Structural and luminescent properties of a series of Cd(II) pyridyl benzimidazole complexes that exhibit extended three-dimensional hydrogen bonded networks

Article abstract of DOI:10.1080/00958972.2017.1299143

Five new coordination complexes, [CdI₂(3-PyBim)](H₂O)₃ (1), [Cd(SO₄)(3-PyBim)(H₂O)₄] (2), [CdCl₂(4-PyBim)₂(H₂O)₂] (3), [CdBr₂(4-PyBim)₂(H₂O)₂] (4) and [CdI₂(4-PyBim)₂(H₂O)₂] (5) [3-PyBim=2-Pyridin-3-yl-1H-benzoimidazole, 4-PyBim=2-Pyridin-4-yl-1H-benzoimidazole], were obtained under hydrothermal conditions and characterized by single crystal X-ray diffraction, IR, elemental analysis, and powder X-ray diffraction. All of the complexes have mononuclear structures. Among the crystal structures of these complexes, there exist a variety of intermolecular hydrogen bonding interactions and π?π interactions, which further extend to a 3-D supramolecular architecture. The solid state photoluminescent properties of 1–5 vary with the electronegativity of the coordination anion. Additionally, the thermogravimetric analyses of these complexes are discussed.

Full text of DOI:10.1080/00958972.2017.1299143

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Structural and luminescent properties of a series
of Cd(II) pyridyl benzimidazole complexes that
exhibit extended three-dimensional hydrogen
bonded networks
Jin-Hua Wang, Gui-Mei Tang, Ting-Xiao Qin, Yong-Tao Wang, Yue-Zhi Cui &
Seik Weng Ng
To cite this article: Jin-Hua Wang, Gui-Mei Tang, Ting-Xiao Qin, Yong-Tao Wang, Yue-Zhi
Cui & Seik Weng Ng (2017): Structural and luminescent properties of a series of Cd(II) pyridyl
benzimidazole complexes that exhibit extended three-dimensional hydrogen bonded networks,
Journal of Coordination Chemistry, DOI: 10.1080/00958972.2017.1299143
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Date: 13 March 2017, At: 16:09

Journal of Coordination Chemistry, 2017
http://dx.doi.org/10.1080/00958972.2017.1299143
Structural and luminescent properties of a series of Cd(II)
pyridyl benzimidazole complexes that exhibit extended
three-dimensional hydrogen bonded networks
Jin-Hua Wanga, Gui-Mei Tanga, Ting-Xiao Qina, Yong-Tao Wanga, Yue-Zhi Cuia and
Seik Weng Ngb
adepartment of Chemical engineering, shandong Provincial Key laboratory of fine Chemicals, Qilu
university of technology, Jinan, P.r. China; bfaculty of science, Chemistry department, King abdulaziz
university, Jeddah, saudi arabia
ABSTRACT
ARTICLE HISTORY
received 25 october 2015
accepted 13 february 2017
Five new coordination complexes, [CdI2(3-PyBim)](H2O)3 (1), [Cd(SO4)
(3-PyBim)(H2O)4] (2), [CdCl2(4-PyBim)2(H2O)2] (3), [CdBr2(4-PyBim)2
(H2O)2] (4) and [CdI2(4-PyBim)2(H2O)2] (5) [3-PyBim=2-Pyridin-3-yl-1H-
benzoimidazole, 4-PyBim=2-Pyridin-4-yl-1H-benzoimidazole], were
obtained under hydrothermal conditions and characterized by
single crystal X-ray diffraction, IR, elemental analysis, and powder
X-ray diffraction. All of the complexes have mononuclear structures.
Among the crystal structures of these complexes, there exist a variety
of intermolecular hydrogen bonding interactions and π⋯π interactions,
which further extend to a 3-D supramolecular architecture. The solid
statephotoluminescentpropertiesof1–5varywiththeelectronegativity
of the coordination anion. Additionally, the thermogravimetric analyses
of these complexes are discussed.
KEYWORDS
metal coordination
complexes; N-heterocyclic
ligand; self-assembly;
tunable luminescence;
cadmium; anions
100
3-PyBim
4-PyBim
1
2
3
80
60
4
5
40
20
0
400
500
600
700
Wavelength (nm)
CONTACT Gui-mei tang
meiguit@qlu.edu.cn; yong-tao Wang
ceswyt@qlu.edu.cn
supplemental data for this article can be accessed at http://dx.doi.org/10.1080/00958972.2017.1299143.
© 2017 informa uK limited, trading as taylor & francis Group

2
J.-H. WANG ET AL.
1. Introduction
Research has been directed toward coordination complexes that exhibit extended solid
state structures [1]. Much of this work has been driven by the ability of such structures to
exhibit luminescence [2], drug delivery [3], ferroelectricity [4], non-linear optics [5], gas stor-
age and separation [6], catalysis [7] and magnetism [8]. Several factors need to be taken into
account in constructing materials with extended solid state structures, the metal ions [9],
the ligands [10], the counter anions [11], the reaction temperature [12], the pH of the reaction
[13] and the solvents [14]. The ligands and counter anions play a pivotal role for self-assembly
and the structures of final products. To synthesize coordination complexes with the desired
extended three-dimensional structures, the choices of ligand, metal ion, and counter ion
are critical [15]. Recently, coordination complexes that exhibit extended solid state structures
and frameworks have been prepared using N-heterocyclic ligands [16]. For example, a series
of d10 coordination complexes with pyrazolyl ligands have been reported by Ding et al., and
the solid-state luminescent properties revealed that the emission maximum can be tuned
from 372 to 486 nm [17]. Although some progress has been made on using coordination
complexes as building blocks for extended three-dimensional frameworks, predicted syn-
thesis of such frameworks remains a great challenge.
Coordination complexes of d10 metal ions have interesting luminescence. Their lumines-
cent behavior can be tuned by variation of the organic ligands and the coordinated counter
anions [18]. A few metal complexes with excellent fluorescence have been reported [19],
and we are interested in incorporating highly luminescent coordination complexes into
three-dimensional solid state networks.
We would like to design complexes with interesting luminescence for investigating the
relationship between the structures and properties. Therefore, we synthesized two ligands
containing N-heterocyclic groups, 2-pyridin-3-yl-1H-benzoimidazole (3-PyBim), and 2-pyri-
din-4-yl-1H-benzoimidazole (4-PyBim) (Scheme 1). Both heterocyclic ligands possess the
following features: (i) the nitrogen from pyridine can take part in coordinating with metal
ions; (ii) two nitrogens from imidazole can act as acceptor and donor of hydrogen bonds,
consolidating the thermal stabilities of complexes; (iii) three types of aromatic rings such as
pyridine, phenyl, and imidazole can generate π⋯π packing interactions between aromatic
rings. Although some coordination complexes with 3-PyBim [20] and 4-PyBim [21] have
been reported, further development of coordination complexes remains a challenge.
Herein, we report syntheses, solid state structures, and luminescent properties for new
supramolecular coordination complexes, [CdI2(3-PyBim)4](H2O)3 (1), [Cd(SO4)(3-PyBim)
(H2O)4](2), [CdCl2(4-PyBim)2(H2O)2](3), [CdBr2(4-PyBim)2(H2O)2](4), and[CdI2(4-PyBim)2(H2O)2]
(5), which have been obtained under hydrothermal conditions. Luminescent properties of
these complexes can be tuned by the electronegativity of the coordinated anions.
H
N
3-PyBim
4-PyBim
N
N
H
N
N
N
Scheme 1. the structures of 3-PyBim and 4-PyBim.

