A series of 2D coordination complexes constructed from a flexible bis(methylbenzimidazole) ligand and different dicarboxylates

Article abstract of DOI:10.1016/j.ica.2012.07.033

Five coordination complexes [Cd(hbmb)(tbi)]_n (1), [Cd(hbmb)(adi)]_n (2), [Zn(hbmb)_0.5(atda)]_n (3), {[Zn₂(hbmb)(suc)_1.5(OH)]·2H₂O} _n (4), and {[Zn₂(hbmb) (fum)_1.5(OH)] ·2H₂O}_n (5) (H₂tbi = 5-tert-butylisophthalic acid, H₂adi = adipic acid, H₂atda = 1,3-adamantanediacetic acid, H₂suc = succinic acid, H ₂fum = fumaric acid, hbmb = 1,1′-(1,6-hexane)bis-(2- methylbenzimidazole)) have been hydrothermally synthesized and structurally characterized. Complex 1 is an undulated 2D structure with (6³) ₂ topology, containing left- and right-handed helical chains. Complex 2 possesses a puckered two-dimensional (2D) network with 4⁴· 6² topologies symbol. Complex 3 exhibits a 2D (4, 4) parallelogram network and also owns left- and right-handed helical chains. Complexes 4 and 5 display 2D rectangular grids and can be simplified as a four-connected 4 ⁴·6² topological network. Moreover, the photoluminescence properties and thermal stabilities of the five complexes were investigated.

Full text of DOI:10.1016/j.ica.2012.07.033

Inorganica Chimica Acta 403 (2013) 25–34
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
A series of 2D coordination complexes constructed from a flexible
bis(methylbenzimidazole) ligand and different dicarboxylates
⇑
Lu Liu, Yanhua Liu, Gang Han, Dongqing Wu, Hongwei Hou , Yaoting Fan
Department of Chemistry, Zhengzhou University, Zhengzhou 450052, Henan, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 13 August 2012
Five coordination complexes [Cd(hbmb)(tbi)]n (1), [Cd(hbmb)(adi)]n (2), [Zn(hbmb)0.5(atda)]n (3), {[Zn2
(hbmb)(suc)1.5(OH)]ꢀ2H2O}n (4), and {[Zn2(hbmb) (fum)1.5(OH)]ꢀ2H2O}n (5) (H2tbi = 5-tert-butylisophtha-
lic acid, H2adi = adipic acid, H2atda = 1,3-adamantanediacetic acid, H2suc = succinic acid, H2fum = fumaric
acid, hbmb = 1,10-(1,6-hexane)bis-(2-methylbenzimidazole)) have been hydrothermally synthesized and
structurally characterized. Complex 1 is an undulated 2D structure with (63)2 topology, containing left-
and right-handed helical chains. Complex 2 possesses a puckered two-dimensional (2D) network with
44ꢀ62 topologies symbol. Complex 3 exhibits a 2D (4, 4) parallelogram network and also owns left- and
right-handed helical chains. Complexes 4 and 5 display 2D rectangular grids and can be simplified as a
four-connected 44ꢀ62 topological network. Moreover, the photoluminescence properties and thermal sta-
bilities of the five complexes were investigated.
Coordination Polymers Special Issue
Keywords:
Cd(II) complexes
Zn(II) complexes
Crystal structure
Luminescence properties
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
when it coordinates to metal centers, and this often causes the
structural diversities [33–35]. In previous contributions, we have
Great attention in coordination complexes has been attracted
owing to their intriguing structural motifs and their potentials as
functional materials in catalysis, optics, magnetism, molecular
adsorption, molecular recognition, etc. [1–9]. The design of effective
ligands and the proper choice of metal centers are crucial to the con-
struction and structural tuning of the resulting complexes [10,11].
Although significant progress has been achieved in the design and
preparation of coordination complexes [12], it is still difficult to pre-
dict the exact structures of the final frameworks [13], because of the
fact that the crystallization process of coordination complexes de-
pends on various factors, such as the coordination nature of ligand,
the solvent systems, counterions, etc. [14,15]. Hence, further studies
on this topic are required for understanding the roles of these factors
in the formation of coordination complexes [13].
The employment of the ‘‘mix-ligand’’ synthetic strategies has
gradually become an effective method for the construction of coor-
dination complexes [16–22]. Up to now, polycarboxylate ligands
have been proven to be excellent structural constructors owing
to their diverse coordination modes to metal ions and the strong
coordinating ability of carboxylates [23–25]. On the other hand,
flexible ligands have been extensively used to construct metal
complexes [26–32]. Such ligands bearing alkyl spacers are a good
choice of N-donor ligands, and hold the energetic minimum, the
flexible nature of spacers allows the ligands to bend and rotate
reported lots of interesting structures based on flexible N-donor li-
gands 1,4-bis-(2-methylbenzimidazol-1-ylmethyl) benzene (bmb)
[36,37] and 1,4-bis(1,2,4-triazol-1-ylmethyl)-2,3,5,6-tetramethyl-
benzene (btmx) [38].
