A novel Ni(II) coordination polymer constructed from organic acid and bis(imidazol) ligand: Hydrothermal synthesis, crystal structure, and electrochemical properties

Article abstract of DOI:10.1080/15533174.2012.682688

Anovel coordination polymer, [Ni(BDC)(bix)(H₂O)](H ₂BDC=1,4-benzenedicarboxylic; bix = 1,4-bis(imidazol-1-ylmethyl) benzene), has been synthesized under hydrothermal conditions and structurally characterized by elemental analyses, IR

Full text of DOI:10.1080/15533174.2012.682688

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:24–28, 2013
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.682688
A Novel Ni(II) Coordination Polymer Constructed From
Organic Acid and Bis(imidazol) Ligand: Hydrothermal
Synthesis, Crystal Structure, and Electrochemical Properties
Chengyan Zhang,1,2 Fujun Yin,1 Xingyou Xu,3 Baohua Qian,2 Lin Liu,2
and Xujie Yang1
1Department of Chemical Engineering, Nanjing University of Science and Technology,
Jiangsu, P. R. China
2Department of Chemical Engineering, Huaihai Institute of Technology, Jiangsu, P. R. China
3Huaiyin Institute of Technology, Jiangsu, P. R. China
boxylates, and flexible polycarboxylate ligands.[15–19] On the
A novel coordination polymer, [Ni(BDC)(bix)(H2O)] (H2BDC =
1,4-benzenedicarboxylic; bix 1,4-bis(imidazol-1-ylmethyl)
other hand, imidazole-class ligands have been growing con-
cern by people in the ligand design process.[12,20–24] The lig-
and bix(1,4-bis(imidazole-1-ylmethyl)benzene) was an impor-
tant imidazole ligand and used to construct structures for the fol-
lowing merit: the bis(imidazole) groups can afford two N donors
to bridge metal centers, the spacer –(CH2)- can afford flexible
sites and the rigid phenyl ring spacer reduces the flexibility of
the bix ligand. So the bix ligand possesses the combination rigid-
ness and flexibility. While compared with aforementioned cased,
mixed-ligand coordination polymers with aromatic carboxylates
and bix have been rarely presented.[23,24] Herein, we report the
synthesis, crystal structure, thermal behaviors, and electrochem-
ical properties of a novel polymer [Ni(BDC)(bix)(H2O], which
was constructed from the reaction of Ni(II) with mixed ligands
of polycarboxylates and bix.
=
benzene), has been synthesized under hydrothermal conditions and
structurally characterized by elemental analyses, IR spectroscopy,
and single X-ray diffraction. Ni(II) ion in a distorted octahedral
coordination environment and bix plays a bidentate bridging lig-
and to conform the 2D square grid structure which is expands to
the 3D structure through the hydrogen bonds. The thermal and
electrochemical properties of complex were investigated as well.
Keywords crystal structure, electrochemical properties, Ni(II) co-
ordination polymer, 1, 4-benzenedicarboxylic, 1, 4-
bis(imidazol-1-ylmethyl)benzene
INTRODUCTION
The rational design and synthesis of new discrete or poly-
meric metal-organic coordination architectures have received
intense interest not only owing to their variety of intriguing ar-
chitectures and topologies but also their potential application,
such as catalysis, nonlinear optics, magnetism, and electric con-
ductivity.[1–12] Rational control in the construction of polymeric
network remains a great challenge in crystal engineering.[13,14]
The generation of supermolecule framework rests on various
factors, while the regulation and design of the ligand are the
most important.
EXPERIMENTAL
Material and Methods
All chemicals were of reagent-grade quality obtained from
commercial sources and used without further purification.
IR spectra were recorded on a Nicolet NEXUS 470-FTIR
spectrophotometer (USA) as KBr pellets in the 400–4000 cm−1
region. Elemental analyses (C, H, and N) were carried out on a
FLASH EA1112 elemental analyzer (USA). TG-DSC measure-
ments were performed by heating the sample from 20 to 800◦C
at a rate of 10◦C/min on a NETZSCH STA 409PC differential
thermal analyzer (Germany). Cyclic voltammetry of complex
was investigated on a CHI-660B electrochemistry workstation.
The surface-modified Glassy carbon electrode (GCE) was pre-
pared as follows: 5 mg compound 1 accurately weighed was
dissolved in 2 mL Nafion solution, followed by ultrasound for
15 min, and then the suspension solutions were prepared. Us-
ing a microinjector, 5 μL suspension solutions was packed
to the GCE surface, dried with infrared lamp, washed with
As a kind of versatile ligand, carboxylate ligands have been
widely used in the construction of coordination polymers with
desired structure and properties, for example rigid polycarboxy-
late ligands, such as benzenepolycarboxylates, pyridinepolycar-
Received 15 October 2011; accepted 25 March 2012.
The authors gratefully acknowledge Natural Science Fund of
Jiangsu Province (BK2011399).
Address correspondence to Xingyou Xu, Huaiyin Institute of Tech-
nology Huaiyin 223003, Jiangsu, P. R. China. E-mail: 261643494@
qq.com.
24