JOURNAL OF COORDINATION CHEMISTRY
3
2. Experimental
2.1. Materials and measurements
Reagents and solvents were commercially available and not purified. C, H, and N microana-
lyses were carried out with a Perkin-Elmer 240 elemental analyzer. The powder X-ray diffrac-
tion (PXRD) data were collected on a Bruker D8 diffractometer using Cu-Kα radiation.
Fluorescence measurements were recorded with an Edinburgh FLS920 fluorescence spec-
trophotometer. Thermogravimetric analyses (TGA) were carried out on aTA SDT Q600 thermal
analyzer under N2 with a heating rate of 10 °C min−1 from room temperature to 700 °C. All
microwave reactions were carried out on a Galanz G8023CSL-K3 microwave operating at
100 W.
2.2. Synthesis of 2-Pyridin-4-yl-1H-benzoimidazole (4-PyBim)
To a mixture solid of isonicotinic acid (1.477 g, 0.012 mol) and 12-phenylene diamine
(1.081 mg, 0.010 mol), which were ground and mixed adequately, polyphosphoric acid
(10 ml) was added. The reaction mixture was intermittently heated under microwave irra-
diation with 100-watt power. Subsequently, two blocks of ice were added. The reaction
mixture was allowed to cool to room temperature and then poured over water (30 ml).
The pH of the reaction mixture was adjusted to 7 by adding 10% NaOH solution. The solid
formed was filtered under reduced pressure and dried. Yield (85.9%, 1.675 g). m.p. 224–
230 °C. The microanalysis of 4-PyBim was in accord with those of the compound reported
previously [22].
2.3. Synthesis of 2-Pyridin-3-yl-1H-benzoimidazole (3-PyBim)
The preparation of 1 was similar to that of 4-PyBim except that nicotinic acid was used
instead of isonicotinic acid. The solid formed was collected and crystallized from pure water
to give a needle-like crystal. Yield (76.7%, 1.496 g). m.p. 263–269 °C. The microanalysis of 1
was in agreement with those of the compound reported previously [23].
2.4. Synthesis of [CdI2(3-PyBim)4](H2O)3 (1)
A reaction mixture of CdI2 (73.2 mg, 0.2 mmol), 3-PyBim (19.5 mg, 0.1 mmol), and water
(10 ml) was added to a 15 ml Teflon reactor under autogenous pressure at 160 °C for 3 days
and then cooled to room temperature at 5 °C h−1. Pale yellow crystals of 1 suitable for dif-
fraction analysis were obtained. (31 mg, Yield: 25.2%). Analysis found (%): C, 48.89; H, 3.50;
N, 13.95; requires (%): C, 48.00; H, 3.52; N, 13.99; IR (KBr, cm−1): 3493 (m), 3169 (w), 3051 (w),
3010 (w), 2993 (w), 2929 (w), 2887 (w), 2794 (w), 2717 (w), 2603 (w), 2189 (w), 1581 (m), 1483
(m), 1433 (s), 1317 (m), 1280 (m), 1226 (m), 1192 (m), 1120 (m), 1047 (m), 966 (m), 923 (w),
817 (m), 744 (s), 700 (m), 638 (m), 408 (w).
2.5. Synthesis of [Cd(SO4)(3-PyBim)(H2O)4] (2)
The preparation of 2 was similar to that of 1 except that Cd(SO4)∙8/3H2O (77.0 mg, 0.1 mmol)
was used instead of CdI2 (36.6 mg, 0.1 mmol). Faint pink crystals of 2 were collected. (31 mg,

4
J.-H. WANG ET AL.
Yield: 65.2%). Analysis found (%): C, 30.55; H, 3.61; N, 8.80; requires (%): C, 30.29; H, 3.60; N,
8.83; IR (KBr, cm−1): 3206 (br), 3091 (br), 2976 (br), 1589 (w), 1556 (m), 1531 (s),1489 (s), 1454
(m), 1393 (s), 1317 (w), 1279 (w), 1247 (w), 1229 (w), 1194 (w), 1113 (m), 1107 (m), 1049 (w),
1005 (w), 968 (m), 932 (w), 910 (w), 879 (w), 822 (w), 764 (w), 743 (s), 694 (s), 652 (w), 615 (w),
428 (m), 407 (w).
2.6. Synthesis of [CdCl2(4-PyBim)2(H2O)2] (3)
A reaction mixture of CdCl2∙5/2H2O (45.6 mg, 0.2 mmol), 4-PyBim (19.5 mg, 0.1 mmol), and
water (10 ml) was added to a 15 ml Teflon reactor under autogenous pressure at 160 °C for
3 days and then cooled to room temperature at 5 °C h−1. Pale yellow crystals of 3 were col-
lected. (23 mg, Yield: 18.9%). Analysis found (%): C, 47.57; H, 3.61; N, 13.73; requires (%): C,
47.27; H, 3.64; N, 13.78; IR (KBr, cm−1): 3510 (m), 3169 (s), 3149 (w), 3118 (w), 3059 (w), 2193
(w), 1938 (w), 1610 (s), 1448 (w), 1381 (w), 1315 (m), 1280 (w), 1230 (w), 1219 (w), 1149 (w),
1107 (w), 1070 (w), 1010 (w), 964 (w), 831 (m), 817 (w), 746 (s), 700 (w), 671 (m), 596 (w), 563
(m), 532 (w), 509 (w), 476 (w), 439 (w).
2.7. Synthesis of [CdBr2(4-PyBim)2(H2O)2] (4)
The preparation of 4 was similar to that of 3 except that CdBr2∙4H2O (34.4 mg, 0.1 mmol) was
used instead of CdCl2∙5/2H2O (22.8 mg, 0.1 mmol). Pale yellow crystals of 4 were collected.
(31 mg, Yield: 44.3%). Analysis found (%): C, 41.38; H, 3.15; N, 12.05; requires (%): C, 41.26; H,
3.17; N, 12.03; IR (KBr, cm−1): 3520 (m), 3223 (s), 3153 (w), 3116 (w), 3084 (w), 3057 (w), 2993
(w), 2900 (w), 2659 (w), 2084 (w), 2304 (w), 2158 (w), 1639 (m), 1610 (s), 1431 (s), 1313 (m),
1282 (m), 1220 (m), 1147 (m), 1109 (m), 1074 (w), 1012 (m), 972 (m), 823 (m), 752 (s), 698 (m),
644 (m), 561 (m), 511 (m), 437 (m), 414 (m).
2.8. Synthesis of [CdI2(4-PyBim)2(H2O)2] (5)
The preparation of 5 was similar to that of 3 except that CdI2 (36.6 mg, 0.1 mmol) was
used instead of CdCl2∙5/2H2O (22.8 mg, 0.1 mmol). Pale yellow crystals of 6 were collected.
(18 mg, Yield: 22.7%). Analysis found (%): C, 36.59; H, 2.82; N, 10.69; requires (%): C, 36.36;
H, 2.80; N, 10.60; IR (KBr, cm−1): 3523 (m), 3253 (s), 3151 (w), 3076 (w), 3049 (w), 2897 (w),
2655 (w), 2476 (w), 2324 (w), 2154 (w), 2005 (w), 1629 (m), 1608 (s), 1429 (s), 1311 (m),
1215 (m), 1145 (m), 1008 (m), 970 (m), 823 (m), 750 (s), 696 (m), 613 (m), 559 (m), 511 (m),
408 (m).
2.9. Single-crystal structure determination
Single-crystal structure determinations of single crystals of 1–5 were carried out with a
Bruker APEX II CCD diffractometer equipped with a graphite crystal monochromator.
X-ray intensity data of 1, 3, and 5 were measured at 293 K on a Bruker SMART APEX
CCD-based diffractometer with graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å),
respectively. Data for 4 were collected at 296 K and 2 was done at 100 K. All the measured
independent reflections were used in the structural analysis, and semi-empirical

