Syntheses, structures, and properties of copper and cadmium complexes with quinoline-based benzimidazole

Article abstract of DOI:10.1080/00958972.2010.548862

A new tridentate ligand 2-((quinolin-8-yloxy)methyl)benzimidazole (L) and three coordination compounds, [CuLCl₂] (1), [CuL(H ₂O)(SO₄)· 2H₂O]_n (2), and {[Cd₂L₂Cl₄][CdLCl₂(H ₂O)]₂}·H₂O (3), have been synthesized and characterized. Single crystal structure analyses reveal extensive intermolecular hydrogen bonding, resulting in generation of 1-D-3-D supramolecular networks. Compounds 1 and 2 constitute the first examples of Cu complexes containing both 8-hydroxyquinoline and benzimidazole, while 3 represents the first Cd complex bearing this ligand. Complexes 1-3 show similar quasi-reversible electrochemical behaviors. Complex 2 exhibits a predominantly ferromagnetic interaction between copper centers, and 3 has good fluorescence and can be used as an optical material.

Full text of DOI:10.1080/00958972.2010.548862

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Syntheses, structures, and properties
of copper and cadmium complexes with
quinoline-based benzimidazole
Yong-Hong Wen a , Xing-Lei Xie a & Lei Wang a
a Key Laboratory of Eco-chemical Engineering, Ministry of
Education, College of Chemistry and Molecular Engineering,
Qingdao University of Science and Technology, Qingdao 266042,
People's Republic of China
Published online: 10 Jan 2011.
To cite this article: Yong-Hong Wen , Xing-Lei Xie & Lei Wang (2011) Syntheses, structures, and
properties of copper and cadmium complexes with quinoline-based benzimidazole, Journal of
Coordination Chemistry, 64:3, 459-472, DOI: 10.1080/00958972.2010.548862
To link to this article: http://dx.doi.org/10.1080/00958972.2010.548862
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Journal of Coordination Chemistry
Vol. 64, No. 3, 10 February 2011, 459–472
Syntheses, structures, and properties of copper and cadmium
complexes with quinoline-based benzimidazole
YONG-HONG WEN*, XING-LEI XIE and LEI WANG
Key Laboratory of Eco-chemical Engineering, Ministry of Education, College of Chemistry
and Molecular Engineering, Qingdao University of Science and Technology, Qingdao
266042, People’s Republic of China
(Received 25 September 2010; in final form 3 November 2010)
A new tridentate ligand 2-((quinolin-8-yloxy)methyl)benzimidazole (L) and three coordination
and
compounds,
[CuLCl2]
(1),
[CuL(H2O)(SO4) ꢀ 2H2O]n
(2),
{[Cd2L2Cl4][CdLCl2(H2O)]2} ꢀ H2O (3), have been synthesized and characterized. Single crystal
structure analyses reveal extensive intermolecular hydrogen bonding, resulting in generation of
1-D–3-D supramolecular networks. Compounds 1 and 2 constitute the first examples of Cu
complexes containing both 8-hydroxyquinoline and benzimidazole, while 3 represents the first
Cd complex bearing this ligand. Complexes 1–3 show similar quasi-reversible electrochemical
behaviors. Complex 2 exhibits a predominantly ferromagnetic interaction between copper
centers, and 3 has good fluorescence and can be used as an optical material.
Keywords: Copper complex; Cadmium complex; Fluorescence; Electrochemical property;
Magnetic property
1. Introduction
Benzimidazole-containing compounds has attracted attention since Hobrecker reported
synthesis of the first benzimidazole, 2,5-dimethylbenzimidazole, in 1872 [1, 2].
Investigation of the benzimidazole-containing compound complexes with transition
metals is one of the most important subjects in coordination chemistry, crystal
engineering, medicine, and material science owing to their fascinating structural
motifs [3] and characteristic properties such as luminescence [4, 5], catalysis [6, 7], and
antivirus activity [8–10]. Cu complexes [Cu(SO4)(pbbm)]n and {[Cu(Ac)2(pbbm)] ꢀ
CH3OH}n (pbbm ¼ 1,10-(1,5-pentanediyl)bis-1H-benzimidazole) are efficient homoge-
neous catalysts for oxidative coupling of 2,6-dimethylphenol [6], while Cu and Cd
complexes of several bis(benzimidazole) ligands have been examined as potential
models of structure and mobility of biological metal binding sites [3].
8-Hydroxyquinoline and its derivatives find wide application in coordination
chemistry [11], pharmaceutical chemistry [12–14], and materials chemistry [15]. The
syntheses and properties of 8-hydroxyquinoline derivatives and their complexes have
*Corresponding author. Email: yonghwen@163.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
DOI: 10.1080/00958972.2010.548862