To further investigate the influence of flexibility and conforma-
tional freedom from a –CH2– spacer on the resultant structure of
complexes [39,40], we choose the longer flexible bis(methylbenzimi-
dazole) ligand hbmb (Scheme S1) as organic linker in the presence of
different dicarboxylates as coligands (Scheme S2) in this paper. Five
different structural coordination complexes, [Cd(hbmb)(tbi)]n (1),
[Cd(hbmb)(adi)]n (2), [Zn(hbmb)0.5(atda)]n (3), {[Zn2(hbmb)(suc)1.5
(OH)]ꢀ2H2O}n (4), and {[Zn2(hbmb) (fum)1.5(OH)]ꢀ2H2O}n (5) (H2tbi =
5-tert-butylisophthalic acid, H2adi = adipic acid, H2atda = 1,3-
adamantanediacetic acid, H2suc = succinic acid, H2fum = fumaric
acid, hbmb = 1,10-(1,6-hexane)bis-(2-methylbenzimidazole)) have
been obtained. Fluorescence and thermal stability have been carried
out on these complexes.
2. Experimental section
2.1. General information and materials
All reagents and solvents were commercially available except for
hbmb, which was synthesized according to the literature [41]. FT-IR
spectra were recorded on a Bruker-ALPHA spectrophotometer with
KBr pellets in 400–4000 cmꢁ1 region. Elemental analyses (C, H, and
N) were carried out on a FLASH EA 1112 elemental analyzer. Powder
⇑
Corresponding author. Tel./fax: +86 371 67761744.
E-mail address: houhongw@zzu.edu.cn (H. Hou).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.07.033

26
L. Liu et al. / Inorganica Chimica Acta 403 (2013) 25–34
X-ray diffraction (PXRD) patterns were recorded using Cu K
a1 radi-
2.3. Single-crystal X-ray diffraction measurements
ation on a PANalytical X’Pert PRO diffractometer. Thermal analyses
were performed on a Netzsch STA 449C thermal analyzer from room
temperature at a heating rate of 10 °C minꢁ1 in air. The lumines-
cence spectra for the powdered solid samples were measured at
room temperature on a Hitachi 850 fluorescence spectrophotome-
ter. The excitation slit and emission slit were both 2.0 nm.
All data were collected on a Rigaku Saturn 724 detector with
graphite monochromatic Mo Ka radiation (k = 0.71073 Å) at tem-
perature of 20 1 °C. Absorption corrections were applied by using
multi-scan program. The data were corrected for Lorentz and
polarization effects. The structures were solved by direct methods
and refined with a full-matrix least-squares technique based on F2
with the SHELXL-97 crystallographic software package [42]. All of the
non-hydrogen atoms were refined anisotropically. The hydrogen
atoms were assigned with common isotropic displacement factors
and included in the final refinement by using geometrical restrains.
Crystallographic crystal data and structure processing parameters
for 1–5 are summarized in Table 1. Selected bond lengths and bond
angles of 1–5 are listed in Table 2.
2.2. Synthesis
2.2.1. [Cd(hbmb)(tbi)]n (1)
A mixture of Cd(NO3)2ꢀ4H2O (0.2 mmol), hbmb (0.1 mmol),
H2tbi (0.2 mmol), NaOH (0.4 mmol) and H2O (8 mL) was placed in
a 25 mL Teflon-lined stainless steel container. The mixture was
sealed and heated at 160 °C for three days. After the mixture was
cooled to ambient temperature at a rate of 5 °C/h, colorless crystals
of 1 were obtained with a yield of 75% (based on Cd). Anal. Calc. for
C
34H38CdN4O4: C, 60.13, H, 5.64, N, 8.25. Found: C, 60.14, H, 5.63, N,
3. Results and discussion
8.27%. IR (KBr, cmꢁ1): 3451 (m), 3058 (w), 2955 (m), 1707 (w), 1608
(s), 1556 (s), 1415 (s), 1367 (s), 1272 (m), 1162 (w), 932 (w), 747 (s).
3.1. Structure description
3.1.1. Crystal structure of complex 1
2.2.2. [Cd(hbmb)(adi)]n (2)
Single crystal X-ray diffraction analysis shows that 1 crystallizes
in the acentric orthorhombic space group Pna21 which belongs to
the crystal class mm2, where optical activity can occur as specific
physical effects [46]. As shown in Fig. 1a, Cd1(II) ion adopts a dis-
torted octahedral coordination environment [47,48], defined by
four oxygen atoms from two tbi2ꢁ anions and two nitrogen atoms
from two hbmb. It can be clearly seen that the Cd2 atom is five
coordinated by three oxygen atoms from two tbi2- anions and
two nitrogen atoms from two hbmb, taking a distorted square-
A mixture of Cd(NO3)2ꢀ4H2O (0.2 mmol), hbmb (0.1 mmol),
H2adi (0.2 mmol), NaOH (0.4 mmol) and H2O (8 mL) was placed
in a 25 mL Teflon-lined stainless steel container. The mixture was
sealed and heated at 150 °C for three days. After the mixture was
cooled to ambient temperature at a rate of 5 °C/h, colorless crystals
of 2 were obtained with a yield of 70% (based on Cd). Anal. Calc. for
C
28H34CdN4O4: C, 55.77; H, 5.68; N, 9.29. Found: C, 55.76; H, 5.69;
N, 9.30%. IR (KBr, cmꢁ1): 3422 (w), 3060 (m), 2951 (m), 2860 (m),
1555 (s), 1412 (s), 1304 (m), 1237 (m), 1121 (w), 1013 (w), 928
(w), 852 (w), 759 (s).