JOURNAL OF COORDINATION CHEMISTRY
5
absorption corrections were applied using SADABS [24]. SAINT was used for integration
of the diffraction profiles [25]. The structure was solved by direct methods using the
SHELXS program of the SHELXTL package and refined with SHELXL [26]. All non-hydrogen
atoms were located in successive difference Fourier syntheses. The final refinement was
performed by full-matrix least-squares with anisotropic thermal parameters for all the
non-hydrogen atoms based on F2. The hydrogens were placed in calculated sites and
included in the final refinement in the riding model approximation with displacement
parameters derived from the parent to which they were bonded. Special computations
for the crystal structure discussions were carried out with PLATON for Windows [27].
Crystallographic data and other pertinent information for 1–5 are summarized in Table 1.
Selected bond lengths and angles are listed in Table 2. Corresponding hydrogen bonding
data are listed in Table 3. The data of weak π⋯π packing interactions are listed in Table 4.
Crystallographic data for the structural analysis have been deposited with the Cambridge
Crystallographic Data Center; CCDC references numbers are 994345–994350 for 1–5,
respectively. Copies of this information may be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44 1223 336 033; E-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk). Supplementary data associated
with this article can be found in the online version.
Table 1. Crystal data and structure refinement parameters for 1–5.
Compound refer-
ence
1
2
3
4
5
Chemical formula
formula mass
Crystal system
a/Å
C
48h42Cdi2n12o3
C12h17Cdn3o8s
475.75
monoclinic
7.8824(5)
10.2142(6)
19.9949(10)
90.00
99.768(5)
90.00
1586.50(16)
100(2)
C24h22CdCl2n6o2
609.78
C24h22Br2Cdn6o2
698.70
monoclinic
7.06300(10)
11.9111(2)
14.2997(2)
90.00
96.7570(10)
90.00
1194.65(3)
296(2)
C24h22Cdi2n6o2
792.68
1201.14
triclinic
triclinic
7.050(5)
9.236(5)
9.462(5)
76.619(5)
73.972(5)
87.396(5)
576.0(6)
293(2)
monoclinic
7.308(5)
12.250(5)
14.123(5)
90.000(5)
93.427(5)
90.000(5)
1262.1(11)
293(2)
12.2776(4)
12.4178(4)
16.5983(6)
102.386(2)
107.364(2)
90.110(2)
2353.14(14)
293(2)
b/Å
c/Å
α/°
β/°
γ/°
unit cell volume/Å3
temperature/K
space group
radiation type
absorption
coefficient, μ mm−1
no. of reflections
measured
no. of independent
reflections
Rint
P−1
P21/c
P−1
P21/c
P21/c
moKα
moKα
moKα
moKα
moKα
1.832
1.558
1.217
4.295
3.346
32,165
11,542
15,730
3679
4855
2770
10,551
2976
11,085
3125
0.0570
0.0588
0.0703
0.0529
0.0266
0.0255
0.0266
0.0222
0.0264
0.0217
final R1 values (I >
2σ(I))a
final wR(F2) values (I> 0.1458
2σ(I))
0.1389
0.0595
0.1418
0.0662
0.0262
0.0669
0.0548
0.0267
0.0561
0.0526
0.0238
0.0536
final R1 values (all
data)
0.1085
final wR(F2) values (all 0.1740
data)b
Goodness of fit on F2
CCdC number
1.025
994,346
1.197
994,347
1.037
994,348
1.056
994,349
1.107
994,350
aR1 = ∑||Fo| − |Fc||/∑|Fo|.
bwR2 = [∑[w(Fo2 − Fo2)2]/∑[w(Fo2)2]]1/2
.

