123.6, 124.2, 132.6 and
133.0 (PhC), 180.1(Ccarbene).
2.3. Preparation of L2H2ꢀI2
A THF solution of benzimidazole (2.000 g, 16.9 mmol) was
added to
a suspension of oil-free sodium hydride (0.480 g,
20.3 mmol) in THF (50 mL) and stirred for 1 h at 60 °C. A THF
(40 mL) solution of ethyl bromide (2.029 g, 18.6 mmol) was then
added dropwise to the above solution. The mixture was stirred
for a further 48 h at 60 °C and a yellow solution was obtained.
The solvent was removed with a rotary evaporator and H2O
(100 mL) was added to the residue. The solution was then ex-
tracted with CH2Cl2 (3 ꢁ 30 mL), and the extracting solution was
dried with anhydrous MgSO4. After removing CH2Cl2, the pale yel-
low liquid of 1-ethylbenzimidazole was obtained. Yield: 2.220 g
(90%).
2.6. X-ray structure determinations
For complexes 1 and 2, selected single crystals were mounted
on a Bruker SMART 1000 CCD diffractometer operating at 50 kV
and 20 mA using Mo K
a radiation (0.71073 Å). Data collection
Table 1
Crystal data and structure refinements for 1 and 2.
1
2ꢀH2O
A solution of 1-ethylbenzimidazole (2.922 g, 20.0 mmol) and
1,3-dibromopropane (2.019 g, 10.0 mmol) in THF (150 mL) was
stirred for three days under reflux, and a white precipitate was
formed. The product was filtered and washed with THF. A powder
Chemical formula
Formula weight
Crystal system
Space group
a (Å)
C
14H22AgIN4
C21H24Cu2I4N4ꢀH2O
481.13
orthorhombic
Pna21
18.097(2)
9.036(1)
10.826(1)
90
985.14
triclinic
ꢀ
P1
1,10-diethyl-3,30-trimethylene-dibenzimidazolium-dibromide
10.370(1)
12.415(1)
13.981(1)
75.7(2)
69.3(2)
74.7(2)
1601.9(3)
2
of
b (Å)
c (Å)
was obtained. Yield: 4.211 g (85%). M.p.: 176–178 °C.
NaI (3.640 g, 24.3 mmol) was added to a methanol solution of
a
(°)
1,10-diethyl-3,30-trimethylene-dibenzimidazolium
dibromide
b (°)
90
(4.000 g, 8.1 mmol) with stirring, and a white precipitate formed.
The product was collected by filtration, washed with small por-
tions of methanol, and dried in a vacuum to give the compound
L2H2ꢀI2. Yield: 4.230 g (88%). M.p.: 244–226 °C. Anal. Calc. for
c
(°)
90
1770.5(3)
4
1.805
2.879
V (Å3)
Z
Dcalc (Mg/m3)
2.047
5.200
920
Absorption coefficient (mmꢂ1
F(0 00 )
)
C21H26I2N4: C, 42.88; H, 4.46; N, 9.52. Found: C, 42.91; H, 4.50;
936
N, 9.48%. 1H NMR (400 MHZ, DMSO-d6): d 1.46 (t, J = 5.6, 6H,
CH3), 1.56 (m, 2H, CH2), 4.48–4.52 (m, 8H, CH2), 7.67–7.71 (m,
4H, PhH), 8.06–8.10 (m, 2H, PhH), 8.10–8.13 (m, 2H, PhH), 9.66
(s, 2H, 2-benzimiH) (benzimi = benzimidazole). 13C NMR
(100 MHZ, DMSO-d6): d 14.3 (CH2CH3), 31.2 (CCH2C), 46.4 (NCH2C),
47.5 (NCH2C), 112.8, 113.6, 122.7, 123.8, 131.5 and 132.2 (PhC),
138.9 (NCHN).
Crystal size (mm)
hminimum, hmaximum, (°)
T (K)
Number of data collected
Number of unique data
0.24 ꢁ 0.20 ꢁ 0.14
2.25, 25.03
296(2)
8610
2891
181
0.24 ꢁ 0.20 ꢁ 0.18
1.58, 25.01
296(2)
8019
5604
319
Number of refined parameters
Goodness-of-fit (GOF) on F2a
1.062
1.073
Final R indicesb [I > 2
r(I)]
R1
wR2
0.0517
0.1458
0.0665
0.2052
R indices (all data)
R1
wR2
2.4. Preparation of [L1AgI]n (1)
0.0749
0.1648
0.0751
0.2122
A suspension of L1H2ꢀI2 (0.200 g, 0.4 mmol) and silver oxide
(0.093 g, 0.4 mmol) in dichloromethane (30 mL) was refluxed un-
der nitrogen for 24 h. The resulting solution was filtered and con-
centrated to 5 mL, and Et2O (5 mL) was added to precipitate a
white powder. Isolation by filtration yielded [L1AgI]n (1). Yield:
0.113 g (59%). M.p.: 258–260 °C. Anal. Calc. for C14H22AgIN4: C,
34.95; H, 4.61; N, 11.65. Found: C, 34.91; H, 4.64; N, 11.62%. 1H
NMR (400 MHZ, DMSO-d6): d 1.44 (t, J = 5.6, 6H, CH3), 1.83–1.88
(m, 4H, CH2), 4.45–4.50 (m, 8H, CH2), 7.38 (s, 2H, 4 or 5-imiH),
7.41 (s, 2H, 4 or 5-imiH) (imi = imidazole). 13C NMR (100 MHZ,
DMSO-d6): d 16.1 (CH2CH3), 28.1 (CCH2C), 50.2 (NCH2C), 53.3
(NCH2C), 121.5 and 122.2 (4, 5-imiC). The carbene carbon was
not observed.