pyramidal geometry (s = 0.13) [49,50]. The distances of Cd–O/N
bond range from 2.177(7) to 2.572(8) Å, which are similar to other
Cd-based complexes [51]. Interestingly, there are two kinds of
independent tbi2ꢁ. Two carboxylate groups of one kind of tbi2ꢁ an-
ions both adopt bisdentate chelated coordination mode. The other
2.2.3. [Zn(hbmb)0.5(atda)]n (3)
A mixture of Zn(Ac)2ꢀ2H2O (0.2 mmol), hbmb (0.1 mmol), H2atda
(0.2 mmol), and NaOH (0.2 mmol) in H2O (10 mL) was kept in a
25 mL Teflon-lined stainless steel vessel at 160 °C for three days.
After the mixture was cooled to room temperature at a rate of
5 °C/h, colorless crystals suitable for X-ray diffraction were obtained
with a yield of 65% (based on Zn). Anal. Calc. for C25H31N2O4Zn: C,
61.41; H, 6.39; N, 5.72. Found: C, 61.42; H, 6.39; N, 5.71%. IR (KBr,
cmꢁ1): 3426 (w), 3060 (w), 2925 (s), 2894 (s), 2846 (m), 1591 (s),
1408 (s), 1298 (m), 1239 (w), 1158 (w), 1016 (w), 942 (w), 755 (s).
kind of tbi2ꢁ anions act as a
l2-bridge, in which one carboxylate
group adopts a bidentate chelate mode and the other adopts a
monodentate coordination mode. Two kinds of tbi2ꢁ anions are
connected by Cd(II) atoms alternately giving rise to a 1D zigzag
chain (Fig. 1b). The hbmb ligand adopts asymmetric trans-confor-
mation with two different Ndonorꢀ ꢀ ꢀN–Csp3ꢀ ꢀ ꢀCsp3 torsion angles of
71.406° and 97.303°, bridging two Cd(II) atoms forming a 21-mem-
bered rings (Fig. 1c). The 1D chains containing 21-membered rings
are further extended by hbmb ligands into a 2D layer structure
(Fig. 1d). The hbmb ligand linking the 1D chains also adopts asym-
metric trans-conformation with two different Ndonorꢀ ꢀ ꢀN–Csp3-
ꢀ ꢀ ꢀCsp3 torsion angles of 77.056° and 88.484°, and the bridged
2.2.4. {[Zn2(hbmb)(suc)1.5(OH)]ꢀ2H2O}n (4)
A mixture of Zn(Ac)2ꢀ2H2O (0.2 mmol), hbmb (0.1 mmol), H2suc
(0.2 mmol), and NaOH (0.4 mmol) in H2O (8 mL) was kept in a
25 mL Teflon-lined stainless steel vessel at 160 °C for three days.
After the mixture was cooled to room temperature at a rate of
5 °C/h, colorless crystals of 4 were obtained with a yield of 80%
(based on Zn). Anal. Calc. for C14H18N2O4.5 Zn: C, 47.74; H, 5.29;
N, 7.95. Found: C, 47.75; H, 5.29; N, 7.94%. IR (KBr, cmꢁ1): 3438
(m), 3050 (w), 2929 (m), 2860 (w), 1578 (s), 1409 (s), 1014 (m),
936 (w), 806 (w), 754 (s).
Cdꢀ ꢀ ꢀCd distances along
l-hbmb are 13.1275 Å between two
adjacent 1D chains. It’s worth noting that 1 crystallizes in the non-
centrosymmetric polar space group Pna21. Accordingly, all bis-
methylbenzimidazole ligands are oriented in the same direction
[52–55], as shown in Fig. 1d. Interestingly, every two hbmb and
two tbi2- anions are alternately linked by adjacent Cd(II) ions to
form left- and right-handed helical chains. While the helical pitch
of left-handed helices is 17.9650(4) Å corresponding to the length
of b-axis, and the Cdꢀ ꢀ ꢀCd separation across tbi2ꢁ and hbmb bridge
is 9.2131 Å and 9.0227 Å, separately (Fig. 1e-left). The helical pitch
of right-handed helices is 19.2040(4) Å corresponding to the length
2.2.5. {[Zn2(hbmb) (fum)1.5(OH)]ꢀ2H2O}n (5)
The procedure is similar to that of 2, except that Zn(Ac)2ꢀ2H2O
was used instead of Cd(NO3)2ꢀ4H2O and H2fum was used instead
of H2adi. Yield, 50% (based on Zn). Anal. Calc. for C14H16.5N2O4.5Zn:
C, 47.94; H, 4.88; N, 7.98. Found: C, 47.93; H, 4.87; N, 7.97%. IR
(KBr, cmꢁ1): 3429 (m), 3052 (w), 2933 (w), 2860 (w), 1591 (s),
1460 (m), 1370 (s), 990 (w), 802 (w), 754 (m).
of c-axis, and the bridged Cdꢀ ꢀ ꢀCd distances along
l l-
-tbi2ꢁ and
hbmb are 9.2131 and 13.1275 Å, respectively (Fig. 1e-right).
As depicted in Fig. 1f, topological analysis is performed on 1. If
the Cd(II) ion were treated as a 3-connector. hbmb, tbi2ꢁ and 21-
membered rings are defined as linkers, respectively, the undulated
2D framework of 1 can be described as (63)2 topology.

