Construction of six coordination networks based on a flexible bis(methylbenzimidazole) ligand and isomeric benzenedicarboxylates

Article abstract of DOI:10.1016/j.ica.2012.04.043

To explore the influence of isomeric benzenedicarboxylates on the self-assembly of coordination frameworks, six mixed-ligands Zn(II)/Co(II) coordination complexes, [Zn(pbmb)(1,4-bdc)]_n (1), {[Co(pbmb)(1,4-bdc)]·1.5H₂O}_n (2), [M(pbmb)(1,3-bdc)]_n [M = Zn (3) or Co (4)], and [M(pbmb)(1,2-bdc)] _n [M = Zn (5) or Co (6)] (pbmb = 1,1′-(1,3-propane)bis-(2- methylbenzimidazole), 1,2-bdc = 1,2-benzenedicarboxylic acid, 1,3-bdc = 1,3-benzenedicarboxylic acid, and 1,4-bdc = 1,4-benzenedicarboxylic acid), have been obtained and structurally characterized. Structural analyses reveal that complexes 1 and 2 display 2D (4, 4) networks, of which complex 1 contains left- and right-handed helical chains arranged alternately and 2 owns a well-known paddle-wheel binuclear clusters. Complexes 3 and 4 feature 2D networks with 6³ topologies, and complexes 5 and 6 exhibit 1D double-chain structures. Additionally, complexes 1-6 present high thermal stabilities, as well as 1, 3, and 5 show different photoluminescence behaviors in the solid state.

Full text of DOI:10.1016/j.ica.2012.04.043

Inorganica Chimica Acta 391 (2012) 66–74
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Construction of six coordination networks based on a flexible
bis(methylbenzimidazole) ligand and isomeric benzenedicarboxylates
⇑
Lu Liu, Xiaoli Li, Chunying Xu, Gang Han, Ying Zhao, Hongwei Hou , Yaoting Fan
Department of Chemistry, Zhengzhou University, Zhengzhou, Henan 450052, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
To explore the influence of isomeric benzenedicarboxylates on the self-assembly of coordination frame-
works, six mixed-ligands Zn(II)/Co(II) coordination complexes, [Zn(pbmb)(1,4-bdc)]n (1), {[Co(pbmb)(1,
4-bdc)]ꢀ1.5H2O}n (2), [M(pbmb)(1,3-bdc)]n [M = Zn (3) or Co (4)], and [M(pbmb)(1,2-bdc)]n [M = Zn (5) or
Co (6)] (pbmb = 1,10-(1,3-propane)bis-(2-methylbenzimidazole), 1,2-bdc = 1,2-benzenedicarboxylic acid,
1,3-bdc = 1,3-benzenedicarboxylic acid, and 1,4-bdc = 1,4-benzenedicarboxylic acid), have been obtained
and structurally characterized. Structural analyses reveal that complexes 1 and 2 display 2D (4, 4) networks,
of which complex 1 contains left- and right-handed helical chains arranged alternately and 2 owns a well-
known paddle-wheel binuclear clusters. Complexes 3 and 4 feature 2D networks with 63 topologies, and
complexes 5 and 6 exhibit 1D double-chain structures. Additionally, complexes 1–6 present high thermal
stabilities, as well as 1, 3, and 5 show different photoluminescence behaviors in the solid state.
Ó 2012 Elsevier B.V. All rights reserved.
Received 20 January 2012
Received in revised form 16 April 2012
Accepted 24 April 2012
Available online 3 May 2012
Keywords:
N/O-containing ligands
Positional isomer
Co(II) complexes
Zn(II) complexes
Luminescence properties
1. Introduction
functional ligand. The spacers –CH2– allow the ligand to bend and
rotate when it coordinates with metal ions, which leads to different
To date, the design and construction of coordination networks
have been quickly developing because of their fascinating struc-
tural diversities and potential applications [1–7]. Researches in this
field have been concentrated on modifying the building blocks and
controlling the assembled motifs for required products via selecting
different organic ligands [8,9]. Therefore, selective design of organic
ligands are usually crucial for the formation of novel frameworks.
Flexible ligands containing N-donors [10–12], which possess rich
structural information and free conformation, are highly attractive
because their flexibilities allow for greater structural diversity [13–
20]. Among them, the flexible bis-imidazole/triazole/benzimid-
azole ligands, such as 1,10-(1,4-butanediyl)bis(imidazole) [21],
1,4-bis(imidazol-1-ylmethyl)benzene [22,23], 1,2-bis(1,2,4-tria-
zol-4-yl)ethane [24,25], 1,1-(1,4-butanediyl)bis-1H-benzimidazole
[26] have been widely reported. Some coordination complexes with
flexible ligands have shown interesting properties [27–29]. In our
previous works, we have reported lots of fascinating structures
based on semirigid N-donor ligand 1,4-bis-(2-methylbenzimida-
zol-1-ylmethyl)benzene [30,31] and 4,40-bis(1,2,4-triazol-1-
ylmethyl)biphenyl [32,33]. When spacers like methylene groups
are introduced between the two 2-methylbenzimidazole rings in-
stead of benzene ring, the resulting ligand acquires more flexibility
[34]. On the basis of above mentioned, we designed a ligand 1,10-
(1,3-propane)bis-(2-methylbenzimidazole) (pbmb) (Chart 1) as a
conformations and coordination modes [35,36].
In addition, the two-ligand assembly system is capable of pro-
viding more variability to build complicated and fascinating struc-
tures. Carboxylates acting as coligands have been extensively
adopted to construct new complexes [37–43]. The phenyl dicar-
boxylate isomers containing two carboxyl groups at distinct posi-
tions can engender significant spatial effect and influence the
structural assembly with multiform coordination fashions. There-
fore, multidentate O-donor organic aromatic carboxylate ligands,
1,2-benzenedicarboxylic acid (1,2-H2bdc), 1,3-benzenedicarboxy-
lic acid (1,3-H2bdc), and 1,4-benzenedicarboxylic acid (1,4-
H2bdc) are introduced into this paper, and six diverse complexes,
[Zn(pbmb)(1,4-bdc)]n (1), {[Co(pbmb)(1,4-bdc)]ꢀ1.5H2O}n (2), [M
(pbmb)(1,3-bdc)]n [M = Zn (3) and Co (4)], and [M(pbmb)(1,2-
bdc)]n [M = Zn (5) and Co (6)] were synthesized. The crystal struc-
ture analysis of these complexes, as well as the effect of different
aromatic carboxylates on the ultimate frameworks, are also repre-
sented and discussed. The structural differences demonstrate that
the backbones of the benzenedicarboxylates are key factors in for-
mation of the final coordination complexes.