460
Y.-H. Wen et al.
attracted much research [16]. 8-Hydroxyquinoline and benzimidazole are both
inexpensive and have large planar ꢀ-conjugated systems. However, compounds
containing both 8-hydroxyquinoline and benzimidazole have not been investigated.
In this article,
8-yloxy)methyl)benzimidazole
a
new tridentate ligand with N2O donor set 2-((quinolin-
(L) and three complexes, [CuLCl2] (1),
[CuL(H2O)(SO4) ꢀ 2H2O]n (2), and {[Cd2L2Cl4][CdLCl2(H2O)]2} ꢀ H2O (3), have been
synthesized and characterized by X-ray diffraction single crystal structure analyses,
elemental analyses, infrared (IR) spectra, electrochemical, magnetic, and fluorescence
properties.
2. Experimental
2.1. Materials and measurements
All commercially available reagents and chemicals were of analytical grade purity and
used without purification. Deionized water was obtained by passing distilled water
through a Barnstead E-pure 3-Module system. The C, H, and N contents were
determined using an Elementar Vario EL III analyzer. IR spectra were recorded from
KBr pellets by a Nicolet 510P FT–IR spectrometer. 1H-NMR spectra were recorded by a
Bruker Avance 500 MHz spectrometer with TMS as an internal standard. Fluorescence
measurements were made on a Hitachi F-4500 fluorescence spectrophotometer.
2.2. Synthesis
2.2.1. Synthesis of 2-((quinolin-8-yloxy)methyl)benzimidazole (L). 2-(Quinolin-
8-yloxy)acetic acid was synthesized by refluxing an aqueous solution of 8-hydro-
xyquinoline, 2-chloroacetic acid, and sodium hydroxide for 4 h, followed by
acidification with HCl to pH ¼ 2. A mixture of 2-(quinolin-8-yloxy)acetic acid
(10.16 g, 0.05 mol), benzene-1,2-diamine (5.41 g, 0.05 mol), and 6 mol Lꢁ1 HCl
(50 mL) was refluxed for 5 h and then cooled to room temperature. The reaction
mixture was poured into 200 mL of cold water. A large amount of precipitate appeared
when pH was adjusted to 8–9 by adding ammonia dropwise to the mixture. The
resulting solid was washed three times with cold water (3 ꢂ 10 mL) to obtain a crude
product. Recrystallization of the crude product in C2H5OH/CH3COCH3 (1 : 1) afforded
1
L as colorless crystals. Yield: 9.81 g, 71.3%; m.p.: 179–181ꢃC. H-NMR (500 MHz,
DMSO-d6, ꢁ, ppm): 12.84 (s, 1H, NH), 7.20–8.86 (m, 10H, Ph, and py), 5.54 (s, 2H,
OCH2). IR (KBr pellet, cmꢁ1): 3423s, 3286s, 3099m, 3018m, 2896m, 2847m, 2785m,
1619m, 1597w, 1572w, 1546w, 1504s, 1473m, 1459m, 1441s, 1424m, 1354m, 1319s,
1270vs, 1223w, 1116vs, 1088m, 1026w, 827m, 794m, 752vs, 696m, 640w, 590w, 492w,
and 437w. Anal. Calcd for C17H13N3O: C, 74.17; H, 4.76; and N, 15.26. Found: C,
74.25; H, 4.69; and N, 15.31.
2.2.2. Synthesis of [CuLCl2] (1). To a methanol solution (10 mL) of L (68.8 mg,
0.25 mmol) was added dropwise a methanol solution (5 mL) of CuCl2 ꢀ 2H2O (42.6 mg,
0.25 mmol). The mixture was stirred at room temperature for 5 h and then filtered to