L. Liu et al. / Inorganica Chimica Acta 403 (2013) 25–34
27
Table 1
Crystallographic data and structure refinement details for 1–5.
Complexes
1
2
3
4
5
Formula
Formula weight
T (K)
k (Mo K), (Å)
Crystal system
Space group
a (Å)
C
34H38CdN4O4
C28H34CdN4O4
602.99
293(2)
0.71073
Orthorhombic
Pbcn
9.2186(18)
17.128(3)
17.041(3)
90
C25H31N2O4Zn
488.89
293(2)
0.71073
Monoclinic
P21/c
10.836(2)
18.097(4)
11.340(2)
90
C28H37N4O9Zn2
704.40
293(2)
C28H34N4O9Zn2
701.37
293(2)
679.08
293(2)
0.71073
Orthorhombic
Pna21
19.072(4)
17.965(4)
19.204(4)
90
90
90
6580(2)
4
0.71073
0.71073
Triclinic
Triclinic
ꢀ
ꢀ
P1
P1
11.143(2)
12.284(3)
12.748(3)
69.85(3)
84.94(3)
72.46(3)
1561.8(5)
2
11.093(2)
12.359(3)
12.561(3)
70.98(3)
84.67(3)
71.61(3)
1544.8(6)
2
b (Å)
c (Å)
a
(°)
b (°)
90
90
2690.7(9)
4
92.98(3)
90
2220.9(8)
4
c
(°)
V (Å3)
Z
2hmax (°)
25.00
1.371
0.706
2800
25.00
1.489
0.852
1240
25.00
1.462
1.141
1028
25.00
1.496
1.592
728
25.00
1.495
1.609
712
Dcalc (g cmꢁ3
)
Absorption coefficient (mmꢁ1
F (000)
)
Reflections collected
Unique reflections
Rint
67437
11591
0.0937
1.121
0.0849
0.1995
0.00(5)
15287
2369
0.0474
1.024
0.0789
0.1877
–
23075
4127
0.0516
0.964
0.0554
0.1357
–
13153
5807
0.0367
0.904
0.0589
0.1619
–
15177
5400
0.0813
0.892
0.0856
0.2021
–
Goodness-of-fit (GOF)
R1 [I > 2
r
(I)]a
b
wR2 (all data)
Flack parameterc
a
b
c
R1 = ||Fo| – |Fc||/|Fo|.
wR2 = [w(|Fo2| – |Fc2|)2/w|Fo2|2]1/2. w = 1/[ 2(Fo)2 + 0.0297P2 + 27.5680P], where P = (Fo2 + 2Fc2)/3.
r
Absolute structure parameter [43–45].
3.1.2. Crystal structure of complex 2
Ndonorꢀ ꢀ ꢀN–Csp3ꢀ ꢀ ꢀCsp3 torsion angles of 91.916°. Ligand H2atda
adopts asymmetric trans-conformation.
When H2tbi was replaced by H2adi, a structurally different com-
plex 2 was obtained. The asymmetric unit of 2 consists of half of
Cd(II) ion, half of hbmb ligand, half of adi2ꢁ anion. As shown in
Fig. 2a, the Cd(II) ion adopts a distorted octahedral geometry via
coordinating with four oxygen atoms (O1, O2, O1A, O2A) from
two adi2ꢁ anions and two nitrogen atoms (N1 and N1A) from
two hbmb ligands. The Cd–O bond distances vary from 2.346(2)
to 2.3950(18) Å, while the Cd–N bond length is 2.2876(18) Å. They
are in conformity with those found in reported corresponding cad-
mium complexes [51]. hbmb adopts symmetric trans-conforma-
tion with the Ndonorꢀ ꢀ ꢀN–Csp3ꢀ ꢀ ꢀCsp3 torsion angle of 94.033°. The
adi2ꢁ anions adopt symmetric cis-conformation.
In 2, each hbmb ligand bridges two Cd(II) ions to generate a 1D
zigzag chain with a Cdꢀ ꢀ ꢀCd distance of 16.7491(18) Å along the a-
axis (Fig. 2b). The adi2ꢁ anions connect two adjacent Cd(II) ions
using its two carboxylate groups in a bisdentate chelated coordina-
tion mode, resulting in a 1D wave-like chain (Fig. 2c). The inter-
laced connection of Cd/hbmb and Cd/adi2ꢁ chains constructs the
2D network by sharing Cd(II) ions (Fig. 2d). A better insight into
such an elegant framework can be obtained by the topological ap-
proach (Fig. 2e). The Cd(II) ions can be simplified as 4-connected,
and hbmb and adi2ꢁ anions serve as linkers. Hence, the 2D network
of 2 can be described as a 4-connected topology with a point sym-
bol of 44ꢀ62.