2. Experimental
2.1. General information and materials
⇑
All chemicals were of A.R. Grade and used without further
purification. IR data were recorded on a BRUKER TENSOR 27
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.2012.04.043

L. Liu et al. / Inorganica Chimica Acta 391 (2012) 66–74
67
Teflon-lined stainless steel container and then stirred for 0.5 h. The
mixture was sealed and heated at 130 °C for three days. After the
mixture was cooled to ambient temperature at a rate of 5 °C/h,
the pale yellow crystals were obtained with a yield of 88% (based
on Zn). Anal. Calc. for C27H24ZnN4O4: C, 60.74; H, 4.53; N, 10.49.
Found: C, 60.73; H, 4.53; N, 10.50%. IR (KBr, cmꢁ1): 3362 (w),
2956 (w), 1691 (w), 1630 (s), 1460 (m), 1386 (m), 1340 (m),
1293 (m), 749 (s),716(w).
N
N
N
N
2.2.3. {[Co(pbmb)(1,4-bdc)]ꢀ1.5H2O}n (2)
The procedure is similar to that of 1, except that Co(NO3)2ꢀ6H2O
was used instead of Zn(NO3)2ꢀ6H2O. The dark purple crystals were
obtained with a yield of 65% (based on Co). Anal. Calc. for
Pbmb
C54H48Co2N8O11: C, 58.81; H, 4.38; N, 10.16. Found: C, 58.80; H,
4.39; N, 10.14%. IR (KBr, cmꢁ1): 2930 (w), 1609 (w), 1601 (s),
1450 (w), 1138 (w), 1391 (m), 1122 (w), 1134 (w), 752 (m).
Chart 1. The N-heterocyclic ligand adopted in this paper.
spectrophotometer with KBr pellets in 400–4000 cmꢁ1 region. Car-
bon, hydrogen and nitrogen analyses were carried out on a FLAS-
HEA 1112 elemental analyzer. Thermal analyses were performed
on a Netzsch STA 449C thermal analyzer from room temperature
at a heating rate of 10 °C minꢁ1 in air. Steady state fluorescence
measurements were performed using spectrofluorimeter Hitachi
F-4500 at ambient temperature in solid-state. The excitation and
emission slit width are both 5 nm, and response time is 0.5 s.
2.2.4. [Zn(pbmb)(1,3-bdc)]n (3)
The procedure is similar to that of 1, except that 1,3-H2bdc was
used instead of 1,4-H2bdc. Yield: 82% (based on Zn). Anal. Calc. for
C
27H24ZnN4O4: C, 60.74; H, 4.53; N, 10.49. Found: C, 60.75; H, 4.52;
N, 10.51%. IR (KBr, cmꢁ1): 3362 (w), 2932 (w), 1620 (s), 1594 (w),
1460 (m), 1375 (s), 1296 (w), 1154 (w), 761 (s), 702 (w).
2.2.5. [Co(pbmb)(1,3-bdc)]n (4)
2.2. Synthesis
The procedure is similar to that of 3, except that Co(NO3)2ꢀ6H2O
was used instead of Zn(NO3)2ꢀ6H2O. Yield: 90% (based on Co). Anal.
Calc. for C27H20CoN4O4: C, 61.95; H, 3.85; N, 10.70. Found: C, 61.96;
H, 3.83; N, 10.69%. IR (KBr, cmꢁ1): 2923 (w), 1709 (w), 1628 (s),
1460 (w), 1141 (w), 1384 (m), 1122 (w), 1151 (w), 748 (m).
2.2.1. 1,1’-(1,3-propane)bis-(2-methylbenzimidazole) (pbmb)
Ligand 1,10-(1,3-propane)bis-(2-methylbenzimidazole) (pbmb)
(Chart 1) was prepared according to the literature [44]. Anal. Calc.
for C19H20N4: C, 74.97; H, 6.62; N, 18.41. Found: C, 74.95; H, 6.60;
N, 18.39%. IR (KBr, cmꢁ1): 2361 (s), 2337 (s), 1740 (s), 1718 (s),
1677 (w), 1617 (w), 1520 (s), 1457 (s), 1411 (s), 1288 (m), 1219
(m), 1150 (w), 1012 (w), 734 (s), 670 (w), 531 (w).
2.2.6. [Zn(pbmb)(1,2-bdc)]n (5)
The procedure is similar to that of 1, except that 1,2-H2bdc was
used instead of 1,4-H2bdc. Yield: 50% (based on Zn). Anal. Calc. for
2.2.2. [Zn(pbmb)(1,4-bdc)]n (1)
C27H24ZnN4O4: C, 60.74; H, 4.53; N, 10.49. Found: C, 60.75; H, 4.52;
A mixture of pbmb (0.1 mmol), Zn(NO3)2ꢀ6H2O (0.1 mmol), 1,4-
N, 10.51%. IR (KBr, cmꢁ1): 1708 (w), 1617 (s), 1592 (m), 1569 (w),
1482 (w), 1375 (s), 1146 (w), 761 (m).
H2bdc (0.1 mmol) and 10 mL of distilled H2O was placed in a 25 mL
Table 1
Crystallographic data and structure refinement details for 1–6.