Copper and cadmium complexes with quinoline-based benzimidazole
461
give a clear green solution. Green block crystals suitable for X-ray diffraction analysis
of 1 were obtained by slow evaporation of the solvent for 10 days. Yield: 72.7 mg, 71%.
IR (KBr pellet, cmꢁ1): 3430s, 3246s, 2922w, 2851w, 1637m, 1624m, 1589w, 1529w,
1506m, 1474m, 1457m, 1446m, 1377m, 1322m, 1264m, 1190w, 1133m, 1072w, 1044w,
1007w, 922w, 823w, 785w, 761m, 742m, 679m, 632m, 563w, 471w, 433w, and 420w.
Anal. Calcd for C17H13Cl2CuN3O: C, 49.83; H, 3.20; and N, 10.25. Found: C, 49.68;
H, 3.11; and N, 9.92.
.
2.2.3. Synthesis of [CuL(H2O)(SO4) 2H2O]n (2). To a methanol solution (10 mL) of
L (68.8 mg, 0.25 mmol) was added dropwise a methanol solution (5 mL) of
CuSO4 ꢀ 5H2O (62.4 mg, 0.25 mmol). The mixture was stirred at room temperature for
5 h. The precipitated complex was filtered, washed with methanol, and dried over P4O10
for 48 h. Yield: 91.6 mg, 75%. Blue rhombus crystals suitable for X-ray diffraction
analysis of 2 were obtained by slow evaporation of the DMSO/H2O (3 : 1) solution of
the complex for 15 days. IR (KBr pellet, cmꢁ1): 3544vs, 3401s, 3270s, 3059s, 2971s,
2920s, 2848m, 2793m, 1913w, 1871w, 1625w, 1594m 1542w, 1508vs, 1459m, 1444s,
1383w, 1365m, 1326w, 1260vs, 1224s, 1183m, 1127vs, 1055m, 1033m, 1014m, 899w,
851w, 785w, 742vs, 715w, 619w, 600w, and 557w. Anal. Calcd for C17H19CuN3O8S:
C, 41.76; H, 3.92; and N, 8.59. Found: C, 41.69; H, 3.90; and N, 8.52.
.
2.2.4. Synthesis of {[Cd2L2Cl4][CdLCl2(H2O)]2} H2O (3). A procedure similar to that
described for synthesis of 2 was carried out with L (68.8 mg, 0.25 mmol) and
CdCl2 ꢀ 2.5H2O (57.1 mg, 0.25 mmol). Yield: 85.0 mg, 70%. Colorless rhombus crystals
suitable for X-ray diffraction analysis of 3 were obtained by slow evaporation of the
DMSO/H2O (1 : 1) solution of the complex for 20 days. IR (KBr pellet, cmꢁ1): 3434s,
3283s, 3065w, 2934w, 1621w, 1595w 1584w, 1536w, 1508s, 1473s, 1455m, 1445m,
1379m, 1334m, 1323s, 1265m, 1215w, 1187m, 1128s, 1074w, 1042w, 1017w, 914w, 852w,
824m, 787w, 766m, 748s, 701w, 678m, 622m, 562w, 506w, 463w, and 439w. Anal. Calcd
for C68H58Cd4Cl8N12O7: C, 43.25; H, 3.10; and N, 8.90. Found: C, 43.30; H, 3.19; and
N, 8.82.
2.3. Electrochemical studies
All electrochemical experiments were performed with a CHI 832B electrochemical
analyzer (Shanghai CHI Instrument Company, China) using a three-electrode system
composed of a glassy carbon electrode (GCE, ’ ¼ 2.96 mm) as a working electrode,
Ag/AgCl/(saturated)KCl as a reference electrode, and Pt wire as an auxiliary electrode.
A 0.2 mol Lꢁ1 Britton–Robinson buffer solution (BR buffer, the mixture of 3.39 mL
85% H3PO4, 2.95 mL HOAc, and 3.0875 g H3BO3 was diluted to 250 mL, and adjusted
to pH 4.0 with 0.5 mol Lꢁ1 NaOH) was used. The pH was measured with a PHS-3D pH
meter (Shanghai LeiCi Device Works, Shanghai, China) with a combined glass–calomel
electrode. Cyclic voltammetry measurements were made on a GCE in BR buffer
(pH 4.0) at room temperature with a scan rate of 20–200 mV sꢁ1. The GCE was
polished successively with 0.3 and 0.05 mm Al2O3 slurry on emery paper. It was then
rinsed with doubly distilled water and sonicated in 1 mol Lꢁ1 HNO3, acetone and
doubly distilled water for 10 min, respectively. The solutions of complexes were

462
Y.-H. Wen et al.
Table 1. Crystal data and structure refinement information of 1–3.
Compounds
1
2
3
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C17H13Cl2CuN3O
409.74
113(2)
Triclinic
ꢀ
P1
C17H19CuN3O8S
488.95
294(2)
Monoclinic
P21/n
C68H58Cd4Cl8N12O7
1888.46
113(2)
Monoclinic
P21/c
ꢃ
˚
Unit cell dimensions (A, )
a
b
c
ꢃ
ꢄ
ꢅ
7.1565(14)
9.6969(19)
12.609(3)
103.38(3)
105.32(3)
103.72(3)
778.4(3), 2
1.748
10.7838(19)
14.040(2)
13.344(2)
90
113.39(2)
90
1854.4(6), 4
1.751
1.346
0.22 ꢂ 0.20 ꢂ 0.16
2.07–25.02
9342
19.664(4)
12.743(3)
14.508(3)
90
104.01(3)
90
3527.1(13), 2
1.778
1.555
0.12 ꢂ 0.10 ꢂ 0.04
1.92–25.02
19,694
3
˚
Volume (A ), Z
Calculated density (g cmꢁ3
)
Absorption coefficient, ꢆ (mmꢁ1
Crystal size (mm3)
)
1.755
0.10 ꢂ 0.08 ꢂ 0.06
1.76–25.02
4816
ꢇ range for data collection (ꢃ)
Reflections collected
Independent reflections
Data/parameters
2735 [R(int) ¼ 0.0332] 3255 [R(int) ¼ 0.0285] 6204 [R(int) ¼ 0.0633]
2735/217
1.003
3255/271
1.052
0.0294, 0.0753
0.0388, 0.0822
6204/451
1.157
0.0604, 0.1479
0.0731, 0.1556
Goodness-of-fit on F2
Ra, wRb [I 4 2ꢈ(I)]
0.0316, 0.0796
0.0388, 0.0828
Ra, wRb (all data)
b
2
1=2
aR ¼ ÆjjFoj ꢁ jFcjj=ÆjFoj. wR ¼ ½ÆwðF2o ꢁ Fc2Þ=ÆwðF2oÞ ꢄ
.
prepared by dissolution in an appropriate amount of DMSO and then mixing in
BR buffer.
2.4. Crystal structure determinations
Single crystal X-ray diffraction data of 1–3 were collected on a Bruker SMART 1000
˚
CCD diffactometer with graphite monochromated Mo-Ka radiation (ꢂ ¼ 0.71073 A)
using ! scan mode at 113(2), 294(2), and 113(2) K, respectively. Intensity data were
corrected for Lp factors and empirical absorption. The structures were solved by direct
methods and refined using full-matrix least-squares on F2 with SHELXTL program
package [17]. The metals were located from the E-map and other non-hydrogen atoms
were located with successive difference Fourier syntheses. The hydrogens were
generated in ideal positions. Anisotropic thermal parameters were applied to all
non-hydrogen atoms. Atomic scattering factors and anomalous dispersion corrections
were taken from the International Tables for X-ray Crystallography [18]. Experimental
details of the X-ray diffraction analyses of 1–3 are given in table 1. Selected bond
lengths and angles for 1–3 are listed in table 2.
3. Results and discussion
3.1. Syntheses and general properties
L was synthesized successfully by simple two-step reactions with 8-hydroxyquinoline as
starting material. The synthetic processes gave high yields. The reaction of L with metal