6
J.-H. WANG ET AL.
Table 2. selected bond lengths (Å) and angles (°) for 1–5.
1
Cd1–i1
2.9134(6)
2.422(5)
Cd1–i2
Cd1–n4
2.9076(6)
2.448(5)
Cd1–n1
Cd1–n7
2.455(5)
Cd1–n10
2.434(6)
i1–Cd1–i2
i1–Cd1–n4
i1–Cd1–n10
i2–Cd1–n4
i2–Cd1–n10
n1–Cd1–n7
n4–Cd1–n7
n7–Cd1–n10
2
173.81(2)
88.04(12)
90.95(12)
87.24(12)
93.36(12)
92.95(16)
87.63(16)
177.64(18)
i1–Cd1–n1
i1–Cd1–n7
i2–Cd1–n1
i2–Cd1–n7
n1–Cd1–n4
n1–Cd1–n10
n4–Cd1–n10
92.70(12)
87.13(12)
92.06(12)
88.66(12)
179.08(16)
85.76(18)
93.69(18)
Cd1–o1
2.276(3)
Cd1–o1W
2.255(4)
Cd1–o2W
Cd1–o4W
2.343(3)
2.300(4)
Cd1–o3W
Cd1–n1
2.309(4)
2.295(4)
o1–Cd1–o1W
o1–Cd1–o3W
o1–Cd1–n1
o1W–Cd1–o3W
o1W–Cd1–n1
o2W–Cd1–o4W
o3W–Cd1–o4W
o4W–Cd1–n1
3
93.00(15)
90.68(14)
99.49(15)
90.18(14)
167.49(16)
95.70(14)
178.90(14)
89.97(14)
o1–Cd1–o2W
o1–Cd1–o4W
o1W–Cd1–o2W
o1W–Cd1–o4W
o2W–Cd1–o3W
o2W–Cd1–n1
o3W–Cd1–n1
171.13(14)
88.22(14)
79.10(14)
89.79(14)
85.38(14)
88.49(14)
90.29(14)
Cd1–Cl1
2.6185(19)
2.332(2)
93.23(4)
180.00
89.59(4)
86.77(4)
92.26(6)
Cd1–o1W
2.364(2)
Cd1–n1
Cl1–Cd1–o1W
Cl1–Cd1–Cl1a
Cl1–Cd1–n1a
o1W–Cd1–Cl1a
o1W–Cd1–n1a
4
Cl1–Cd1–n1
90.41(4)
180.00
87.74(6)
180.00
n1–Cd1–n1a
o1W–Cd1–n1
o1W–Cd1–o1Wa
Cd1–Br1
Cd1–n1
2.7213(2)
2.3434(16)
89.23(4)
180.00
90.61(4)
90.77(4)
90.82(5)
Cd1–o1W
2.3656(15)
Br1–Cd1–o1W
Br1–Cd1–Br1b
Br1–Cd1–n1b
o1W–Cd1–Br1b
o1W–Cd1–n1b
5
i1–Cd1
Cd1–o1W
i1–Cd1–o1W
i1–Cd1–n1
i1–Cd1–i1c
i1–Cd1–o1Wc
i1–Cd1–n1c
Br1–Cd1–n1
89.39(4)
180.00
89.18(5)
180.00
n1–Cd1–n1b
o1W–Cd1–n1
o1W–Cd1–o1Wb
2.885(2)
2.355(3)
90.07(5)
89.55(5)
180.00
89.93(5)
90.45(5)
Cd1–n1
2.377(3)
o1W–Cd1–n1
n1–Cd1–n1c
89.12(7)
180.00
180.00
o1W–Cd1–o1Wc
o1W–Cd1–n1c
90.88(7)
symmetry codes: a1 − x, 1 − y, 1 − z. b−x, 1 − y, 1 − z. c−x, 1 − y, 1 − z.
3. Results and discussion
3.1. Description of the crystal structures
3.1.1. Structure description of [CdI2(3-PyBim)](H2O)3 (1)
The results of X-ray crystallographic analysis reveal that 1 is mononuclear, crystallizing in
the triclinic P-1 space group. One Cd, four 3-PyBim ligands, two iodides, and three water
molecules exist in the asymmetric unit. As illustrated in Figure 1(a), Cd is six-coordinate with
a distorted octahedral coordination environment surrounded by four nitrogens from four
3-PyBim ligands and two iodides. The bond distances of Cd-N in 1 vary from 2.422(5) to

JOURNAL OF COORDINATION CHEMISTRY
7
Table 3. hydrogen bond geometries in the crystal structure of 1–5.
D–H⋯Aa
H⋯A (Å)
D⋯A (Å)
D–H⋯A (°)
Complex
1
o1W–h1⋯n2
o1W–h2⋯n6a
n2–h2⋯o1W
o2W–h3⋯n11
o2W–h4⋯n8b
n6–h6⋯o1Wa
n9–h9⋯n12c
n11–h11⋯o2W
C1–h1a⋯o1W
C3–h37⋯o2W
2.00
1.93
1.91
2.01
1.90
1.75
2.02
1.94
2.45
2.43
2.755(7)
2.728(7)
2.755(7)
2.764(7)
2.713(7)
2.728(7)
2.855(7)
2.764(7)
3.362(8)
3.351(8)
148
155
162
148
160
151
167
149
166
168
2
n3–h3⋯o4d
o1W–h11⋯o2e
o1W–h12⋯n2e
o2W–h21⋯o2e
o2W–h22⋯o3f
o3W–h31⋯o3
o3W–h32⋯o1e
o4W–h41⋯o4g
o4W–h42⋯o2f
C4–h4⋯o3Wh
C5–h5⋯o2W
1.99
2.30
1.85
1.96
1.93
2.03
1.97
2.03
1.88
2.41
2.48
2.51
2.861(6)
3.038(6)
2.691(5)
2.759(6)
2.759(5)
2.799(6)
2.772(6)
2.860(6)
2.722(6)
3.263(5)
3.140(6)
3.262(7)
168
147
179
158
172
153
161
168
177
150
127
136
C10–h10⋯o3f
3
4
5
o1W–h1⋯n3i
n2–h2⋯Cl1j
1.95
2.31
2.59
2.798(3)
3.170(3)
3.438(3)
172
164
166
o1W–h3⋯Cl1k
o1W–h1Wa⋯n3l
o1W–h1WB⋯Br1m
n2–h2a⋯Br1l
1.97
2.76
2.5
2.791(3)
3.4869(14)
3.3768(18)
172
150
161
o1W–h1Wa⋯n3n
o1W–h1WB⋯i1o
n2–h2a⋯i1n
1.96
2.91
2.73
2.807(3)
3.666(3)
3.593(3)
173
150
160
symmetry codes: a1 − x, −y, 1 − z. b1 − x, 1 − y, 1 − z. c−x, 1 − y, 1 − z. dx, 1/2 − y, 1/2 + z. e1 − x, 1/2 + y, 1/2 − z. f−1 + x, y, z.
g1 − x, −1/2 + y, 1/2 − z. h1 − x, 1 − y, 1 − z. i2 − x, −y, 1 − z. j1 − x, −y, 1 − z. kx, y,−1 + z. l−1 + x, y, z. m−x, 1/2 + y, 3/2 − z.
n−1 − x, 1 − y, 1 − z. o−x, 1/2 + y, 3/2 − z. p−1 − x, 1 − y, 1 − z.
2.455(5) Å; the bond lengths of Cd-I are 2.9076(6) to 2.9134(6) Å, in agreement with those
published previously [28].
As illustrated in Figure 1(b), one O–H⋯N intermolecular hydrogen bond was formed
between the free water molecules and nitrogens from the imidazole groups (O1W–H1⋯N2,
O1W–H2⋯N6a, O2W–H3⋯N11 and O2W–H4⋯N8b distances of 2.755(7), 2.728(7), 2.764(7)
and 2.713(7) Å, respectively, a1 − x, −y, 1 − z, b1 − x, 1 − y, 1 − z), through which a 1-D supra-
molecular chain is generated.
There also exist three kinds of intermolecular hydrogen bonds in 1: (i) N–H⋯O intermo-
lecular hydrogen bonds form between nitrogens of imidazole and free water molecules
(N2–H2⋯O1W, N6–H6⋯O1Wa and N11–H11⋯O2W distances of 2.755(7), 2.728(7) and
a
2.764(7) Å, respectively, 1 − x, −y, 1 − z); (ii) The N–H⋯N intermolecular hydrogen bond
comes from nitrogens of imidazoles and other nitrogens of imidazoles (N9–H9⋯N12c dis-
c
tance of 2.855(7) Å, −x, 1 − y, 1 − z); (iii) Intermolecular hydrogen bonds originate from
carbons of pyridine groups and free water molecules (C1–H1A⋯O1W and C3–H37⋯O2W
distances of 3.362(8) and 3.351(8) Å, respectively). The inter-hydrogen bonds alternate and