Complexes
1
2
3
4
5
6
Formula
Fw
T (K)
k(Mo K) (Å)
Crystal systems
Space group
a (Å)
C
27H24N4O4Zn
C54H48Co2N8O11
1102.86
293(2)
0.71073
orthorhombic
P2(1)/c
11.261(2)
16.412(3)
14.307(3)
90
C27H24N4O4Zn
533.87
293(2)
0.71073
monoclinic
P2(1)/n
11.491(2)
17.454(4)
12.621(3)
90
C27H24CoN4O4
527.43
293(2)
0.71073
monoclinic
P2(1)/n
11.512(2)
17.457(4)
12.642(3)
90
C27H24N4O4Zn
533.87
293(2)
0.71073
triclinic
C27H24CoN4O4
527.43
293(2)
0.71073
triclinic
266.94
293(2)
0.71073
orthorhombic
Pccn
ꢀ
ꢀ
P1
P1
17.237(3)
11.031(2)
12.413(3)
90
90
90
10.848(2)
11.268(2)
11.565(2)
65.41(3)
83.30(3)
67.56(3)
1186.6(4)
2
10.863(2)
11.288(2)
11.561(2)
65.19(3)
83.34(3)
67.74(3)
1189.3(4)
2
b (Å)
c (Å)
a
(°)
b (°)
90.00(3)
90
2644.0(9)
4
106.56(3)
90
2426.1(8)
4
106.48(3)
90
2436.2(8)
4
c
(°)
V (Å3)
2360.1(8)
8
Z
2hmax (°)
27.8804
1.502
1.084
25.00
1.405
0.697
27.97
1.462
1.054
29.15
1.438
0.746
27.88
1.494
1.078
24.99
1.473
0.764
Dcalc (g cmꢁ3
)
Absorbance coefficient (mmꢁ1
)
F(000)
1104
1156
1104
1092
552
546
Reflections collected
Unique reflections
R(int)
13359
2072
0.0319
1.173
0.0378
0.0831
26662
4664
0.0327
1.129
0.0535
0.1551
29375
5817
0.0646
1.172
0.0562
0.1377
32361
6543
0.0283
1.140
0.0429
0.1069
14832
5619
0.0274
1.065
0.0431
0.0968
11895
4166
0.0198
1.074
0.0312
0.0811
GOF
R1 [I > 2
r
(I)]a
wR2 (all data)b
a
R1 = |Fo ꢁ Fc|/Fo.
b
2
22
wR2 = [w(Fo ꢁ Fc2)2/wFo
]
1/2. w = 1/[ 2(Fo)2 + 0.0297P2 + 27.5680P], where P = (Fo2 + 2Fc2)/3.
r

68
L. Liu et al. / Inorganica Chimica Acta 391 (2012) 66–74
Table 2
Selected bond lengths (Å) and bond angles (°) for 1–6.
Complex 1
Zn(1)–O(1)
Zn(1)–N(1)
O(1)#1–Zn(1)–N(1)#1
N(1)#1–Zn(1)–N(1)
1.9575(17)
2.022(2)
103.77(8)
113.02(11)
Zn(1)–O(1)#1
O(1)–Zn(1)–O(1)#1
O(1)–Zn(1)–N(1)
1.9575(17)
112.41(11)
103.77(8)
Zn(1)–N(1)#1
O(1)–Zn(1)–N(1)#1
(1)#1–Zn(1)–N(1)
2.022(2)
112.08(8)
112.08(8)
Complex 2
Co(1)–O(3)#1
Co(1)–N(1)
O(3)#1–Co(1)–O(1)
O(3)#1–Co(1)–N(1)
1.9426(14)
2.0575(18)
114.71(7)
118.40(7)
Co(1)–O(1)
1.964(16)
2.056(16)
105.67(7)
105.43(7)
Co(1)–N(4)#2
O(3)–Co(1)#1
O(1)–Co(1)–N(4)#2
N(4)#2–Co(1)–N(1)
2.056(16)
1.943(14)
98.78(6)
N(4)–Co(1)#2
O(3)#1–Co(1)–N(4)#2
O(1)–Co(1)–N(1)
112.23(7)
Complex 3
Zn(1)–O(3)#1
Zn(1)–N(4)
O(1)–Zn(1)–N(1)
N(1)–Zn(1)–N(4)
1.937(2)
2.068(2)
101.91(10)
98.99(10)
Zn(1)–O(1)
O(3)#1–Zn(1)–O(1)
O(3)#1–Zn(1)–N(4)
1.944(2)
123.43(9)
100.26(10)
Zn(1)–N(1)
O(3)#1–Zn(1)–N(1)
O(1)–Zn(1)–N(4)
2.027(2)
121.67(10)
107.00(10)
Complex 4
Co(1)–O(3)#1
Co(1)–N(3)
(1)–Co(1)–N(1)
N(1)–Co(1)–N(3)
1.9410(15)
2.0616(15)
102.01(6)
99.47(6)
Co(1)–O(1)
O(3)#1–Co(1)–O(1)
O(3)#1–Co(1)–N(3)
1.955(14)
122.52(6)
99.60(6)
Co(1)–N(1)
O(3)#1–Co(1)–N(1)
O(1)–Co(1)–N(3)
2.029(15)
122.09(6)
107.99(6)
Complex 5
Zn(1)–O(1)
Zn(1)–N(3)
O(4)–Zn(1)–N(1)
1.9304(16)
2.0608(18)
105.65(8)
Zn(1)–O(4)
O(1)–Zn(1)–O(4)
O(1)–Zn(1)–N(3)
1.9551(17)
116.03(8)
105.45(8)
Zn(1)–N(1)
O(1)–Zn(1)–N(1)
O(4)–Zn(1)–N(3)
2.047(2)
117.30(8)
99.53(7)
Complex 6
Co(1)–O(4)
Co(1)–O(3)
O(4)–Co(1)–O(1)
O(2)–Co(1)–O(3)
O(2)–Co(1)–N(4)
1.996(2)
2.059(2)
86.62(11)
94.25(11)
109.31(10)
Co(1)–O(2)
Co(1)–N(4)
O(2)–Co(1)–O(1)
O(1)–Co(1)–O(3)
O(1)–Co(1)–N(4)
2.021(2)
2.173(3)
86.16(11)
161.40(9)
89.44(11)
Co(1)–O(1)
2.028(2)
O(4)–Co(1)–O(2)
O(4)–Co(1)–O(3)
O(4)–Co(1)–N(4)
O(3)–Co(1)–N(4)
159.85(1)
86.74(11)
89.40(11)
107.84(9)
Symmetry transformations used to generate equivalent atoms:
For 1: #1 ꢁx + 3/2, ꢁy + 1/2, z #2 ꢁx + 3/2, ꢁy ꢁ 1/2, z #3 ꢁx + 1, ꢁy + 1, ꢁz + 1.
For 2: #1 ꢁx, ꢁy, ꢁz + 2 #2 x, ꢁy ꢁ 1/2, z ꢁ 1/2 #3 x, ꢁy ꢁ 1/2, z + 1/2.
For 3: #1 x + 1/2, ꢁy + 1/2, z + 1/2 #2 ꢁx + 2, ꢁy, ꢁz + 2 #3 x ꢁ 1/2, ꢁy + 1/2, z ꢁ 1/2.