In 3, two carboxylate groups of H2atda adopt different coordina-
tion modes: one carboxylate group adopts bidentate chelating
mode and the other adopts l2
anions act as 3-bridge linking Zn(II) ions to produce a one-dimen-
- : g
g1 1-bridging mode. The atda2ꢁ
l
sional (1D) double-chain structure having 8- and 20-membered
rings (Fig. 3b). The Znꢀ ꢀ ꢀZn distance is 3.8540 and 9.6667 Å in the
two types of rings, respectively. Such 1-D chains are further inter-
linked by flexible hbmb ligands to form a 2D layer (Fig. 3c). The
bridged Znꢀ ꢀ ꢀZn distance along
l-hbmb is 12.8278 Å. As exhibited
in Fig. 3d, every one hbmb and one H2atda are in turn connected by
Zn(II) ions to form left- and right-handed helical chains. Both of the
helical pitches are 11.340(2) Å corresponding to the length of c-
axis. From a topological perspective, if the [ZnC2O4]2 units are re-
garded as 4-connected nodes, and hbmb and atda2ꢁ anions are de-
fined as linkers, respectively, the 2D framework of 3 can be
described as 44ꢀ62 topology (Fig. 3e).
3.1.4. Crystal structure of complex 4 and complex 5
X-ray single crystal diffraction reveals that complexes 4 and 5
are isomorphous. Herein, only the structure of 4 is discussed in
ꢀ
detail. 4 crystallizes in the triclinic space group P1 and has two
crystallographically independent Zn(II) center. As shown in
Fig. 4a, Zn1 is five-coordinated, with a distorted square-pyramidal
geometry (s = 0.39) [49,50], by one nitrogen atom (N3) of one
3.1.3. Crystal structure of complex 3
hbmb ligand, three carboxylate oxygen atoms (O3, O4, O5) from
two suc2ꢁ anions, and one oxygen atom (O1) from one hydroxyl
group. However, the Zn2 atom adopts a distorted tetrahedral coor-
dination environment, defined by one nitrogen atom (N1) of one
hbmb ligand, two carboxylate oxygen atoms (O2, O7) from two
suc2ꢁ anions, and one oxygen atom (O1) from one hydroxyl group.
All the Zn–O and Zn–N bond lengths fall in the normal range except
that the Zn(2)–O(6) distance is 2.585(4) Å (Fig. 4a), suggesting a
non-negligible interaction with the uncoordinated carboxylate
Single crystal X-ray diffraction analysis reveals that 3 crystal-
lizes in monoclinic space group P21/c. As shown in Fig. 3a, each
Zn(II) atom is five-coordinated by one nitrogen atom (N1) from
one hbmb and four oxygen atoms (O1, O2, O3, O4) from three H2-
atda. The structural index parameter (s) [56] is 0.58, indicating that
the geometry around Zn(II) is best described as a trigonal bipyra-
midal distorted square-based pyramid (TBPDSBP) [56,57]. The
Zn–O distances are in the range of 1.968(3)–2.345(5) Å, while the
Zn–N bond length is 2.081(3) Å, which are in the normal range
[58]. hbmb adopts a symmetric trans-conformation with the
oxygen atom, which can be described as
coordination mode [59,60].
a semi-chelating

28
L. Liu et al. / Inorganica Chimica Acta 403 (2013) 25–34
Table 2
Selected bond lengths (Å) and bond angles (°) for 1–5.
Complex 1
Cd(1)–O(4)
Cd(1)–O(3)
Cd(2)–O(8)
Cd(2)–N(7)
O(4)–Cd(1)–N(1)
O(1)–Cd(1)–N(3)
O(1)–Cd(1)–O(2)
2.265(6)
2.487(7)
2.572(8)
2.278(8)
93.3(3)
Cd(1)–O(1)
Cd(2)–O(6)#1
Cd(1)–N(1)
2.272(7)
2.177(7)
2.301(8)
2.300(9)
111.5(3)
97.5(3)
Cd(1)–O(2)
Cd(2)–O(7)
Cd(1)–N(3)
O(4)–Cd(1)–O(1)
O(4)–Cd(1)–N(3)
O(4)–Cd(1)–O(2)
N(3)–Cd(1)–O(2)
2.459(7)
2.228(7)
2.313(9)
146.5(3)
96.2(3)
Cd(2)–N(5)
O(1)–Cd(1)–N(1)
N(1)–Cd(1)–N(3)
N(1)–Cd(1)–O(2)