Copper and cadmium complexes with quinoline-based benzimidazole
463
ꢃ
˚
Table 2. Selected bond lengths (A) and angles ( ) for 1–3.
Complex 1
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–O(1)
2.004(2)
1.989(2)
2.228(2)
Cu(1)–Cl(1)
Cu(1)–Cl(2)
2.276(2)
2.300(1)
O(1)–Cu(1)–Cl(1)
O(1)–Cu(1)–Cl(2)
Cl(1)–Cu(1)–Cl(2)
134.70(6)
100.93(6)
124.36(4)
N(2)–Cu(1)–N(1)
N(2)–Cu(1)–Cl(2)
N(1)–Cu(1)–Cl(2)
147.68(9)
98.82(7)
99.43(8)
Complex 2
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–O(1)
N(1)–Cu(1)–O(1)
N(2)–Cu(1)–O(1)
N(1)–Cu(1)–O(6)
N(2)–Cu(1)–O(6)
O(3A)–Cu(1)–O(2)a
1.994(2)
1.963(2)
2.151(2)
78.39(7)
76.89(7)
103.82(8)
100.15(8)
171.37(8)
Cu(1)–O(2)
Cu(1)–O(3A)a
Cu(1)–O(6)
N(1)–Cu(1)–O(2)
N(1)–Cu(1)–O(3A)a
N(2)–Cu(1)–O(2)
N(2)–Cu(1)–O(3A)a
O(6)–Cu(1)–O(1)
2.295(2)
2.141(2)
2.021(2)
83.65(8)
88.18(8)
89.81(8)
98.78(8)
172.96(8)
Complex 3
Cd(1)–N(1)
Cd(1)–N(3)
Cd(1)–O(1)
Cd(1)–O(2)
Cd(1)–Cl(1)
Cd(1)–Cl(2)
N(1)–Cd(1)–Cl(2)
N(1)–Cd(1)–O(2)
N(3)–Cd(1)–Cl(2)
N(3)–Cd(1)–O(2)
Cl(1)–Cd(1)–O(1)
N(3)–Cd(1)–Cl(1)
O(2)–Cd(1)–Cl(1)
N(1)–Cd(1)–Cl(1)
Cl(1)–Cd(1)–Cl(2)
2.263(5)
2.322(5)
2.500(4)
2.428(4)
2.465(2)
2.671(2)
90.3(1)
86.3(2)
88.8(1)
83.5(2)
174.1(1)
106.9(1)
94.3(1)
117.4(1)
100.09(5)
Cd(2)–N(4)
Cd(2)–N(6)
Cd(2)–O(3)
Cd(2)–Cl(3)
2.270(5)
2.312(6)
2.481(5)
2.550(2)
2.488(2)
2.929(2)
67.3(2)
Cd(2)–Cl(4)
Cd(2)–Cl(4A)b
N(4)–Cd(2)–O(3)
N(6)–Cd(2)–O(3)
N(4)–Cd(2)–Cl(4)
N(6)–Cd(2)–Cl(4)
Cl(3)–Cd(2)–Cl(4A)b
N(4)–Cd(2)–Cl(3)
N(6)–Cd(2)–Cl(3)
O(3)–Cd(2)–Cl(3)
Cl(4)–Cd(2)–Cl(3)
66.9(2)
120.1(2)
102.4(1)
172.98(8)
93.9(1)
94.0(1)
93.4(1)
102.12(8)
b
Symmetry codes: ax ꢁ 1/2, ꢁy þ 1/2, z ꢁ 1/2; ꢁx þ 1, ꢁy þ 1, ꢁz.
salts afforded three different complexes, [CuLCl2] (1), [CuL(H2O)(SO4) ꢀ 2H2O]n (2),
and {[Cd2L2Cl4][CdLCl2(H2O)]2} ꢀ H2O (3), depending on the counteranions or on the
metal cations in the metal salts. Complex 1 was obtained when CuCl2 ꢀ 2H2O was used,
while polynuclear 2 was obtained using CuSO4 ꢀ 5H2O; tetranuclear 3 was obtained
when CdCl2 ꢀ 2.5H2O was used instead of CuCl2 ꢀ 2H2O. All three complexes are stable
crystalline solids and can be stored in air at room temperature for a long time. These
complexes are soluble in CH3CN, DMF, and DMSO and slightly soluble in methanol
and acetone. IR spectra of ligand and complexes show the N–H characteristic
absorptions at 3246–3286 cmꢁ1, indicating that imidazole molecules are coordinated
through tertiary nitrogen to metal. This is in agreement with the single crystal structure
analyses.
3.2. Crystal structure of [CuLCl2] (1)
The molecular structure of 1 is shown in figure 1(a). In 1, five-coordinate Cu(II) has
approximately trigonal bipyramidal geometry. The equatorial positions are occupied by