For 4: #1 x + 1/2, ꢁy + 1/2, z + 1/2 #2 x ꢁ 1/2, ꢁy + 1/2, z ꢁ 1/2 #3 ꢁx + 2, ꢁy, ꢁz.
For 5: #1 ꢁx + 1, ꢁy + 1, ꢁz + 1 #2 ꢁx, ꢁy + 2, ꢁz.
For 6: #1 ꢁx + 2, ꢁy, ꢁz + 1 #2 ꢁx + 1, ꢁy + 1, ꢁz.
2.2.7. [Co(pbmb)(1,2-bdc)]n (6)
corrugated network. Each Zn(II) atom is in a distorted tetrahedral
geometry coordinated by two oxygen atoms (O1, O1A) from two
1,4-bdc2ꢁ anions and two nitrogen atoms (N1, N1A) from two
pbmb (Fig. 1a). The Zn–O bond length is 2.022(2) Å and the Zn–N
bond length is 1.9575(17) Å, which are in the normal range [46].
The flexible pbmb adopts asymmetrical trans-conformation with
the Ndonorꢀ ꢀ ꢀN–Csp3ꢀ ꢀ ꢀCsp3 torsion angle of 78.649°. As exhibited
in Fig. 1b, each Zn(II) is bridged by two pbmb to form left-/right-
handed helices. Both the helical pitches are 11.031(2) Å corre-
sponding to the length of b-axis. Each 1,4-bdc2ꢁ is completely
deprotonated and bridges two Zn(II) through two carboxylates
with bis-monodentate mode, which supports left- and right-
handed helical chains arranged alternately to generate a 2D lay-
ered framework. The Znꢀ ꢀ ꢀZn distance across 1,4-bdc2ꢁ is
11.159 Å. The adjacent 2D layers are further interconnected to
The procedure is similar to that of 5, except that Co(NO3)2ꢀ6H2O
was used instead of Zn(NO3)2ꢀ6H2O. Yield: 70% (based on Co). Anal.
Calcd. for C27H20CoN4O4: C, 61.95; H, 3.85; N, 10.70. Found: C,
61.96; H, 3.87; N, 10.71%. IR (KBr, cmꢁ1): 1708 (w), 1617 (s),
1592 (m), 1569 (w), 1482 (w), 1375 (s), 1146 (w), 761 (m).
2.3. Single-crystal X-ray diffraction measurements
All data were collected on a Rigaku Saturn 724 detector with graph-
ite monochromatic Mo-Ka radiation (k = 0.71073 Å) at temperature of
20 1 °C. Absorption corrections were applied by using multi-scan
program. The data were collectedata temperature of 293(2) K and cor-
rected for Lorentz-polarization effects. All calculations were performed
using the SHELX-97 crystallographic software package [45]. 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 parameters and structural refinement for these
complexes are summarized in Table 1. Selected bond lengths and bond
angles of the six complexes are listed in Table 2.
product a 3D supramolecular framework by
pꢀ ꢀ ꢀp stacking interac-
tions [3.7474(8) Å] between the benzimidazole rings and the aro-
matic phenyl rings (Fig. 1c). Topological analysis (Fig. 1d) is
carried out to get insight of the structure of 1. If Zn(II) ion is sim-
plified as a 4-connected node, and pbmb and 1,4-bdc2ꢁ ligand
are defined as linkers, respectively, the 2D framework of 1 can be
described as a (4, 4) grid net.
3. Results and discussion
3.1.2. Crystal structure of complex 2
Single crystal X-ray diffraction analysis shows that 2 is also a 2D
layer structure. Each Co(II) ion is coordinated by four oxygen atoms
[Co-O (average) 1.953(65) Å] from four 1,4-bdc2ꢁ anions at the basal
positions and one axial nitrogen atom [Co–N = 2.0575(18) Å] from
pbmb to furnish a square pyramidal geometry (Fig. 2a). The Co–N
and Co–O bond lengths are similar to those of the known
3.1. Structure description
3.1.1. Crystal structure of complex 1
Single crystal X-ray diffraction analysis shows that complex 1
crystallizes in the orthorhombic space group Pccn and is a 2D

L. Liu et al. / Inorganica Chimica Acta 391 (2012) 66–74
69
Fig. 1. (a) Coordination environment of Zn(II) ion in 1 with hydrogen atoms omitted for clarity. (b) View of the 2D polymeric layer in ab plane with the charming left (M) and
right (P) handed helical chains arranging alternately. (c) View of the packing diagram of 1 (white, gray and black represent three adjacent 2D layer, severally) and the
illustration of p–p
interactions between 1,4-bdc2ꢁ and pbmb in neighboring layers. (d) The corrugated 2D layer structure with (4, 4) net.
Fig. 2. (a) Coordination environment of Co(II) ion in 2 with hydrogen atoms omitted for clarity. (b) 2D layered structure of complex 2 in the bc plane (left) and schematic
representation of a single (4, 4) net (right). (c) Schematic view of 3D structure with water molecules in 2. (d) The illustration of p–p interactions between two neighboring
layers (hydrogen atoms and the part of the structure are omitted for clarity).

70
L. Liu et al. / Inorganica Chimica Acta 391 (2012) 66–74
coordination complexes [47]. Two carboxylate groups of 1,4-bdc2ꢁ
both adopt bis-monodentate coordination mode. Each pair of Co(II)
ions is bridged by four 1,4-bdc2ꢁ anions to product a well-known
paddle-wheel binuclear clusters with a Coꢀ ꢀ ꢀCo separation of
2.942 Å. The binuclear clusters [Co2(CO2)4], serving as secondary
building units (SBUs), are further extended by 1,4-bdc2ꢁ anions into
a 2D coplanar (4, 4) grid net (Fig. 2b), different with that in 1. Inter-
estingly, the axial sites of the SBUs are occupied by two dangling
Fig. 3. (a) Molecular structure of 3 showing the local coordination geometry of Zn(II) ion with the atom labels (hydrogen atoms are omitted for clarity). (b) The 1D zigzag
chain constructed by 1,3-bdc2ꢁ and Zn(II) ions along the b-axis. (c) View of the 2D layer accomplished by joining all zigzag chains through [Zn2(pbmb)2] units. (d) Schematic
representation of 3-connected 63 topologies in 3. (e) View of the 3D supramolecular structure of 3 formed by
p–p stacking interactions between benzimidazoles rings of
adjacent pbmb (hydrogen atoms and the part of the structure are omitted for clarity).