8
J.-H. WANG ET AL.
Table 4. Weak π⋯π packing interactions for 1–5.
Complexes
Distance (Å)
Average distance (Å)
1i
Cg(12)⋯Cg(5)a
Cg(5)⋯Cg(12)a
2ii
3.797(4)
3.797(4)
3.797
Cg(1)⋯Cg(1)c
Cg(1)⋯Cg(2)b
Cg(1)⋯Cg(3)c
Cg(2)⋯Cg(1)b
Cg(2)⋯Cg(3)b
Cg(3)⋯Cg(1)c
Cg(3)⋯Cg(2)b
3iii
3.359(3)
3.422(3)
3.544(3)
3.422(3)
3.785(3)
3.544(3)
3.785(3)
3.552
Cg(1)⋯Cg(1)d
Cg(2)⋯Cg(3)e
Cg(2)⋯Cg(3)d
Cg(3)⋯Cg(2)d
Cg(3)⋯Cg(2)d
4iv
3.566(3)
3.649(3)
3.594(3)
3.649(3)
3.594(3)
3.610
3.680
Cg(1)⋯Cg(1)f
Cg(2)⋯Cg(3)e
Cg(2)⋯Cg(3)f
Cg(3)⋯Cg(2)e
Cg(3)⋯Cg(2)f
5v
3.5679(12)
3.6813(12)
3.7347(12)
3.6813(12)
3.7347(12)
Cg(1)⋯Cg(1)i
Cg(2)⋯Cg(3)h
Cg(3)⋯Cg(2)i
3.715(3)
3.783(3)
3.783(3)
3.760
a
c
e
f
symmetry codes: −x, 1 − y, 1 − z. b1 − x, −y, 1 − z. 2 − x, −y, 1 − z. d1 − x, −y, −z. 2 − x, −y, −z. −x, 1 − y, 2 − z. g1 − x,
1 − y, 2 − z. h−x, 1 − y, 2 − z. i1 − x, 1 − y, 2 − z. ithe rings Cg(5) and Cg(2) are expressed by n(1)–C(1)–C(2)–C(3)–(4)–C(5)
and C(43)–C(44)–C(45)–C(46)–C(47)–C(48), respectively. iithe rings Cg(1), Cg(2), and Cg(3) consisted of n(2)–C(6)–n(3)–
C(12)–C(7), n(1)–C(1)–C(2)–C(3)–(4)–C(5), and C(7)–C(8)–C(9)–C(10)–C(11)–C(12), respectively. iiithe rings Cg(1), Cg(2),
and Cg(3) denote n(2)–C(6)–n(3)–C(12)–C(7), n(1)–C(1)–C(2)–C(3)–(4)–C(5), and C(7)–C(8)–C(9)–C(10)–C(11)–C(12),
respectively. ivthe rings Cg(1), Cg(2), and Cg(3) contain n(2)–C(6)–n(3)–C(12)–C(7), n(1)–C(1)–C(2)–C(3)–(4)–C(5),
and C(7)–C(8)–C(9)–C(10)–C(11)–C(12), respectively. vthe rings Cg(1), Cg(2), and Cg(3) consisted of n(2)–C(6)–n(3)–
C(12)–C(7), n(1)–C(1)–C(2)–C(3)–(4)–C(5), and C(7)–C(8)–C(9)–C(10)–C(11)–C(12), respectively.
consolidate the stacked arrangement leading to a two-dimensional layer along the ab plane
(Figure 1(c)).
Weak C–H⋯π interactions occur between carbons from phenyl groups and other phenyls
(C9–H9A⋯π(C19-C24), C21–H21A⋯π(C43-C48), C34–H34A⋯π(N7-C12) and C46–H46A⋯π(C31-C36) with
distances of 3.621(7), 3.576(8), 3.845(8), and 3.611(8) Å, respectively). Consequently, a 3-D
supramolecular architecture is constructed through these hydrogen bonding and weak
packing interactions (Figure 1(d)).
3.1.2. Structure description of [Cd(SO4)(3-PyBim)(H2O)4] (2)
When changing from CdI2 to Cd(SO4), 2 possessing a mononuclear structure was obtained.
Complex 2 crystallizes in the monoclinic space group P21/c. As illustrated in Figure 2(a), the
asymmetric unit of 2 is composed of one Cd(II), one 3-PyBim ligand, one sulfate, and four
coordinated waters. The coordination geometry around Cd(II) is six coordinate with a dis-
torted octahedral geometry by one nitrogen from a pyridine ring and five oxygens from one
sulfate and four different water molecules. The Cd-O bond distances in 2 are 2.255(4)-2.343(3)
Å; the Cd-N bond length is 2.295(4) Å, all in agreement with those published previously [28].

JOURNAL OF COORDINATION CHEMISTRY
9
Figure 1. (a) a perspective view of the coordination geometry of Cd in 1. (b) a one-dimensional chain
through hydrogen bonds along the b axis. (c) a two-dimensional layer along the ab plane in 1. (d) the
packing diagram of 1.

10
J.-H. WANG ET AL.
Figure 2. (a) a perspective view of the coordination geometry of Cd in 2. (b) a one-dimensional chain
through hydrogen bonds along the c axis. (c) a two-dimensional layer along the bc plane in 2. (d) the
topology structure of 2.