102.2(3)
55.3(2)
101.0(2)
156.7(3)
97.1(3)
Complex 2
Cd(1)–N(1)
Cd(1)–O(2)#1
2.2876(18)
2.346(2)
96.20(9)
148.48(7)
116.41(6)
91.84(7)
91.84(7)
Cd(1)–N(1)#1
Cd(1)–O(1)#1
2.2876(18)
2.3950(18)
95.25(7)
95.25(7)
94.27(6)
94.27(6)
54.44(6)
Cd(1)–O(2)
Cd(1)–O(1)
2.346(2)
2.3950(17)
148.48(7)
90.06(10)
54.44(6)
116.41(6)
134.24(8)
N(1)–Cd(1)–N(1)#1
N(1)–Cd(1)–O(2)#1
N(1)–Cd(1)–O(1)#1
O(2)#1–Cd(1)–O(1)#1
O(2)–Cd(1)–O(1)
N(1)–Cd(1)–O(2)
N(1)#1–Cd(1)–O(2)#1
N(1)#1–Cd(1)–O(1)#1
N(1)–Cd(1)–O(1)
O(2)#1–Cd(1)–O(1)
N(1)#1–Cd(1)–O(2)
O(2)–Cd(1)–O(2)#1
O(2)–Cd(1)–O(1)#1
N(1)#1–Cd(1)–O(1)
O(1)#1–Cd(1)–O(1)
Complex 3
Zn(1)–O(3)
1.968(3)
Zn(1)–O(4)
1.976(3)
Zn(1)–O(2)
2.046(4)
Zn(1)–O(1)
2.345(5)
Zn(1)–N(1)
2.081(3)
O(3)–Zn(1)–O(4)
O(3)–Zn(1)–N(1)
O(3)–Zn(1)–O(1)
N(1)–Zn(1)–O(1)
120.01(13)
100.02(12)
97.95(16)
155.22(14)
O(3)–Zn(1)–O(2)
O(4)–Zn(1)–N(1)
O(4)–Zn(1)–O(1)
120.46(16)
95.33(12)
90.28(18)
O(4)–Zn(1)–O(2)
O(2)–Zn(1)–N(1)
O(2)–Zn(1)–O(1)
113.50(16)
99.13(14)
56.77(15)
Complex 4
Zn(1)–O(1)
1.914(4)
Zn(1)–O(3)
2.020(4)
Zn(2)–O(2)
2.017(4)
Zn(1)–O(5)
2.101(4)
Zn(1)–O(4)
2.304(5)
Zn(2)–O(1)
1.907(4)
Zn(2)–O(7)#1
O(1)–Zn(1)–O(3)
O(1)–Zn(1)–O(5)
O(1)–Zn(1)–O(4)
O(5)–Zn(1)–O(4)
O(7)#1–Zn(2)–N(1)
1.971(4)
Zn(2)–N(1)
2.016(4)
119.04(18)
90.2(2)
148.44(18)
122.13(19)
100.39(18)
Zn(1)–N(3)
2.024(4)
101.62(17)
124.69(19)
97.99(17)
58.22(18)
111.46(18)
O(1)–Zn(1)–N(3)
O(3)–Zn(1)–O(5)
O(3)–Zn(1)–O(4)
O(1)–Zn(2)–O(7)#1
O(1)–Zn(2)–O(2)
O(3)–Zn(1)–N(3)
N(3)–Zn(1)–O(5)
N(3)–Zn(1)–O(4)
O(1)–Zn(2)–N(1)
96.06(18)
112.90(19)
95.72(18)
120.90(17)
Complex 5
Zn(1)–O(1)
Zn(1)–O(4)
Zn(2)–O(5)#1
O(1)–Zn(1)–N(1)
O(1)–Zn(1)–O(4)
O(1)#1–Zn(2)–N(4)#2
O(1)#1–Zn(2)–O(6)
O(1)#1–Zn(2) –O(7)
1.9027(14)
2.0024(15)
2.0242(15)
119.52(7)
100.14(6)
119.17(7)
123.52(7)
95.86(6)
Zn(2)–O(6)
Zn(2)–O(1)#1
Zn(1)–N(1)
O(1)–Zn(1)–O(3)
N(1)–Zn(1)–O(4)
O(1)#1–Zn(2)–O(5)#1
N(4)#2–Zn(2)–O(6)
N(4)#2–Zn(2)–O(7)
2.0338(16)
1.9107(13)
1.9994(17)
126.83(7)
96.95(6)
102.70(6)
112.39(7)
94.83(7)
Zn(1)–O(3)
Zn(2)–O(7)
Zn(2)–N(4)#2
N(1)–Zn(1)–O(3)
O(3)–Zn(1)–O(4)
N(4)#2–Zn(2)–O(5)#1
O(5)#1–Zn(2)–O(6)
O(5)#1–Zn(2)–O(7)
2.0131(18)
2.4397(18)
2.0033(18)
109.06(7)
93.88(7)
97.90(7)
91.20(7)
148.55(6)
Symmetry transformations used to generate equivalent atoms:
for 1: #1 x,yꢁ1,z #2 ꢁx + 1,ꢁy + 1, zꢁ1/2 #3 ꢁx + 1, ꢁy + 1, z + 1/2 #4 x, y + 1, z.
for 2: #1ꢁx + 1, y, ꢁz + 1/2 #2 ꢁx, y, ꢁz + 1/2 #3 ꢁx + 2, ꢁy, ꢁz.
for 3: #1 ꢁx + 1, ꢁy + 2,ꢁz #2 ꢁx, ꢁy + 2, ꢁz #3 ꢁx, ꢁy + 2, ꢁz + 1.
for 4: #1 x + 1, y, z #2 ꢁx + 2, ꢁy + 1, ꢁz + 1 #3 ꢁx + 2,ꢁy + 2,ꢁz #4 xꢁ1, y, z.
for 5: #1 xꢁ1, y, z #2 ꢁx,ꢁy,ꢁz + 1 #3 ꢁx + 1,ꢁyꢁ1,ꢁz + 2 #4 x + 1, y, z.
In 4, trans-suc2ꢁ anions adopt different coordination modes: two
carboxylate groups of one kind of suc2ꢁ anions adopts bidentate and
monodentate chelating modes, respectively, as well as two carbox-
between neighboring imidazole rings and phenyl rings from benz-
imidazoles (Fig. 4f) [61].
ylate groups of the other kind of suc2ꢁ anions all adopts l2 g1 g1
- : -
3.2. Effects of hbmb and dicarboxylates on the structures of complexes
bridging mode. Each pair of Zn(II) ions is bridged by one carboxylate
group of suc2- anions and one oxygen atom from one coordinated
watermoleculeto producta dinuclearunit with a Znꢀ ꢀ ꢀZn separation
of 3.3035 Å. The dinuclear units [Zn2(CO2)O] are further extended by
suc2ꢁ anions into a 1D ladder chain along the c direction (Fig. 4b).