L. Liu et al. / Inorganica Chimica Acta 391 (2012) 66–74
71
pbmb and the water molecules locate in the quare-grids (Fig. 2c). In
addition, the adjacent layers are held together by interactions
between the imidazole rings and the phenyl rings of benzimidazole
(the interplanar distance is 3.8713 Å) from opposite directions lead-
ing to a 3D supramolecular framework (Fig. 2d).
crystallographically independent Zn(II) center (Fig. 3a). The Zn(II)
center displays a distorted tetrahedral geometry, ligated by two
nitrogen atoms from two separate pbmb as well as two oxygen
atoms from two different 1,3-bdc2ꢁ anions. The Zn–O distances
are in the range of 1.9378(2)–1.944(2) Å, while Zn–N distances vary
from 2.027(2) to 2.068(2) Å. They are reasonable to compare with
those in reported works. As shown in Fig. 3b, both carboxylate
groups of rigid 1,3-bdc2ꢁ anions adopt the monodentate-bridging
coordination fashion to link two Zn(II) atoms giving rise to a 1D
zigzag chain with the Znꢀ ꢀ ꢀZn distance of 8.0105 Å. pbmb adopts
pꢀ ꢀ ꢀp
3.1.3. Crystal structures of complexes 3 and 4
X-ray single crystal diffraction reveals that complexes 3 and 4 are
isomorphous. Herein, only the structure of 3 is discussed in detail. 3
crystallizes in the monoclinic space group P21/n and has only one
Fig. 4. (a) Coordination environments of Zn(II) in complex 5 (hydrogen atoms are omitted for clarity). (b) View of the 1D double chains formed by the Zn2(pbmb)2(1,2-bdc)2
units along the b-axis. (c) View of weak interactions between the adjoining chains of 5.
Fig. 5. (a) Solid-state emission spectra of pbmb, 1,4-H2bdc and complex 1; (b) solid-state emission spectra of pbmb, 1,3-H2bdc and complex 3 and (c) solid-state emission
spectra of pbmb, 1,2-H2bdc and complex 5.

72
L. Liu et al. / Inorganica Chimica Acta 391 (2012) 66–74
asymmetric trans-conformation with two different Ndonorꢀ ꢀ ꢀN–
Csp3ꢀ ꢀ ꢀCsp3 torsion angles of 74.828° and 78.649°. Two pbmb share
two adjacent Zn(II) atoms arising from neighbouring chains to gen-
erate a [Zn2(pbmb)2] building unit. Interestingly, all the neighboring
1D chains can be connected by [Zn2(pbmb)2] units into a 2D frame-
work (Fig. 3c). The Znꢀ ꢀ ꢀZn distance across two pbmb is 10.4795 Å.
From a topological perspective, if Zn(II) ion is simplified as a 3-con-
nected node and the ligands are considered as linkers, the 2D struc-
ture can be described as a 63 topology (Fig. 3d). Furthermore, the
adjacent 2D layers are extended into a 3D supramolecular frame-
respectively. In 1, 1,4-bdc2ꢁ bridges Zn(II) ions to generate a 1D
zigzag chain, which is extended by pbmb resulting in a 2D (4, 4)
network with left- and right-handed helical chains arranged alter-
nately. While 2 owns a well-known paddle-wheel binuclear clus-
ters, which is expanded by 1,4-bdc2ꢁ anions to give rise to a 2D
(4, 4) grid net. For 3 and 4, M(II) (M = Zn or Co) are linked by
1,3-bdc2ꢁ anions to form a 1D zigzag chain, the introduce of pbmb
into the system lead to a 2D 63 topologies. In the structures of 5
and 6, two M(II) (M = Zn or Co) centers are bridged by 1,2-bdc2ꢁ
anions to product a dinuclear unit that is further connected by
pbmb to exhibit a 1D double-chain structure. These results demon-
strate that the coordination behavior of rigid carboxylate coligands
have significant contributions to the conformation of complexes
and provide the potential for directing the coordination of flexible
ligands with metal ions during the two-ligand assembly system.
work by the
pꢀ ꢀ ꢀp stacking interactions with the interplanar separa-
tion of 3.402 Å [center-to-center separation: 3.563 Å; the dihedral
angle: 0.5°] between neighboring imidazole rings and phenyl rings
from benzimidazoles (Fig. 3e) [48].
3.1.4. Crystal structure of complexes 5 and 6
Complexes 5 and 6 are isostructural. The structure of 5 is de-
scribed in detail as a typical example. As depicted in Fig. 4a, the
Zn(II) ion adopts a distorted tetrahedral geometry via coordinating
with two oxygen atoms (Zn1–O1 = 1.9304(16) Å, Zn1–O4 = 1.9551
(17) Å) from two 1,2-bdc2ꢁ anions as well as two nitrogen atoms
(Zn1–N1 = 2.047(2) Å, Zn1–N3 = 2.0608(18) Å) from two pbmb.
The bond angles around the Zn(II) ion are in the range of
99.53(7)–117.30(8)°. The two carboxylic groups of 1,2-bdc2ꢁ an-
ions adopt the monodentate-bridging coordination mode. pbmb
takes on asymmetric trans-conformation with two different
Ndonorꢀ ꢀ ꢀN–Csp3ꢀ ꢀ ꢀCsp3 torsion angles of 112.631° and 76.048°.
Every two pbmb and two 1,2-bdc2ꢁ are linked by adjacent Zn(II)
ions to form two types of units, [Zn2(1,2-bdc2ꢁ)2] and [Zn2(pb
mb)2]. The Znꢀ ꢀ ꢀZn distance across pbmb and 1,2-bdc2ꢁ is 9.2209
and 5.1746 Å, respectively. The two types of units are arranged
alternately via metal knots leading to the generation of a one-
dimensional (1D) double-chain structure (Fig. 4b). Moreover, adja-
cent two units are approximately oriented perpendicular to each
other, creating a twisted figure eight configuration [49]. It is note-
worthy that, the imidazole rings and phenyl rings of neighboring
benzimidazole between intermolecular chains are parallel each
other (Fig. 4c). The distance is 4.3619° or 4.3534A° indicating the
interactions are very weak [50].