464
Y.-H. Wen et al.
Figure 1. (a) The molecular structure of 1 with the atomic numbering scheme. (b) The coordination
polyhedron of Cu2þ in 1 with copper deviating from the N2OCl coordination plane and toward the elongated
apical Cl(2).
Figure 2. 2-D net structure of 1 along the b-axis constructed by hydrogen bonds.
O1 of L and two chlorides with the sum of the angles O(1)–Cu(1)–Cl(1), O(1)–Cu(1)–
Cl(2), and Cl(1)–Cu(1)–Cl(2) being 359.99ꢃ. The axial positions are occupied by two
benzimidazole nitrogens with the N(1)–Cu(1)–N(2) angle of 147.68(9)ꢃ. The bond
˚
˚
lengths, Cu–N 2.004(2) and 1.989(2) A, Cu–Cl 2.276(2) and 2.300(1) A, and Cu–O
˚
2.228(2) A, are within normal ranges for those in similar complexes [3, 19–22]. However,
the N(1)–Cu(1)–N(2) angle of 147.68(9)ꢃ deviates from the ‘‘ideal’’ value of 180ꢃ [23]
and the trigonality index ꢉ of 0.22 is close to the ꢉ value of zero for a perfect square
pyramidal [24], so the coordination geometry around copper is intermediate between
trigonal bipyramidal and square pyramidal geometries and is best described as trigonal
˚
bipyramidal distorted square-based pyramidal [20, 21] with copper displaced 0.639 A
above the N2OCl coordination plane and toward the elongated apical Cl(2) (figure 1b).
The dihedral angle between quinoline and benzimidazole rings in 1 is 14.12(9)ꢃ.
There exist different types of hydrogen bonds in 1. Intermolecular
N(3)–H(3A) ꢀ ꢀ ꢀ Cl(1) hydrogen bonds connect the complex into a head-to-tail dimer
[CuLCl2]2. Intermolecular N(3)–H(3A) ꢀ ꢀ ꢀ Cl(2) hydrogen bonds connect dimers into
1-D chain structures constructed by [CuLCl2]2 as building unit. Finally, these 1-D chain
structures are linked by intermolecular C(2)–H(2) ꢀ ꢀ ꢀ Cl(1) hydrogen bonds forming a
2-D net structure (figure 2). In 1, there are two types of bifurcated hydrogen bonds:
N(3)–H(3A) ꢀ ꢀ ꢀ Cl(1)/Cl(2), where H(3A) was shared by Cl(1) and Cl(2) to form a
tricentered hydrogen bond, and N(3)–H(3A)/C(2)–H(2) ꢀ ꢀ ꢀ Cl(1), two donors H(3A)