JOURNAL OF COORDINATION CHEMISTRY
11
The supramolecular structure depends on many kinds of hydrogen bonding interactions.
As illustrated in Figure 2(b), one hydrogen bond is generated through the nitrogens from
imidazole and the oxygens from sulfate (N3–H3⋯O4d distance of 2.861(6) Å, dx, 1/2 − y,
1/2 + z), through which a 1-D supramolecular chain is generated.
Additionally, hydrogen bonding occurs between oxygens from sulfates and nitrogens
from imidazole (O1W–H12⋯N2e distance of 2.691(5) Å, e1 − x, 1/2 + y, 1/2 − z). Thus, a 2-D
supramolecular layer is further generated through these hydrogen bonding interactions
(Figure 2(c)).
Apart from these interactions, there also exist other weak hydrogen bonding interactions
and weak packing interactions, which consolidate the stacked arrangement leading to a 3-D
supramolecular architecture. There exist three kinds of weak hydrogen bonding interactions:
(i) the coordinated water molecules and coordinated sulfate (O1W–H11⋯O2e, O2W–
H21⋯O2e, O2W–H22⋯O3f, O3W–H31⋯O3, O3W–H32⋯O1e, O4W–H41⋯O4g and O4W–
H42⋯O2f distances of 2.759(6), 2.759(5), 2.799(6), 2.772(6), 2.860(6), 2.722(6), and 3.038(6)
Å, respectively, e1 − x, 1/2 + y, 1/2 − z. f−1 + x, y, z and g1 − x, −1/2 + y, 1/2 − z); (ii) carbons of
pyridine rings and coordinated water (C4–H4⋯O3Wh and C5–H5⋯O2W distances of 3.263(5)
and 3.140(6) Å, respectively, h1 − x, 1 − y, 1 − z); (iii) carbons of phenyl rings and oxygens of
coordinated sulfate (C10–H10⋯O3i distance of 3.262(7) Å, i2 − x, −y, 1 − z). There also exist
a series of weak π⋯π packing interactions (Cg(1)⋯Cg(1)c, Cg(1)⋯Cg(2)b, Cg(1)⋯Cg(3)c,
Cg(2)⋯Cg(1)b, Cg(2)⋯Cg(3)b, Cg(3)⋯Cg(1)c, and Cg(3)⋯Cg(2)b distances of 3.359(3),
b
3.422(3), 3.544(3), 3.422(3), 3.785(3), 3.544(3), and 3.785(3) Å, respectively, 1 − x, −y, 1 − z
c
and 2 − x, −y, 1 − z. Cg(1), Cg(2), and Cg(3) are indicated as imidazole ring, pyridine ring,
and benzene ring, respectively) (Figure 2(d), Table 3). Consequently, through these hydrogen
bonding and weak packing interactions, a 3-D supramolecular architecture is constructed
(Figure 2(d)).
3.1.3. Structure description of [CdCl2(4-PyBim)2(H2O)2] (3)
Single-crystal X-ray analysis reveals that 3 is a mononuclear structure which crystallizes in
the form of the centrosymmetric space group P−1. As shown in Figure 3(a), the asymmetric
unit contains one Cd(II), one 4-PyBim ligand, one coordinated water, and one chloride. Cd1
is six-coordinate with two nitrogens from two 4-PyBim ligands, two oxygens from two water
molecules, and two chlorides in a slightly distorted octahedral configuration. The bond
distances of Cd–Cl, Cd–O, and Cd–N in 3 are 2.6185(19), 2.364(2), and 2.332(2) Å, respectively,
in agreement with those published previously [28].
The supramolecular structure mainly depends on many hydrogen bonding interactions
originating from coordinated waters as donor/acceptors, nitrogens of the imidazole rings
and coordinated chlorides. There are three kinds of intermolecular hydrogen bonds in 3:
(i) intermolecular hydrogen bonding between coordinated water and coordinated chlorides
(O1W–H3⋯Cl1k, 3.438(3) Å, k−1 + x, y, z), generating a 1-D supramolecular chain along the
a axis in 3 (Figure 3(b)); (ii) intermolecular hydrogen bonding between coordinated water
i
and nitrogens from imidazole (O1W–H1⋯N3i 2.798(3) Å, 1 − x, −y, 1 − z.). Thus, a two-di-
mensional supramolecular layer is formed by this kind of hydrogen bonding on the basis of
j
1-D supramolecular chains in 3 (Figure 3(c)); (iii) The N2–H2⋯Cl1j (3.170(3) Å, x, y, −1 + z)
intermolecular hydrogen bonding comes from nitrogens of the imidazole rings and coordi-
nated chlorides. The supramolecular interactions are propitious to form a 3-D supramolecular
architecture via weak hydrogen bonding interactions mentioned above (Figure 3(d)).

12
J.-H. WANG ET AL.
Figure 3. (a) a perspective view of the coordination geometry of Cd in 3. (b) a one-dimensional chain
through hydrogen bonds along the a axis. (c) a two-dimensional layer along the ab plane in 3. (d) the
packing diagram of 3.

JOURNAL OF COORDINATION CHEMISTRY
13
There also exist two kinds of weak π⋯π packing interactions between the aromatic rings.
One occurs between pyridine groups and benzene (3.594(3) and 3.649(3) Å) and another
between two imidazole groups (3.5679(12) Å). These weak packing interactions consolidate
a three-dimensional supramolecular framework (Figure 3(d)).
3.1.4. Structure description of [CdBr2(4-PyBim)2(H2O)2] (4)
When CdCl2 was changed to CdBr2, 4 crystallizes in the monoclinic space group P21/c.
Complex 4 is also mononuclear. As illustrated in Figure 4(a), the asymmetric unit of 5 has
one Cd(II), one 4-PyBim ligand, one bromide, and one coordinated water. The coordination
geometry around Cd(II) is six coordinate with a distorted octahedral geometry, surrounded
by two nitrogens from two different 4-PyBim ligands, two oxygens from two coordinated
waters and two bromides. The Cd-Br, Cd-O, and Cd-N bond distances in 4 are 2.7213(2),
2.3656(15), and 2.3434(16) Å, respectively, in agreement with those published previously
[28].
As illustrated in Figure 4(b), a hydrogen bond is generated through the coordinated water
l
and bromides (O1W–H1WB⋯Br1l distance of 3.4869(14) Å, −1 − x, 1 − y, 1 − z), through
which a 1-D supramolecular chain is generated along the a axis.
Apart from the O–H⋯Br intermolecular hydrogen bond, there also exist two weak π⋯π
packing interactions between aromatic rings. One originates from the pyridine and benzene
(3.6813(12) and 3.7347(12) Å) and another from two imidazole groups (3.5679(12) Å). These
weak π⋯π packing interactions and the O–H⋯Br hydrogen bond lead to a 2-D supramo-
lecular layer (Figure 4(c)).
There exist two other kinds of weak hydrogen bonding interactions: (i) O1W-H1WA⋯N3l
l
(2.791(3) Å, −x, 1/2 + y, 3/2 − z) intermolecular hydrogen bonding between coordinated
l
water and nitrogen from imidazole; (ii) N2–H2A⋯Br1l (3.3768(18) Å, −x, 1/2 + y, 3/2 − z)
intermolecular hydrogen bonding between the coordinate bromides and nitrogens from
imidazole. These hydrogen-bonding patterns A–D (Acceptor–Donor) construct a 3-D supra-
molecular architecture in 4 (Figure 4(d)).
3.1.5. Structure description of [CdI2(4-PyBim)2(H2O)2] (5)
X-ray crystallographic analysis showed that 5 is also mononuclear, crystallizing in the
monoclinic space group P21/c. As illustrated in Figure 5(a), one Cd(II), one 4-PyBim
ligand, one iodide, and one coordinated water exist in the asymmetric unit. The coordi-
nation geometry around Cd(II) is six coordinate with a distorted octahedral geometry
from two nitrogens of two different 4-PyBim ligands, two oxygens from two coordinated
water molecules and two iodides (Figure 5(a)). The bond distances of Cd-O and Cd-N
are 2.355(3) and 2.377(3) Å, respectively, similar to those found in complexes reported
previously [28].
Similar to 4, a hydrogen bond is generated through the coordinated water molecule and
iodide (O1W–H1WB⋯I1n 3.666(3) Å, n−1 − x, 1 − y, 1 − z), through which a 1-D supramolecular
chain is generated along the crystallographic a axis (Figure 5(b)).
Two kinds of weak π⋯π packing interactions exist between the aromatic rings, one from
pyridine and benzene (3.783(3) Å) and another from two imidazole groups (3.715(3) Å). As
a result, a 2-D supramolecular layer based on these supramolecular interactions is con-
structed (Figure 5(c)).