3.3. Luminescence properties
The coordination complexes with d10 metal centers have been
studied for fluorescence properties [51,52] and potential applica-
tions as photoactive materials [53,54]. The solid-state photolumi-
nescence properties of 1, 3 and 5, together with the free bmb
ligand and all of the aromatic carboxylic acids were investigated
at ambient temperature, as depicted in Fig. 5. The photolumines-
cent spectra of 1,4-H2bdc, 1,3-H2bdc, and 1,2-H2bdc show different
emission peak of at 388, 369 and 343 nm, respectively. pbmb dis-
plays an intense emission band at 310 nm upon excitation at
283 nm, which may be attributed to p⁄
? p transitions [55]. The
emission band of complex 1 appears in 384 nm. Since it is similar
to that of 1,4-H2bdc, the emission can probably be assigned to the
intraligand charge transitions of 1,4-H2bdc. Notably, large red
shifted emission occurs in 3 (kem = 465 nm, kex = 400 nm) with re-
spect to the free ligands (1,4-H2bdc and pbmb), and such broad
band may be tentatively attributable to ligand-to-metal charge
transfer (LMCT) as reported for other ZnII complexes with N-donor
ligands [56]. As to 5, the emission of 464 nm (kex = 407 nm) with a
larger red-shifted (121 nm) as compared with the free ligands (1,2-
H2bdc and pbmb) may be tentatively assigned to LMCT [57,58].
From the above discussion, complexes 1, 3, and 5, which have
the same metal center and N-donor ligand as well as similar
coordination environments, show different photoluminescence
behaviors. The differences between the emission peaks for 1, 3
and 5 are probably ascribed to the differences in the aromatic car-
boxylate coligands [59]. The results indicate that the coligands
have an important influence on the photoluminescence behaviors.
3.2. Effects of positional isomer in dicarboxylate anions on the
structures of complexes 1–6
From the structures of complexes 1–6, it can be seen that pbmb
mainly coordinates with metal ions by its two exo-N-donors,
which adopts bidentate coordination mode. And two free-rotating
benzimidazole rings situated at para-positions of the alkyl spacer
act as anchors. The coordination behavior of dicarboxylate anions
also has essential influence on the structures of complexes. 1,4-
bdc2ꢁ, 1,3-bdc2ꢁ and 1,2-bdc2ꢁ possess different steric hindrance
and two carboxylate groups have 180°, 120° and 60° angles,
3.4. Thermogravimetric analysis (TGA)
The thermal stability of the six complexes was also estimated
(Fig. 6). The TGA curve of complex 1 exhibits that it is stable up
to 274 °C and then loses weight from 274 to 593 °C, corresponding
Fig. 6. Thermogravimetric curve of complexes 1–6.

L. Liu et al. / Inorganica Chimica Acta 391 (2012) 66–74
73
to the decomposition of pbmb and 1,4-bdc2ꢁ. The remaining
weight corresponds to the formation of ZnO (obsd, 13.30%; calcd,
15.25%). Complex 2 shows a weight loss of 4.97% from 42 to
143 °C corresponding to the release of lattice water molecule
(calcd, 4.80%), and then, a plateau region is observed. The overall
framework of 2 begins to decompose from 278 °C, and the CoO res-
idue of 11.55% (calcd, 13.39%) is observed at 493 °C. For anhydrous
complex 3, the removal of the framework occurs in the range of
240–602 °C. The remaining weight corresponds to the formation
of ZnO (obsd, 13.53%; calcd, 15.25%). Polymer 4 displays a high
thermal stability, which is stable up to 388 °C and then keeps los-
ing weight until to 588 °C corresponding to the losses of pbmb and
the decomposition of 1,3-bdc2ꢁ. Finally, the white CoO residue of
15.34% (calcd, 14.21%) is observed. The framework of 5 remains in-
tact until it is heated to 314 °C, and the ZnO residue of 16.54%
(calcd, 15.25%) is obtained at 583 °C. The TGA curve of 6 shows a
one step weight loss process from 306 to 519 °C, corresponding
to the decomposition of organic components. A CoO residue of
14.89% (calcd, 14.21%) is observed.
[4] (a) H.D. Guo, D.F. Qiu, X.M. Guo, G.L. Zheng, X. Wang, H.J. Zhang, Cryst. Eng.
Comm. 11 (2009) 2425;
(b) F. Luo, Y.X. Che, J.M. Zheng, Cryst. Growth Des. 9 (2009) 1066;
(c) H.Y. Yang, L.K. Li, J. Wu, H.W. Hou, B. Xiao, Y.T. Fang, Eur. Chem. 15 (2009)
4049.
[5] C. Janiak, Dalton Trans. (2003) 2781.
[6] U. Mueller, M. Schubert, F. Teich, H. Puetter, K.S. Arndt, J. Pastré, J. Mater. Chem.
16 (2006) 626.
[7] C. Janiak, J.K. Vieth, New J. Chem. 34 (2010) 2366.
[8] P. Kanoo, K.L. Gurunatha, T.K. Maji, Cryst. Growth Des. 9 (2009) 4147.
[9] (a) W.H. Wang, P.H. Xi, X.Y. Su, J.B. Lan, Z.H. Mao, J.S. You, R.G. Xie, Cryst.
Growth Des. 7 (2007) 741;
(b) P.J. Hagrman, D. Hagrman, J. Zubieta, Angew. Chem., Int. Ed. 38 (1999)
2638.
[10] M. Du, Z.H. Zhang, X.G. Wang, L.F. Tang, X.J. Zhao, CrystEngComm 10 (2008)
1855.
[11] C.D. Jia, J.J. Liang, J. Yang, X.J. Huang, X.J. Yang, B. Wua, N. Tang, Z. Anorg, Allg.
Chem. 634 (2008) 1210.
[12] C.B. Aakeröy, N.R. Champness, C. Janiak, Cryst. Eng. Comm. 12 (2010) 22.
[13] B.F. Hoskins, R. Robson, D.A. Slizys, J. Am. Chem. Soc. 119 (1997) 2952.
[14] L. Song, J.R. Li, P. Lin, Z.H. Li, T. Li, S.W. Du, X.T. Wu, Inorg. Chem. 45 (2006)
10155.
[15] (a) L. Carlucci, G. Ciani, D.M. Proserpio, Chem. Commun. (2004) 380;
(b) Y.T. Wang, M.L. Tong, H.H. Fan, H.Z. Wang, X.M. Chen, Dalton Trans. (2005)
424.