a
2
2 2
GOF = [
R
x
(Fo ꢂ Fc
)
/(n ꢂ p)]1/2, where n is the number of reflection and p is
the number of parameters refined.
b
2
R1
=
R
(||Fo| ꢂ |Fc||)/
R
|Fo|; wR2 = [
R
[w(Fo ꢂ Fc2)2]/
R .
w(Fo2)2]1/2
Table 2
Selected bond lengths (Å) and angles (°) for 1 and 2.
1
Ag1–C5
2.112(1) C5–Ag1–C10 160.7(5) C10–Ag1–I1 104.4(3)
Ag1–C10 2.097(1) C5–Ag1–I1
94.7(3)
N1–C5–N2
103.7(1)
Ag1–I1
3.064(1)
2
Cu1–I1
Cu1–I2
Cu1–I4
2.869(1) Cu1–C7
2.881(1) Cu2–C19
2.740(1) I1–Cu1–I2
1.923(2) I1–Cu1–I4
1.989(2) C7–Cu1–I1
98.1(4)
125.2(6)
108.8(1)
99.0(4)
N1–C7–N2

Q.-X. Liu et al. / Polyhedron 29 (2010) 2121–2126
2123
and reduction were performed using SMART and SAINT software [9]
3. Result and discussion
with frames of 0.6° oscillation in the h range 1.8° < h < 25°. An
empirical absorption correction was applied using the SADABS pro-
gram [10]. The structures were solved by direct methods and all
non-hydrogen atoms were subjected to anisotropic refinement by
full-matrix least squares on F2 using the SHELXTL package [11]. All
hydrogen atoms were generated geometrically (C–H bond lengths
fixed at 0.96 Å), assigned appropriated isotropic thermal parame-
ters and included in structure factor calculations. Crystal data
and structure refinement, and selected bond lengths (Å) and angles
(°) for 1 and 2 are presented in Tables 1 and 2, respectively.
3.1. Synthetic strategy
The alkyl chain-linked diimidazolium (or dibenzimidazolium)
salts, 1,10-diethyl-4,40-tetramethylene-diimidazolium-diiodide
(L1H2ꢀI2) and 1,10-diethyl-3,30-trimethylene-dibenzimidazolium-
diiodide (L2H2ꢀI2) were prepared from imidazole (or benzimid-
azole) by stepwise alkylation with a haloalkane followed by a
dihaloalkane in sequence (Scheme 1). The precursors L1H2ꢀI2 and
L2H2ꢀI2 are stable to air and moisture, and are soluble in polar or-
ganic solvents such as dichloromethane, acetonitrile, methanol,
and are almost insoluble in diethyl ether and petroleum ether. In
the 1H NMR spectra of L1H2ꢀI2 and L2H2ꢀI2, the imidazolium (or
benzimidazolium) proton signals (NCHN) appear at d = 9.48 and
9.66 ppm, respectively, which are consistent with the chemical
shifts of known imidazolium (or benzimidazolium) salts [12].
L1h2ꢀi2 was treated with silver oxide to afford the complex
[L1AgI]n (1). The complex [L2Cu2I4]n (2) was prepared by the reac-
tion of L2H2ꢀI2 with CuI in the presence of KOBut in CH3CN/THF in
air (Scheme 2). Complexes 1 and 2 are soluble in DMSO and are
insoluble in diethyl ether and hydrocarbon solvents. These
complexes are stable in air. The formation of the metal carbene
complexes was confirmed by 1H and 13C NMR spectroscopy and
X-ray crystallography. Crystals of 1 and 2 suitable for X-ray diffrac-
tion were grown by slow diffusion of diethyl ether into their
DMSO/CH2Cl2 solutions. In the 1H NMR spectra of 1 and 2, the dis-
appearance of the resonances for the imidazolium (or benzimi-
dazolium) protons (NCHN) shows the formation of the expected
metal carbene complexes, and the chemical shifts of other hydro-
gens are similar to those of the corresponding precursors. In the
13C NMR spectra, the signal for the carbene carbon of 1 was not ob-
served. The absence of the carbene carbon resonance is not unu-
sual. This phenomenon has been reported for some NHC-silver
complexes, and the reason given for this is the fluxional behavior
(
)
4
(
)
I
I
NaH
EtBr
4
Et
N
N
N
Et
N
N
NH
N
N
Et
2I-
L1H2·I2
(
)
(1)
NaH
EtBr
3
Br
Br
(
)
3
Et
N
N
N
N Et
N
NH
N
N Et
2I-
L2H2·I2
(2) NaI
Scheme 1. Preparation of precursors L1H2ꢀI2 and L2H2ꢀI2.