14
J.-H. WANG ET AL.
Figure 4. (a) a perspective view of the coordination geometry of Cd in 4. (b) a one-dimensional chain
through hydrogen bonds along the a axis. (c) a two-dimensional layer along the ac plane in 4. (d) the
packing diagram of 4.

JOURNAL OF COORDINATION CHEMISTRY
15
Figure 5. (a) a perspective view of the coordination geometry of Cd in 5. (b) a one-dimensional chain
through hydrogen bonds along the a axis. (c) a two-dimensional layer along the ac plane in 5. (d) the
packing diagram of 5.

16
J.-H. WANG ET AL.
Two other hydrogen bonds are observed: (i) O1W–H1WA⋯N3n (2.807(3) Å, n−x, 1/2 + y,
3/2 − z) intermolecular hydrogen bond forms between the coordinated water and nitro-
n
gen from imidazole; (ii) N2–H2A⋯I1n (3.593(3) Å, −x, 1/2 + y, 3/2 − z) intermolecular
hydrogen bond between nitrogen from the imidazole rings and iodide. Consequently,
a 3-D supramolecular architecture is interestingly founded via the three types of hydro-
gen-bonded patterns A–D mentioned above and other weak packing interactions in 5
(Figure 5(d)).
3.2. Powder X-ray diffraction (XRD) patterns and thermogravimetic analyses (TGA)
To confirm the phase purity of the five complexes, the XRD patterns were recorded. Most of
the peak positions of the simulated and experimental patterns are in agreement with each
other (Figures S1–S5). The present results show that products are a pure phase.
To estimate the stability of the coordination architectures of 1–5, TGA were carried out.
The experiments were performed on powder samples of 1–5 under nitrogen with a heating
rate of 10 °C min−1 (Figures S6–S10 in the Supporting Information). Complex 1 lost its coor-
dinated water from room temperature to 136 °C (obsd 5.9%, calcd 4.50%). The anhydrous
compound begins to decompose at 247 °C, leading to formation of CdO as the residue (obsd
9.41%, calcd 10.69%). For 2, the first weight loss corresponding to release of coordinated
water is observed before 177 °C (obsd 13.85%, calcd 15.13%), and the organic components
were lost from 290 °C. The final residue of 22.98% (calcd 26.99%) is observed, which indicates
that formation of CdO is generated. TheTGA curve of 3 shows that the first weight loss occurs
from 70–241 °C (obsd 4.56%, calcd 5.90%), indicating that coordinated water molecules are
lost. Decomposition of the anhydrous compound occurs from 296 to 762 °C. The final weight
of 18.00% (cald 21.06%) is observed, corresponding to formation of cadmium oxide. For 4,
weight loss from 56 to 233 °C corresponds to loss of coordinated water (obsd 6.3%, calcd
5.3%); removal of the organic components occurs from 260 to 520 °C. The remaining weight
corresponds to CdO (obsd 12.78%, calcd 18.38%). Complex 5 lost its coordinated water
molecules from 68 to 172 °C (obsd 4.32%, cald 4.54%). The anhydrous compound begins to
decompose at 225 °C. The weight of the final compound is 11.57% (cald 16.20%), which can
tentatively be assigned to CdO.
3.3. Photoluminescent properties
In view of the excellent luminescent properties of d10 metal coordination complexes [29],
the solid state luminescence properties of 1–5 were studied at room temperature. The emis-
sion spectra have broad peaks with maxima at 404, 413, 451, 444, and 435 nm (λex = 280 nm)
for 1–5, respectively. To compare the emission bands for complexes, we have also investi-
gated the luminescence properties of the two free ligands in the solid state at room tem-
perature. As indicated in Figure 6(a) and (b), the emission maxima were observed at 417 and
540 nm for free 3-PyBim, 411 and 516 nm for 4-PyBim, and are attributed to the π*→π
transition. Compared with the emission peaks of free 3-PyBim, the emission maxima for 1
and 2 are blue-shifted about 4 and 13 nm, respectively. The present results could be assigned
to intra-ligand π*→π transition. In comparison with the emission peaks of free 4-PyBim,
those of 3–5 are red-shifted about 40, 33, and 24 nm, respectively, which may be ascribed
to the intra-ligand π*→π transition. Luminescence intensities of all the complexes are stronger

JOURNAL OF COORDINATION CHEMISTRY
17
100
80
60
40
20
0
3-PyBim
1
2
400
500
600
700
Wavelength (nm)
(a)
100
4-PyBim
3
4
5
80
60
40
20
0
400
500
600
700
Wavelength (nm)
(b)
40
30
20
10
0
1
2
3
4
5
-10
Coordination Complexes
(c)
Figure 6. fluorescence emission spectra of 3-PyBim, 4-PyBim and its complexes 1 and 2 (a), and 3–5 (b)
in the solid state at room temperature. (c) Comparison of emission maxima for 1–5.
than those of the free ligands, which could be a consequence of coordination of the ligand,
increasing the rigidity of the ligand, thereby reducing the loss of energy through a radia-
tionless pathway [30].