The 1D chains are further stacked by the linking of hbmb adopting
asymmetric cis-conformation with two different Ndonorꢀ ꢀ ꢀN–Csp3-
ꢀ ꢀ ꢀCsp3 torsion angles of 78.505° and 102.176°, thus leading to the
formation of a 2D framework (Fig. 4c-left). In addition, two hbmb li-
gands and two [Zn2(CO2)O] units construct a 30-membered rings
(Fig. 4c-right). The Znꢀ ꢀ ꢀZn distance across hbmb is 6.1026 Å. Topo-
logical analysis was carried out to get insight into the structure of 4.
If the dinuclear units [Zn2(CO2)O] is simplified as a 4-connected
node and the hbmb as well as the suc2ꢁ ligand are considered as link-
ers, the 2D rectangular grids can be described as a 44ꢀ62 topology
(Fig. 4d). Furthermore, the adjacent 2D layers are extended into a
1–5
Based on character of the flexible ligand, hbmb can exhibit cis/
trans-conformation and symmetric (with the same Ndonorꢀ ꢀ ꢀN–Csp3-
ꢀ ꢀ ꢀCsp3 torsion angles of two methylbenzimidazol arms)/asymmet-
ric (with different Ndonorꢀ ꢀ ꢀN–Csp3ꢀ ꢀ ꢀCsp3 torsion angles of two
methylbenzimidazol arms) conformations. From the structural
description above, hbmb presents asymmetric trans-conformation
in 1, symmetric trans-conformation in 2–3 and asymmetric cis-
conformation in 4–5. All of the NdonorꢀꢀꢀN-Csp3ꢀꢀꢀCsp3 torsion angles
are different in 1–5. The free conformations of -(CH2)- spacer
greatly enrich structures of complexes 1–5. In 1, hbmb bridges
adjacent Cd(II) ions leading to left-handed helices. At the same
time, hbmb and H2tbi are linked by adjacent Cd(II) ions forming
right-handed helices. In 2, each hbmb ligand bridges two Cd(II)
ions to generate a 1D zigzag chain. For 3, hbmb and H2atda are
in turn connected by Zn(II) ions to form left- and right-handed
helical chains. For 4, two hbmb ligands associate two [Zn2(CO2)O]
3D supramolecular framework (Fig. 4e) by the
p
ꢀ ꢀ ꢀ
p stacking
interactions with the centroid-to-centroid separation of 3.6168 Å

L. Liu et al. / Inorganica Chimica Acta 403 (2013) 25–34
29
Fig. 1. (a) Coordination environment of Cd (II) ion in 1 with hydrogen atoms omitted for clarity. (b) An infinite 1D zigzag chain constructed from Cd(II) centers and tbi2ꢁ
anions in 1. (c) The 1D chains containing 21-membered rings. (d) The 2D layer structure of 1 viewed along the a direction. (e) Views of the Cd(II)/hbmb/tbi2ꢁ left-handed
helical chain (left) and right-handed helical chain (right). (f) View of the undulating 2D network with (63)2 topology in 1.
units together to construct a 30-membered rings. Two bis(methyl-
benzimidazole) groups of hbmb can rotate freely when coordinat-
ing with central metal ions due to the flexible nature of the –
(CH2)– spacers, which leads to the different structure of complexes.

30
L. Liu et al. / Inorganica Chimica Acta 403 (2013) 25–34
Fig. 2. (a) Perspective view of the coordination environment of Cd(II) ion in 2 (hydrogen atoms are omitted for clarity). (b) The 1D zigzag chain constructed by Zn (II) ions and
hbmb. (c) The adi2ꢁ anions with cis-conformation link the adjoining Cd(II) ions into a 1D wave-like chain. (d) 2D layered structure of complex 2 (left) and schematic
representation of a 4-connected topology network with a point symbol of 44ꢀ62 (right).
In this work, we selected five dicarboxylates as auxiliary li-
gands. The carboxylate anions have great influence on building
the final structures of the complexes. In 1, each carboxylate group
of the rigid ligand H2tbi connects two Cd(II) atoms in bisdentate
chelated coordination mode giving rise to a 1D zigzag chain.
H2tbi together with hbmb links adjacent Cd(II) ions forming
right-handed helices. In 2, two carboxylate groups of adi2- anions,
which adopt symmetric cis-conformation in a bisdentate chelated
coordination mode, connect two adjacent Cd(II) ions forming a
beautiful 1D wave-like chain. When flexible H2atda was intro-
duced instead of the rigid ligand H2tbi, 3 was obtained. In 3, two
carboxylate groups of H2atda show two different coordination
modes: one adopts bidentate chelating mode and the other adopts
ylate coligands have an important effect on the features of resul-
tant complexes.
3.3. XRD results and thermal analyses
To confirm the phase purity of these complexes, the PXRD pat-
terns were recorded for complexes 1–5, and they were comparable
to the corresponding simulated ones calculated from the single-
crystal diffraction data (Fig. S1 in the Supporting Information),
indicating a pure phase of each bulky sample.