N
N
N
Ag
I
N
N
Ag2O
Ag
I
L1H2·I2
N
N
I
Ag
N
n
1
I
I
N
N
I
Cu
I
Cu
N
N
CuI
air
I
L2H2·I2
I
I
N
N
Cu
I
I
Cu
I
N
N
2
Scheme 2. Preparation of polymers 1 and 2.
Fig. 1b. 1D helical structure of 1 viewed along the c axis. The irrelevant carbon,
nitrogen, iodine and hydrogen atoms have been omitted for clarity.
Fig. 1a. 1D polymer of 1. All hydrogen atoms have been omitted for clarity. Symm. Code: i: 2 ꢂ x, 1 - y, 0.5 + z.

2124
Q.-X. Liu et al. / Polyhedron 29 (2010) 2121–2126
carbene center is 103.7(1)°. The AgꢀꢀꢀAg separation of 6.902(5) Å
indicates no metal–metal interaction [14], and the AgꢀꢀꢀAgꢀꢀꢀAg
bond angle of three adjacent silver(I) atoms is 103.3(2)°. The diam-
eter of he helical hole is ca. 6.9–8.8 Å. In each NHC–Ag–NHC unit,
two NHC rings form a dihedral angle of 69.4(1)°, and two NHC
rings in
40.0(4)°. Analysis of the crystal packing of 1 reveals that a 3D
supramolecular architecture is formed via C–Hꢀꢀꢀ contacts with
angle of 143.9(6)°
a NHC–(CH2)4–NHC unit form a dihedral angle of
p
a Hꢀꢀꢀ
p
separation of 2.963(2) Å and a C–Hꢀꢀꢀ
p
[15] (Fig. 1c and Fig. 1d).
3.3. Crystal structure of polymer [L2Cu2I4]n (2)
A 1D polymeric chain of 2 is formed through bidentated carbene
L2, copper(II) and bridging iodine atoms, as shown in Fig. 2a. Each
copper(II) is coordinated by one carbene–carbon and three iodine
atoms (two bridging iodines and one non-bridging iodine), adopt-
ing a distorted tetrahedral geometry. Four coplanar atoms (Cu1,
Cu2, I1 and I2) form a quadrilateral Cu2I2 arrangement. The two
non-bridging iodine atoms lie on the same side of the quadrilateral
plane. The Cu-I bond distances are in the range of 2.740(1)–
2.869(1) Å, and the I–Cu–I bond angles vary from 98.1(4)° to
105.1(4)°. The CuꢀꢀꢀCu separation of 3.506(2) Å in each Cu2I2 unit
indicates a weak metal–metal interaction (van der Waals radii of
copper = 1.9 Å). The Cu–C distances are 1.923(2) and 1.989(2) Å,
and the C–Cu–I bond angles vary from 112.6(7)° to 125.2(6)°.
The internal ring angle (N–C–N) at the carbene center is
108.8(1)°. These values are comparable to known NHC-copper
complexes [12d,12e]. In the polymeric chain, all benzimidazole
rings on the same side are parallel, and the benzimidazole rings
of both sides form a dihedral angle of 75.1(1)°. Additionally, all
quadrilateral Cu2I2 units in the polymeric chain are parallel, and
they form dihedral angles of 43.2(8)° and 46.4(8)° with the benz-
imidazole rings on either side. An interesting feature in the crystal
packing of 2 is that 3D supramolecular frameworks are formed
Fig. 1c. 3D supramolecular architecture of
1
formed via C–Hꢀꢀꢀ
p
contacts. All
hydrogen atoms except those participating in the C–Hꢀꢀꢀ
p contacts have been
omitted for clarity.
through p–p stacking interactions from benzimidazole rings with
a face-to-face separation of 3.550(1) Å (center-to-center separa-
tion = 3.684(1) Å) [16] and C–HꢀꢀꢀI hydrogen bonds (HꢀꢀꢀI dis-
tance = 2.985(8) Å, and C–HꢀꢀꢀI angle = 148.2(8)°) [17] (Fig. 2b and
Fig. 2c).