Copper and cadmium complexes with quinoline-based benzimidazole
465
ꢃ
˚
Table 3. Hydrogen bond data (A) and ( ) for 1–3.
D–H ꢀ ꢀ ꢀ A
d(D–H)
d(H ꢀ ꢀ ꢀ A)
d(D ꢀ ꢀ ꢀ A)
ffDHA
Complex 1
N(3)–H(3A) ꢀ ꢀ ꢀ Cl(1)a
N(3)–H(3A) ꢀ ꢀ ꢀ Cl(2)b
C(2)–H(2) ꢀ ꢀ ꢀ Cl(1)c
0.90
0.90
0.93
2.58
2.69
2.82
3.227(2)
3.341(3)
3.749(3)
129.4
130.1
177.2
Complex 2
O(6)–H(6A) ꢀ ꢀ ꢀ O(5)
O(6)–H(6B) ꢀ ꢀ ꢀ O(7)d
N(3)–H(3A) ꢀ ꢀ ꢀ O(4)e
O(7)–H(7A) ꢀ ꢀ ꢀ O(8)f
O(7)–H(7B) ꢀ ꢀ ꢀ O(5)g
O(8)–H(8A) ꢀ ꢀ ꢀ O(4)h
C(3)–H(3) ꢀ ꢀ ꢀ O(2)h
C(7)–H(7) ꢀ ꢀ ꢀ O(7)
0.85
0.86
0.89
0.85
0.85
0.86
0.93
0.93
1.88
1.83
1.80
2.03
1.96
1.92
2.52
2.43
2.714(3)
2.681(3)
2.690(3)
2.852(4)
2.813(3)
2.749(3)
3.356(3)
3.343(4)
164.9
170.1
179.0
164.1
171.6
162.8
149.0
166.1
Complex 3
O(2)–H(2B) ꢀ ꢀ ꢀ Cl(2)i
N(2)–H(2C) ꢀ ꢀ ꢀ Cl(2)j
O(4)–H(4A) ꢀ ꢀ ꢀ N(5)k
O(4)–H(4A) ꢀ ꢀ ꢀ Cl(3)l
N(5)–H(5A) ꢀ ꢀ ꢀ Cl(3)m
C(29)–H(29) ꢀ ꢀ ꢀ Cl(1)n
0.85
0.86
0.86
0.86
0.86
0.93
2.78
2.35
2.54
2.75
2.64
2.74
3.230(4)
3.178(6)
3.302(10)
3.302(11)
3.346(8)
3.666(8)
114.9
160.7
148.0
123.0
140.7
174.0
a
b
c
Symmetry codes: ꢁx þ 1, ꢁy þ 1, ꢁz þ 1; ꢁx þ 2, ꢁy þ 1, ꢁz þ 1; ꢁx þ 1,ꢁy þ 1, ꢁz þ 2; dx þ 1/2, ꢁy þ 1/2, z ꢁ 1/2;
e
j
f
h
ꢁx þ 3/2, y þ 1/2, ꢁz þ 3/2; ꢁx þ 1/2, y þ 1/2, ꢁz þ 3/2; gx ꢁ 1, y, z; ꢁx þ 3/2, y ꢁ 1/2, ꢁz þ 3/2; ix, ꢁy þ 1/2, z þ 1/2;
k
l
m
n
ꢁx þ 2, y ꢁ 1/2, ꢁz þ 1/2; ꢁx þ 1, ꢁy, ꢁz þ 1; x, ꢁy þ 1/2, z þ 1/2; ꢁx þ 1, y ꢁ 1/2, ꢁz þ 1/2; ꢁx þ 2, ꢁy þ 1, ꢁz þ 1.
and H(2) share one acceptor Cl(1) to form another tricentered hydrogen bond.
Hydrogen bond data are shown in table 3. In addition, the crystal packing exhibits ꢀ–ꢀ
stacking interactions. The short centroid–centroid distances between the imidazole rings
˚
of the neighboring molecules are 3.396(2) A, and those between pyridine and benzene
˚
rings in quinoline of the neighboring molecules 3.691(2) A.
.
3.3. Crystal structure of [CuL(H2O)(SO4) 2H2O]n (2)
The molecular structure of 2 is shown in figure 3. In 2, each Cu(II) is six-coordinate by
two nitrogens from L and four oxygens, one from L, one from a crystal water, and two
from two different sulfates. All coordinated bond lengths show normal values and are
comparable to those in 1 and in the other related compounds [3, 19–22]. The
coordination geometry around Cu is best described as octahedral. The equatorial
positions are occupied by O(1), O(6), N(1), and N(2) with the sum of the angles
N(1)–Cu(1)–O(1), N(2)–Cu(1)–O(1), N(1)–Cu(1)–O(6), and N(2)–Cu(1)–O(6) being
359.25ꢃ, and the axial positions by O(2) and O(3A) with O(2)–Cu(1)–O(3A) angle being
171.36(8)ꢃ. The dihedral angle between quinoline ring and benzimidazole ring is
10.41(8)ꢃ in 2. Complex 2 is linked by bridging bidentate sulfates to form a 1-D infinite
˚
chain (figure 4a). The distance of two neighboring Cu’s in the chain is 6.718 A, while the
˚
˚
distances of two neighboring Cu’s between the chains are 7.886 A and 8.727 A. The 1-D
chains are connected by short aromatic ring ꢀ–ꢀ stacking (figure 4a) and intermolecular
hydrogen bond interactions (figure 4b) to form a 3-D supramolecular structure. The
˚
distances between aromatic rings in neighboring molecules are from 3.307 to 3.446 A.

466
Y.-H. Wen et al.
Figure 3. The molecular structure of 2 showing the atom labeling scheme. Hydrogens are omitted for clarity.
O3A is related to O3 by the symmetry operator (x ꢁ 1/2, ꢁy þ 1/2, z ꢁ 1/2).
Figure 4. (a) The 1-D infinite chain structure of 2 showing the ꢀ–ꢀ stacking interactions among the aromatic
rings. The hydrogens and solvent molecules are omitted for clarity. (b) The hydrogen bond interactions
between the 1-D chains in 2. Waters are shown in ball and stick style, and the hydrogen bonds are shown as
dashed lines for clarity.
Three types of hydrogen bonds are found in 2: namely, O–H ꢀ ꢀ ꢀ O (O ꢀ ꢀ ꢀ O ¼ 2.681(3)–
˚
˚
2.852(4) A), N–H ꢀ ꢀ ꢀ O (N ꢀ ꢀ ꢀ O ¼ 2.690(3) A), and C–H ꢀ ꢀ ꢀ O (C ꢀ ꢀ ꢀ O ¼ 3.343(4)–
˚
3.356(3) A) (table 3).
.
3.4. Crystal structure of {[Cd2L2Cl4][CdLCl2(H2O)]2} H2O (3)
The asymmetric unit of 3 contains one half-molecule, the other half being related by a
crystallographic center of symmetry (figure 5), except for the uncoordinated crystal
water because the site occupancy factors of all atoms in the crystal water are 0.5. There
exist two different kinds of cadmium(II) in 3. Cd(1) is six-coordinate by two nitrogens
from L, two chlorides and two oxygens, one from L, and another from water. The
coordination geometry around Cd(1) is an approximate octahedron. The equatorial
positions are occupied by N(1), O(2), N(3), and Cl(2) with the sum of the angles
Cl(2)–Cd(1)–N(1), O(2)–Cd(1)–N(1), Cl(2)–Cd(1)–N(3), and O(2)–Cd(1)–N(3)