18
J.-H. WANG ET AL.
Table 5. Photoluminescent properties for 3-PyBim, 4-PyBim and 1–5.
a
Compounds
Emission maxima
∆
3-PyBim
417
404
413
411
451
444
435
1
−13
−4
2
4-PyBim
3
4
5
+40
+33
+24
a∆: the shift values for 3-PyBim, 4-PyBim and 1–5. the symbols‘−’ and‘+’ are represented as blue-shifted and red-shifted,
respectively.
Photoluminescent complexes with 3/4-PyBim have been investigated. Complexes such
as [Ag2(4-PyBim)2(H2O)2]SO4·H2O [21b], [Co(3-PyBim)2(H2O)2Mo6O20] [21c], [Cu2(CN)2(3-
PyBim)]n [21e], [Ag(4-PyBim)(H2O)(NO3)]n [21f] and [Cu2(SCN)2(4-PyBIm)]n [21g] display inter-
esting photoluminescent properties, with emission located at 540, 446, 440, 394, and 569 nm,
respectively, similar to those observed in the present work. Comparison with the photolu-
minsecent behaviors of ligands 3-PyBim and 4-PyBim, those of complexes are blue-shifted
and red-shifted in the present work.
The blue-shifted magnitude of 1 is much smaller than that of 2. The red-shifted extent
gradually decreases from 3 to 5. Consequently, we propose that when the electronegativity
of the coordinated atoms from the coordinated anions was increased, the blue/red-shift was
raised. To further investigate whether there exists a relationship between the structures and
the emission properties among these complexes, we examined the nature of the coordination
environment of Cd(II). As illustrated in the description of crystal structures for 1–5, there are
significant differences from the coordinated anions, SO24−, I−, Cl−, Br− and I− for 2, 1, 3, 4, and
5, respectively. In 2, there only exist nitrogens and oxygens. However, in 1, with coordinated
N and O, there is iodide. The extent of blue-shift for 2 is much stronger than that of 1 (Figure
6(c)). The electronegativity of oxygen in 2 is much higher than that of iodide in 1. We suggest
that the electronegativity of the coordinated atoms accounts for the extent of blue-shift but
also the shift is proportional to the electronegativity of the coordinated atoms. The interesting
results encourage us to further investigate whether there exists a structure-property rela-
tionship among 3–5 and the specific structure-activity relationship was also found among
these complexes. It is clear that there are different coordinated ions, chloride, bromide, and
iodide. Electronegativity decreases from Cl to I. The red-shifted values of luminescent prop-
erties for 3–5 are 40, 33, and 24 nm, respectively (Table 5 and Figure 6(c)). The present obser-
vation further confirmed the fact that the shift of photoluminescence is proportional to the
electronegativity of the coordinated atoms among these complexes. The observed blue- or
red-shift of the emission maximum may be tentatively attributed to the following reasons:
(i) after the ligands coordinated with metal ions, they may affect their lowest occupied molec-
ular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels; (ii) com-
plexes may have charge-transfer transitions between Cd(II) centers and ligands [21f,g].
3.4. Difference of the coordination modes between 3-PyBim and 4-PyBim
The N from pyridinyl group in the 3/4-PyBim binds monodentate to metal ions. The two
nitrogens of benzimidazole groups play a role as donor and acceptor for hydrogen bonds,
affecting the solid structures. To further investigate these coordination modes and hydrogen

JOURNAL OF COORDINATION CHEMISTRY
19
H-D
H-D
H-D
H-D
H
N
H
N
H
N
H
N
N
Cd
N
M
N
N
N
N
M
N
M
N
M
Cd
H-A
H-A
Scheme 2. the coordination modes for 3-PyBim and 4-PyBim.
bonds of 3/4-PyBim complexes, we summarize the structural features of reported complexes
with 3/4-PyBim ligands [21]. There exist three potential coordination sites in 3/4-PyBim
ligands (two nitrogens from benzimidazole and one nitrogen from pyridinyl ring). (i) In the
present work, the 3/4-PyBim ligands use N from pyridine to bind Cd(II) (Scheme 2), similar
with the coordination mode of 3/4-PyBim observed in ([Cu(3-PyBim)2(H2O)2](ClO4)2, [Co(3-
PyBim)2(H2O)4](NO3)2·(H2O)4, [Cu(4-PyBim)2(Cl)2](H2O)2, [Zn(4-PyBim)2(H2O)2(NO3)2], and
[Cu2(3-PyBim)2(OAc)4]) [21a]. As a result, these complexes display a zero-dimensional motif.
(ii) The ligands possess the‘end-on’binding with a hydrogen-bond donor (H-D) and acceptor
(H-A), comparable to reported results [21a]. These features provide weak interaction sites
for the construction of supramolecular architectures. In 1, two adjacent units are connected
by O-H⋯N hydrogen bonds between free water molecules and nitrogens from benzimida-
zole rings, resulting in a 1-D chain along the a axis. Similarly, in 2, N-H⋯O hydrogen bonds
are generated through nitrogens from benzimidazole and oxygens from sulfate, giving a
1-D chain. In 3–5, a 2-D supramolecular layer is formed by O-H⋯N hydrogen bonds between
coordinated water and nitrogens from the benzimidazole groups of these 1-D supramolec-
ular chains. Such results are also observed in other supramolecular assemblies [21a]. Finally,
a 3-D supramolecule is constructed by N-H⋯X (X = Cl, Br, I) hydrogen interactions on the
basis of a 2-D supramolecular layer. Apart from these hydrogen bond interactions, there
exist two kinds of weak π⋯π packing interactions between aromatic rings to construct a
2-D supramolecular layer. The coordination modes of 3/4-PyBim ligands are observed in
the present work and some reported complexes, which are listed in Scheme 2. We anticipate
other interesting coordination modes of 3/4-PyBim when more coordination complexes
with these ligands are explored.
4. Conclusion
We have prepared a set of Cd(II) coordination complexes that exhibit extended
three-dimensional structures supported by two N-heterocyclic ligands through self-assembly
under hydrothermal conditions. The photoluminescent properties can be tuned through
the electronegativity of the coordinated counterions, with their blue/red-shift of lumines-
cence decreased upon decrease of the electronegativity of the coordinated atoms. Further
development of metal complexes with interesting photoluminescent properties is underway
in our laboratory.
Acknowledgements
We thank Ms Min Liu, Ms Nan-Nan Sun, and Mr Dan Liu for helping with experiments. We also thank
the reviewers for giving many constructive comments.

20
J.-H. WANG ET AL.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the National Natural Science Foundation of China [grant number 21276149],
Shandong Distinguished Middle-agedYoung Scientist Encouragement and Reward Foundation [grant
number BS2011CL034], Program for Scientific Research InnovationTeam in Colleges and Universities of
Shandong Province, International Cooperation Project for the ExcellentYouth Scholars by Department
of Education of Shandong Province, the Project of Shandong Province Higher Educational Science and
Technology Program [grant number J09LB03].
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