[16] J. Tao, M.L. Tong, J.X. Shi, X.M. Chen, S.W. Ng, Chem. Commun. (2000) 2043.
[17] X. Li, B.L. Wu, C.Y. Niu, Y.Y. Niu, H.Y. Zhang, Cryst. Growth Des. 9 (2009) 3423.
[18] (a) M.X. Li, P. Cai, C.Y. Duan, F. Lu, J. Xie, Q.J. Meng, Inorg. Chem. 43 (2004)
5174;
4. Conclusion
(b) A.V. Davis, K.N. Raymond, J. Am. Chem. Soc. 127 (2005) 7912.
[19] (a) L. Carlucci, G. Ciani, D.M. Proserpi, Chem. Commun. (2004) 380;
(b) X.L. Zhang, C.P. Guo, Q.Y. Yang, W. Wang, W.S. Liu, B.S. Kang, C.Y. Su, Chem.
Commun. (2007) 4242.
[20] (a) M.B. Klaus, M. Yassin, Chem. Commun. (2006) 2060;
(b) C. Qin, X.L. Wang, E.B. Wang, Z.M. Su, Inorg. Chem. 49 (2010) 11643;
(c) B.L. Li, Y.F. Peng, B.Z. Li, Y. Zhang, Chem. Commun. (2005) 2333.
[21] J. Yang, J.F. Ma, Y.Y. Liu, S.R. Batten, Cryst. Eng. Comm. 11 (2009) 151.
[22] (a) B.F. Hoskins, R. Robson, D.A. Slizys, J. Am. Chem. Soc. 119 (1997) 2952;
(b) B.F. Hoskins, R. Robson, D.A. Slizys, Angew. Chem., Int. Ed. Engl. 36 (1997)
2336;
In summary, a series of Zn(II)/Co(II)-containing coordination
complexes based on a flexible bis(methylbenzimidazole) ligand
and isomeric benzenedicarboxylates have been successfully con-
structed and synthesized under hydrothermal conditions. These
complexes show different 1D and 2D frameworks. The results
demonstrate that the use of flexible ligand is a good strategy for
facilitating the formation of diversified structures. In addition,
the isomeric benzenedicarboxylates play crucial roles in the con-
struction of coordination complexes. This work will undoubtedly
deepen our systemic understanding for the effect of positional iso-
mer in aromatic dicarboxylic acids on the final structures. More-
over, 1, 3 and 5 show fluorescence properties, and maybe display
potential for optical materials. 1–6 present high thermal stabilities.
The further studies will be focused on properties of a series of coor-
dination complexes constructed by the bis(methylbenzimida-
zole)ligands and other aromatic polycarboxylate ligands.
(c) L. Carlucci, G. Ciani, D.M. Proserpio, Chem. Commun. (2004) 380;
(d) L. Carlucci, G. Ciani, D.M. Proserpio, L. Spadacini, Cryst. Eng. Comm. 6
(2004) 96.
[23] (a) S.K. Chawla, M. Arora, K. Nättinen, K. Rissanen, J.V. Yakhmi, Polyhedron 23
(2004) 3007;
(b) L. Carlucci, G. Ciani, D.M. Proserpio, Cryst. Growth Des. 5 (2005) 37;
(c) L. Zhang, X.Q. Lü, C.L. Chen, H.Y. Tan, H.X. Zhang, B.S. Kang, Cryst. Growth
Des. 5 (2005) 283;
(d) H.F. Zhu, J. Fan, T. Okamura, W.Y. Sun, N. Ueyama, Cryst. Growth Des. 5
(2005) 289.
[24] H.A. Habib, A. Hoffmann, H.A. Höppea, C. Janiak, Dalton Trans. (2009) 1742.
[25] H.A. Habib, A. Hoffmann, H.A. Höppe, G. Steinfeld, C. Janiak, Inorg. Chem. 48
(2009) 2166.
[26] X.R. Meng, Y.L. Song, H.W. Hou, Y.T. Fan, G. Li, Y. Zhu, Inorg. Chem. 42 (2003)
1306.
[27] (a) Z.G. Gu, Y.F. Xu, X.H. Zhou, J.L. Zuo, X.Z. You, Cryst. Growth Des. 8 (2008)
1306;
(b) C. Janiak, T.G. Scharmann, P. Albrecht, F. Marlow, R. Macdonald, J. Am.
Chem. Soc. 118 (1996) 6307.
[28] (a) X.R. Meng, Y.L. Song, H.W. Hou, H.Y. Han, B. Xiao, Y.T. Fan, Y. Zhu, Inorg.
Chem. 43 (2004) 3528;
Acknowledgements
We gratefully acknowledge the financial support by the Na-
tional Natural Science Foundation of China (Nos. 20971110 and
91022013), and the Outstanding Talents Foundation by the Henan
Province.
(b) B.L. Li, Y.F. Peng, B.Z. Li, Y. Zhang, Chem. Commun. (2005) 2333;
(c) B.F. Hoskins, R. Robson, D.A. Slizys, J. Am. Chem. Soc. 119 (1997) 2952.
[29] (a) Y.B. Dong, X. Zhao, R.Q. Huang, M.D. Smith, H. ZurLoye, Inorg. Chem. 43
(2004) 5603;
(b) F.N. Dai, J.M. Dou, H.Y. He, X.L. Zhao, D.F. Sun, Inorg. Chem. 49 (2010) 4117.
[30] C.Y. Xu, Q.Q. Guo, X.J. Wang, H.W. Hou, Y.T. Fan, Cryst. Growth Des. 11 (2011)
1869.
[31] C.Y. Xu, L.K. Li, Y.P. Wang, Q.Q. Guo, X.J. Wang, H.W. Hou, Y.T. Fan, Cryst.
Growth Des. 11 (2011) 4667.
[32] Y.J. Mu, J.H. Fu, Y.J. Song, Z. Li, H.W. Hou, Y.T. Fan, Cryst. Growth Des. 11 (2011)
2183.
Appendix A. Supplementary material
CCDC 862548, 862549, 862550, 862551, 862552 and 862553
contain the supplementary crystallographic data for complexes 1,
2, 3, 4, 5 and 6, respectively. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2012.04.043.
[33] Y.J. Mu, Y.J. Song, C. Wang, H.W. Hou, Y.T. Fan, Inorg. Chim. Acta 365 (2011)
167.