Copper and cadmium complexes with quinoline-based benzimidazole
467
Figure 5. The molecular structure of 3 showing the main atom labeling scheme. The hydrogens and crystal
water are omitted for clarity. The suffix A corresponds to symmetry code (ꢁx þ 1, ꢁy þ 1, ꢁz).
being 348.88ꢃ, and the axial positions by Cl(1) and O(1) with the angle of O(1)–Cd(1)–
Cl(1) being 174.06ꢃ and the distances of Cd(1)–O(1) and Cd(1)–Cl(1) 2.500(4) and
˚
˚
2.464(2) A, respectively. The Cd(1) is displaced 0.597 A above the N2OCl coordination
plane and toward the apical Cl(1), due to steric hindrance formed by two chelate rings.
˚
Cd(1)–Cl(2) length of 2.672(2) A is the longest of the six-coordinate bond lengths,
attributed to formation of intermolecular hydrogen bonds by Cl(2) to O(2) and N(2) of
neighboring molecules. The Cd(2) is also six-coordinate, similar to that of Cd(1) with
the coordinated water being replaced by a bridging Cl(4A). The Cl(4) also bridges
another Cd(2A) to form a dinuclear complex [Cd2L2Cl4]. The separation of two
˚
bridging Cd(2)’s in the dinuclear complex is 4.016 A. Because of the bridging
˚
coordination, the Cd(2)–Cl(4A) distance (and Cd(2A)–Cl(4)) reaches 2.929(2) A, the
longest in 3, but still comparable with those in the related complexes [25–27].
The ligand molecules in both Cd(1) and Cd(2) in 3 are almost coplanar, as indicated
by dihedral angles between quinoline and benzimidazole rings of 2.61(2)ꢃ and 5.78(2)ꢃ,
respectively. Each benzimidazolyl in the Cd(1) complex has ꢀ–ꢀ stacking interaction
with another benzimidazolyl from the adjacent Cd(1) unit. The distance between the
˚
stacked planes is 3.299 A. The Cd(1) and Cd(2) complexes are connected by
˚
intermolecular C(29)–H(29) ꢀ ꢀ ꢀ Cl(1) hydrogen bond [C ꢀ ꢀ ꢀ Cl ¼ 3.666(8) A]. A hydrogen
of coordinated water in the Cd(1) unit is hydrogen bonded to two chlorides from two
˚
neighboring Cd(1) complexes [O(2) ꢀ ꢀ ꢀ Cl(2) ¼ 3.230(4) A and O(2) ꢀ ꢀ ꢀ Cl(1) ¼
˚
3.208(4) A]; Cl(2) also has a hydrogen bond interaction with H–N of another Cd(1)
˚
complex [N(2) ꢀ ꢀ ꢀ Cl(2) ¼ 3.178(6) A]. In addition, a hydrogen of benzimidazole in the
Cd(2) complex is hydrogen bonded to Cl(3) of the neighboring Cd(2) complex
˚
[N(5) ꢀ ꢀ ꢀ Cl3 ¼ 3.346(8) A]. These hydrogen bonds and the ꢀ–ꢀ stacking interactions
link 3 to form a 3-D supramolecular structure.
3.5. Electrochemical behaviors of 1–3
Electrochemical behaviors of 1–3 were studied by measuring their cyclic voltammo-
grams in 5 mL of 0.2 mol ꢀ Lꢁ1 BR buffer solution (pH 4.0) containing
1.0 ꢂ 10ꢁ4 mol Lꢁ1 complexes. As shown in figure 6(a), 1 shows a pair of redox peaks
with a cathodic peak potential (Epc) at 0.124 V and an anodic peak potential (Epa) at
0.325 V. The formal potential (E1/2 ¼ 1/2(Epa þ Epc)) and the peak-to-peak potential

468
Y.-H. Wen et al.
Figure 6. Cyclic voltammograms of (a) 1, (b) 2, and (c) 3 in 5 mL 0.2 mol Lꢁ1 BR buffer (pH 4.0). Complex
concentration: 1.0 ꢂ 10ꢁ4 mol Lꢁ1. Scan rate: 100 mV sꢁ1
.