The thermal stabilities were investigated as shown in Fig. S2
(Supporting Information). The TGA curve of 1 shows a one step
weight loss process from 307 to 579 °C, corresponding to the decom-
position of organic components. A CdO residue of 20.65% (Calc.
18.91%) is observed. The framework of 2 remains intact until it is
heated to 292 °C, and the CdO residue of 22.56% (Calc. 21.30%) is ob-
tained at 634 °C. The TGA curve of complex 3 exhibits that it is stable
up to 352 °C and then loses weight from 352 to 582 °C, correspond-
ing to the decomposition of hbmb and atda2ꢁ. The remaining weight
l2- : g l3-bridge link-
g1 1-bridging mode. The atda2ꢁ anion acts as
ing Zn(II) ions to produce a 1D double-chain structure. Moreover,
H2atda alternately connects Zn(II) ions together with hbmb to form
left- and right-handed helical chains. For 4, suc2ꢁ anions in two
independent coordination modes bridge the [Zn2(CO2)O] units to
give rise to a 1D ladder chain. It can be observed that the dicarbox-

L. Liu et al. / Inorganica Chimica Acta 403 (2013) 25–34
31
Fig. 3. (a) Coordination environment of Zn (II) ion in 3 with hydrogen atoms omitted for clarity. (b) The 1D double-chain structure containing 8- and 20-membered rings. (c)
The 2D layer structure of 3 viewed along the b direction. (d) The Zn(II)/hbmb/atda2ꢁ left- and right-handed helical chains. (e) Schematic description of 2D parallelogram
network with 44ꢀ62 topology in 3.
corresponds to the formation of ZnO (obsd, 15.22%; Calc. 13.50%).
For 4, the TGA shows that the first weight loss of 5.36% in the range
of 65–112 °C is related to the loss of one lattice water molecule (Calc.
5.12%). The overall framework of 4 begins to decompose from 319 to

32
L. Liu et al. / Inorganica Chimica Acta 403 (2013) 25–34
Fig. 4. (a) Coordination environments of Zn(II) in complex 4 (hydrogen atoms are omitted for clarity). (b) The suc2ꢁ anions coordinate with Zn(II) ions to form a 1D ladder
chain along the c-axis. (c) 2D layered structure of complex 4 (left) and a 30-membered rings constructed by two hbmb ligands and two [Zn2(CO2)O] units (right). (d) The 2D
sheet consists of rectangular grids with 44ꢀ62 topology in 4. (e) Schematic view of 3D structure with water molecules in 4. (f) The illustration of
p–p interactions between two
neighboring layers (hydrogen atoms and the part of the structure are omitted for clarity).

L. Liu et al. / Inorganica Chimica Acta 403 (2013) 25–34
33
599 °C, corresponding to the losses of hydroxyl group and hbmb as
Acknowledgement
well as the decomposition of suc2ꢁ, and the ZnO residue of 23.94%
(Calc. 23.11%) is observed. Complex 5 shows a weight loss of 4.94%
from 59 to 139 °C corresponding to the release of lattice water
molecule (Calc. 5.14%), and then, a plateau region is observed.
The further weight loss is observed at about 312 °C due to the
decomposition of hydroxyl group and overall framework. A residue
of ZnO (obsd, 24.54%, Calc. 23.21%) is obtained at 567 °C.
We gratefully acknowledge the financial support by the Na-
tional Natural Science Foundation of China (Nos. 20971110 and
91022013).
Appendix A. Supplementary material
CCDC 881829, 881830, 881831, 881832, 881833 contains the
supplementary crystallographic data for complex 1, 2, 3, 4, 5. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ica.2012.07.033.
3.4. Luminescence properties
The coordination complexes with d10 metal centers have been
investigated for fluorescence properties owning to their potential
applications in photoactive materials [62–68]. Accordingly, the
emission spectra of Zn(II)/Cd(II) complexes 1–5, together with
the free hbmb ligand and all of the different dicarboxylic acids
were measured in the solid state at room temperature (Fig. S3 in
the Supporting Information). Under the same experimental condi-
tions, the emission intensities of H2adi, H2atda, H2suc, and H2fum
(Fig. S3a) are much weaker than that of N-donor ligand hbmb, so
it is considered that they have no significant contribution to the
fluorescent emission of the complexes with the presence of hbmb.
The free ligands hbmb and H2tbi show intense emissions bands at
306 nm (kex = 275 nm) and 319 nm (kex = 273 nm), respectively.
The solid state photoluminescence spectra of complexes 1–5 at
ambient temperature are depicted in Fig. S3b. It is clear that there
are emission bands at 445 nm (kex = 365 nm) for 1, 446 nm
(kex = 366 nm) for 2, 301 nm (kex = 276 nm) for 3, 309 nm
(kex = 284 nm) for 4, 442 nm (kex = 368 nm) for 5, respectively.
For complex 1, the emission band is highly red-shifted (139 and
126 nm) compared to the free hbmb and H2tbi, respectively. This
red shift may be tentatively assigned to ligand-to-metal charge
transfer (LMCT) character [69,70]. 1 has interesting dual emissions,
which may be ascribed to the different structural topology of 1
[71]. Obviously, the fluorescent emission bands of 3 and 4 can be
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