[34] H.A. Habib, J. Sanchiz, C. Janiak, Inorg. Chim. Acta 362 (2009) 2452.
[35] (a) C. Ren, P. Liu, Y.Y. Wang, W.H. Huang, Q.Z. Shi, Eur. J. Inorg. Chem. 35 (2010)
5545;
References
(b) J.Y. Hu, J.P. Li, J.A. Zhao, H.W. Hou, Y.T. Fan, Inorg. Chim. Acta 362 (2009)
5023;
[1] (a) J.L. Du, T.L. Hu, S.M. Zhang, Y.F. Zeng, X.H. Bu, Cryst. Eng. Comm. 10 (2008)
1866;
(c) A.X. Tian, J. Ying, J. Peng, J.Q. Sha, Z.G. Han, J.F. Ma, Z.M. Su, N.H. Hu, H.Q. Jia,
Inorg. Chem. 47 (2008) 3274.
(b) L.X. Sun, Y. Qi, Y.M. Wang, Y.X. Che, J.M. Zheng, Cryst. Eng. Comm. 12 (2010)
1540.
[36] C.J. Zhang, H.J. Pang, Q. Tang, H.Y. Wang, Y.G. Chen, J. Solid State Chem. 183
(2010) 2945.
[37] J.C. Dai, X.T. Wu, S.M. Hu, Z.Y. Fu, J.J. Zhang, W.X. Du, H.H. Zhang, R.Q. Sun, Eur.
J. Inorg. Chem. 10 (2004) 2096.
[2] T. Li, N. Yang, G.Y. Zhao, Inorg. Chem. Com. 13 (2010) 1497.
[3] (a) K.M. Blake, L.L. Johnston, J.H. Nettleman, R.M. Supkowskib, R.L.L. Duca,
Cryst. Eng. Comm. 12 (2010) 1927;
(b) S.R. Batten, Cryst. Eng. Comm. 18 (2001) 1.

74
L. Liu et al. / Inorganica Chimica Acta 391 (2012) 66–74
[38] (a) E. Fournier, F. Lebrun, M. Drouin, A. Decken, P.D. Harvey, Inorg. Chem. 43
(2004) 3127;
[51] P. Ren, M.L. Liu, J. Zhang, W. Shi, P. Cheng, D.Z. Liao, S.P. Yan, Dalton Trans.
(2008) 4711.
(b) Y.Q. Zheng, J.L. Lin, Z.P. Kong, Inorg. Chem. 43 (2004) 2590;
(c) E.Q. Gao, S.Q. Bai, Z.M. Wang, C.H. Yan, Dalton Trans. (2003) 1759.
[39] H.A. Habib, J. Sanchiz, C. Janiak, Inorg. Chim. Acta 362 (2009) 2452.
[40] B. Wisser, Y.R. Lu, C. Janiak, Z. Anorg, Allg. Chem. 633 (2007) 1189.
[41] H.A. Habib, J. Sanchiz, C. Janiak, Dalton Trans. (2008) 1734.
[42] S.K. Henninger, H.A. Habib, C. Janiak, J. Am. Chem. Soc. 131 (2009) 2776.
[43] H.Y. Bai, J.F. Ma, J. Yang, L.P. Zhang, J.C. Ma, Y.Y. Liu, Cryst. Growth Des. 10
(2010) 1946.
[52] S.Q. Zang, Y. Su, Y.Z. Li, J.Q. Lin, X.Y. Duan, Q.J. Meng, S. Gao, Cryst. Eng. Comm.
11 (2009) 122.
[53] P. Mahata, S. Natarajan, Eur. J. Inorg. Chem. 2005 (2005) 2156.
[54] (a) J.C. Dai, X.T. Wu, Z.Y. Fu, C.P. Cui, S.H. Hu, W.X. Du, L.M. Wu, H.H. Zhang, R.Q.
Sun, Inorg. Chem. 41 (2002) 1391;
(b) J. Tao, X. Yin, Z.B. Wei, R.B. Huang, L.S. Zheng, Eur. J. Inorg. Chem. 2004
(2004) 125;
(c) T. Jiang, X.M. Zhang, Cryst. Growth Des. 8 (2008) 3077;
(d) S.R. Li, L. Xu, Inorg. Chem. 44 (2005) 3731.
[44] R. Bronisz, Inorg. Chem. 44 (2005) 4463.
[45] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[46] B. Xiao, H.Y. Han, X.R. Meng, Y.L. Song, Y.T. Fan, H.W. Hou, Y. Zhu, Inorg. Chem.
Commun. 7 (2004) 378.
[47] Y. Qi, F. Luo, S.R. Batten, Y.X. Che, J.M. Zheng, Cryst. Growth Des. 8 (2008) 2806.
[48] C. Janiak, J. Chem. Soc., Dalton Trans. (2000) 3885.
[49] V. Chandrasekhar, P. Singh, Cryst. Growth Des. 10 (2010) 3077.
[50] (a) J.Q. Chen, Y.P. Cai, H.C. Fang, Z.Y. Zhou, X.L. Zhan, G. Zhao, Z. Zhang, Cryst.
Growth Des. 9 (2009) 5244;
[55] W.L. Liu, L.H. Ye, X.F. Liu, L.M. Yuan, J.X. Jiang, C.G. Yan, Cryst. Eng. Comm. 10
(2008) 1395.
[56] H.Y. Liu, H. Wu, J.F. Ma, Y.Y. Liu, B. Liu, J. Yang, Cryst. Growth Des. 11 (2010) 4795.
[57] S.L. Zheng, J.H. Yang, X.L. Yu, X.M. Chen, W.T. Wong, Inorg. Chem. 43 (2004)
830.
[58] S.L. Zheng, X.M. Chen, Aust. J. Chem. 57 (2004) 703.
[59] (a) Y.Y. Liu, Z.H. Wang, J. Yang, B. Liu, Y.Y. Liu, J.F. Ma, CrystEngComm 13 (2011)
3811;
(b) L. Liu, Z.F. Li, B.L. Wang, G. Li, L.P. Wang, X.R. Meng, Z.H. He, Cryst. Growth
Des. 9 (2009) 1605.
(b) J.S. Hu, Y.J. Shang, X.Q. Yao, L. Qin, Y.Z. Li, Z.J. Guo, H.G. Zheng, Z.L. Xue,
Cryst. Growth Des. 10 (2010) 2676.