Copper and cadmium complexes with quinoline-based benzimidazole
469
0.25
0.20
0.15
0.10
0.05
0.00
0.6
0.5
0.4
0.3
0.2
0
50
100
150
200
250
300
Temperature (°C)
Figure 7. ꢊM vs. T (g) and ꢊMT vs. T (D) plots of 2.
separation (DEp) were obtained as 0.225 V and 0.201 V, respectively, indicating that the
electrochemical behavior of 1 is quasi-reversible corresponding to Cu(II) þ e $ Cu(I)
[28–30]. Similarly, 2 shows a quasi-reversible one-electron redox at E1/2 ¼ 0.257 V
corresponding to the electrode process Cu(II) þ e $ Cu(I), with Epc at 0.147 V and Epa
at 0.367 V (figure 6b); 3 shows a quasi-reversible two-electron redox process at
E1/2 ¼ ꢁ0.123 V corresponding to Cd(II) þ 2e $ Cd(0), with Epc ¼ ꢁ0.279 V,
Epa ¼ 0.034 V and ipc/ipa ¼ 4.028 (figure 6c) [31, 32].
3.6. Magnetic property of 2
Temperature dependence of the magnetic susceptibility of 2 was investigated in the
temperature range 4–300 K at 2 KOe (figure 7). The ꢊMT versus T plot exhibits a value
of 0.43 emu K Oeꢁ1 molꢁ1 at 300 K and continuously increases on cooling to a value of
0.61 emu K Oeꢁ1 molꢁ1 at 24 K. This behavior of the ꢊMT curve shows ferromagnetic
interactions in 2. However, the curve drops abruptly below 14 K, indicating that an
antiferromagnetic interaction exists in 2 at lower temperatures. The effective magnetic
moment (1.85 ꢆB per Cu) at 300 K is in good agreement with the theoretical value
(1.73 ꢆB) for an uncoupled copper ion, calculated from ꢆeff ¼ 2.828(ꢊMT)1/2. The Weiss
constant, determined in the temperature range 4–300 K, is 8.49 K, suggesting a
predominantly ferromagnetic interaction between the copper centers. According to the
2ꢁ
˚
structural data, the Cu ꢀ ꢀ ꢀ Cu distance in the 1-D chains (6.7177 A) bridged by the SO4
can contribute to the ferromagnetic interaction.

470
Y.-H. Wen et al.
5000
4000
3000
2000
1000
0
1000
800
600
400
200
0
L (Solution)
4 (Solution)
4 (Solid)
300
400
500
600
Wavelength (nm)
Figure 8. Fluorescence spectra of L (red) and 3 (black) in DMSO–water solution, and 3 (blue) in solid state
.
at room temperature. Compound concentration in solution: L, 4.0 ꢂ 10ꢁ3 mol Lꢁ1 and 3, 1.0 ꢂ 10ꢁ3 mol Lꢁ1
3.7. Fluorescent properties
Emission spectra of L and 3 at room temperature are shown in figure 8. In
DMSO–water, free L displays an intense fluorescence emission maximum at 390.2 nm
when excited at 340 nm, assigned to the intraligand (ꢀ–ꢀ*) fluorescent emission. In the
same conditions, 3 exhibits more intense fluorescence with an emission maximum at
417.2 nm upon excitation at 350 nm, red-shifted 27 nm. The enhancement of fluores-
cence in 3 with d10 configuration may be attributed to the chelating coordination of the
ligand to the cadmium [33]. The coordination increases the rigidity of the ligand, as
indicated in X-ray diffraction analysis, and thus reduces the loss of energy through a
radiationless pathway. The significant red shift of the emission in 3 is attributed to
ligand-to-metal charge transfer, which has been found in similar Cd coordination
compounds [34–36]. The fluorescence of 3 in the solid state at room temperature was
also studied, as depicted in figure 8. The solid complex 3 exhibits a purple/blue narrow
emission band (bandwidth at half-height 10 nm) with maximum at 424 nm when excited
at 380 nm, suggesting 3 can be used as an optical material.
4. Conclusion
A new tridentate ligand 2-((quinolin-8-yloxy)methyl)benzimidazole and its three
coordination compounds have been prepared and structurally characterized. The
formation of different complexes depends both on the counteranions and on the metal
cations. In the complexes, L adopts the same coordination and essentially planar
conformation. The electrochemical properties of the complexes show potential for

Copper and cadmium complexes with quinoline-based benzimidazole
471
further applications in electrochemical sensors or electroanalysis. The magnetic and
fluorescent properties suggest the compounds could have potential as ferromagnetic or
fluorescent materials. In view of the flexibility, rigidity, and large planar configuration
with ꢀ-conjugated system of 2-((quinolin-8-yloxy)methyl)benzimidazole, it is possible to
prepare novel complexes with interesting chemical and physical properties.
Supplementary material
Crystallographic data for the structural analysis of the compounds has been deposited
with the Cambridge Crystallographic Data Center (CCDC). CCDC reference numbers
776437–776439 contain the supplementary crystallographic data for this article. These
data can be obtained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
This work was supported by the National Natural Science Foundation of China
(no. 20971076), the Outstanding Adult-Young Scientific Research Encouraging
Foundation of Shandong Province, China (no. 2008BS09017).
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