Fig. 1d. A portion view of 1 concerning C–Hꢀꢀꢀ
p contacts. All hydrogen atoms except
those participating in the C–Hꢀꢀꢀ contacts have been omitted for clarity.
p
of the NHCs complexes [13]. The signal for the carbene carbon of
complex 2 appears at d 180.1 ppm, which is consistent with the
chemical shifts of other known NHC–metal complexes [12].
3.4. Fluorescent emission spectra of L1H2ꢀI2, L2H2ꢀI2, 1 and 2
As shown in Fig. 3, fluorescent emission spectra of L1H2ꢀI2,
L2H2ꢀI2, 1 and 2 in the solid state are obtained upon excitation at
235 nm. The precursor L1H2ꢀI2 shows weak broad emission bands
in the region of 400–550 nm, and L2H2ꢀI2 exhibits an intense emis-
sion band centered at 425 nm, which correspond to intraligand
transitions. Complex 1 shows broad emission bands centered at
545 nm, which may be assigned to metal-centered electronic tran-
sitions [18]. Complex 2 exhibits double emission bands, and the
first emission band centered at 425 nm should originate from cop-
per(II) perturbed intraligand processes. The second emission band
centered at 500 nm may be assigned to metal-centered electronic
3.2. Crystal structure of polymer [L1AgI]n (1)
An interesting 1D helical polymer is obtained for 1 (Fig. 1a and
Fig. 1b), in which each silver(I) center is three-coordinated with
two carbene carbons and an iodine atom. The Ag–C bond distances
are 2.097(1) and 2.112(1) Å, and the Ag1–I1 bond distance is
3.064(1) Å. The C–Ag–C array (bond angle = 160.7(5)°) is not linear
due to the effect of the iodide ligand. The two C–Ag–I bond angles
are 104.4(3) and 94.70(3)°. The internal ring angle (N–C–N) at the
Fig. 2a. 1D polymer of 2. All hydrogen atoms have been omitted for clarity. Symm. Code: i: ꢂ1 + x, y, z.

Q.-X. Liu et al. / Polyhedron 29 (2010) 2121–2126
2125
3.5. Thermogravimetric analysis of complexes 1 and 2
Complexes 1 and 2 are air stable under ambient conditions, and
thermogravimetric experiments were performed to explore their
thermal stabilities. The TGA curve of 1 reveals that the complex
starts to decompose beyond 295 °C with two steps of weight losses
(peaks at 355.8 and 395.0 °C), and does not stop until heating ends
at 800 °C. The TGA curve of 2 suggests that the first weight loss of
2.10% in the region 115–150 °C (peaking at 130 °C) is corresponds
to the expulsion of lattice water molecules (calculated: 1.83%). The
starting decomposition of the residuary section occurs at 190 °C
with three steps of weight losses (peaks at 241, 258 and 395 °C)
and does not stop until heating ends at 800 °C.
4. Conclusion
In summary, two N-heterocyclic carbene Ag(I) and Cu(II) 1D
coordination polymers have been synthesised and characterized.
In the crystal packing of 1 and 2, weak intermolecular interactions
Fig. 2b. 3D supramolecular framework of 2 formed via
pꢀꢀꢀp interactions from
benzimidazole rings and C–HꢀꢀꢀI hydrogen bonds. All hydrogen atoms except those
participating in the C–HꢀꢀꢀI hydrogen bonds have been omitted for clarity.
exist, such as C–Hꢀꢀꢀ
p contacts, p–p stacking interactions and C–
HꢀꢀꢀI hydrogen bonds. These weak interactions are helpful in form-
ing 3D supramolecular frameworks. The NHC-silver(I) complex 1 is
stable toward light and air in the solid state at room temperature,
which may make it a convenient carbene precursor for the prepa-
ration of other transition metal complexes. The resultant struc-
tures of complexes 1 and 2 provide interesting experimental data
for supramolecular chemistry and crystal engineering. Further
studies on new organometallic compounds from the precursors
and analogous ligands are underway.
5. Supplementary data
CCDC 750941 and 750939 contain the supplementary crystallo-
graphic data for 1 and 2. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Center, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail:
deposit@ccdc.cam.ac.uk.
Fig. 2c. A portion view of 2 concerning
bonds. All hydrogen atoms except those participating in the C–HꢀꢀꢀI hydrogen bonds
have been omitted for clarity. Symm. Code: ii: ꢂ3 + x, y, 1 + z; iii: ꢂ3 + x, 1 + y, 1 + z.
pꢀꢀꢀp interactions and C–HꢀꢀꢀI hydrogen
Acknowledgements
L2H2I2
This work was financially supported by the National Science
Foundation of China (Project Grant No. 20872111) and the Natural
Science Foundation of Tianjin (07JCYBJC00300).
100000
80000
2
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