A NOVEL NI(II) COORDINATION POLYMER
25
TABLE 1
Crystallographic data for complex 1
Empirical formula
Formula weight
T(K)
C22H20N4NiO5
479.13
298(2)
Wavelength
Crystal system, space
group
0.71073 A
Monoclinic, P2(1)/c
a (Å)
15.5099(17)
b (Å)
6.4975(6)
c (Å)
20.2737(18)
90.00
97.2180(10)
90.00
α (◦)
β (◦)
γ (◦)
V (Å3)
2026.9(3)
Z
4
Dc (mg/m3)
F(000)
1.570
992
Crystal size (mm3)
Reflections collected /
unique
0.44 × 0.40 × 0.30
9830/3554 [R(int) = 0.0318]
FIG. 1. The coordination environments for Ni ions in complex 1.
Max. and min.
transmission
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices
[I >2sigma(I)]
R indices (all data)
0.7531 and 0.6669
Synthesis of complex
A mixture of NiSO4·6H2O (0.25 mmol, 0.1315 g), H2BDC
(0.25 mmol 0.084 g), bix (0.25 mmol, 0.143 g), and NaOH
(0.5 mmol, 0.02 g) and 8 mL deionized water were sealed in
25 mL Teflon-lined bomb and heated at 180◦C for 72 h, then
cooled to room temperature at a rate of 10◦C/h. Suituable green
crystals from 1 were filtered off, washed with water, and dried
in air. Crystals of 1 are stable in the air. Yield: 72.6%. Anal.
Calcd. for C22 H20 N4 O5 Ni (%): C: 55.10, H: 4.17, N: 11.69.
Found (%): C: 54.65, H: 5.04, N: 11.95.
3554/0/362
1.038
R1 = 0.0336, wR2 = 0.0777
R1 = 0.0484, wR2 = 0.0863
water and dried with nitrogen, and then surface-modified work-
ing electrode was obtained.
Syntheses of bix
X-Ray Crystallography
The bis(imidazole) ligands were prepared as previously de-
Crystal data and experimental details for compound 1 are
scribed.[25] A solution containing imidazole (6.8 g, 100 mmol) shown in Table 1. A green single crystal of the title compound
and α,αꢁ-dichloro-p-xylene (1.75 g, 10 mmol) in methanol (0.44 mm × 0.40 mm × 0.30 mm) was selected and mounted on
(100 mL) was heated under reflux for 30 h. Removal of most of a glass fiber. All measurements were made on a Bruker Smart
the solvent at reduced pressure gave a light yellow syrup, which 1000 diffractometer (Germany) with a graphite monochromated
was dissolved in 100 mL of aqueous K2CO3(13.50g). This so- MoKα radiation (λ = 0.71073A). All data were collected at
lution upon standing yielded a crystalline of 1,4-bix, which was 298(2) K using the ω-2θ scan mode and corrected for Lorenz
recrystallized from water. Anal. Calcd. for C14H14N4.2H2O: polarization effects. A total of 9830 reflections in the range
C, 61.3; H, 6.6; N, 20.4. Found: C, 61.2; H, 6.5; N, of 0.97 ≤ θ ≤ 25.50 (h: –10∼10, k: –7∼7, l: -23∼22) and
20.3.
3554 unique ones (Rint = 0.0416) were collected. The empirical
TABLE 2
Selected bond distances (Å) and angle (◦) for complex 1
Ni(1)-O(3)
Ni(1)-O(1)
O(3)-Ni(1)-N(4)
N(4)-Ni(1)-N(2)
N(2)-Ni(1)-O(1)
2.0236(17)
2.0893(17)
88.16(8)
177.74(9)
88.89(7)
Ni(1)-N(4)
Ni(1)-O(5)
O(5)-Ni(1)-O(2)
O(3)-Ni(1)-O(1)
O(1)-Ni(1)-O(5)
2.066(2)
2.0981(18)
163.00(7)
162.43(7)
102.47(7)
Ni(1)-N(2)
Ni(1)-O(2)
O(3)-Ni(1)-N(2)
N(4)-Ni(1)-O(1)
N(4)-Ni(1)-O(5)
2.069(2)
2.2589(18)
91.36(8)
90.90(8)
87.49(8)

26
C. ZHANG ET AL.
FIG. 2. (A) 2D rectangular structure from complex 1 at the b-axis. (B) Hydrogen bonds for complex 1 along the a-axis (bix are omitted for clarity).
absorption corrections by SADABS were carried out (University is six-coordinated in the distorted octahedron environment. For
of Go¨ttingen, Germany).
a six-coordinate Ni(II) atom, the equatorial plane is defined by
The structure was solved by direct methods and expanded three carboxylate oxygen atoms (O1, O2, and O3) from BDC2–
by Fourier technique with SHELX-97 program (University of units and one oxygen atom from water molecule (the mean
Go¨ttingen, Germany).[26] The non-hydrogen atoms were re-
fined with anisotropic thermal parameters. The N3 and C8-
C14 are disorders and the position occupancy is 0.52. The
hydrogen atoms bound to carbon were placed geometrically.
The selected bond distances and angles are presented in
Table 2.
RESULTS AND DISCUSSION
The single-crystal structure shows that compound 1 crystal-
lizes in group P2(1)/c. As shown in Figure 1, the fundamental
unit of complex 1 is composed of a Ni(II) atom, a BDC2– an-
ion, a bix, and a water molecule. The geometry around Ni(II)
TABLE 3
ydrogen bonds for complex 1
D-H
d(D-H) d(H..A) <DHA d(D..A)
0.850 1.972 138.11 2.666
A
O(5)-
O(4)
H(5B)
O(5)-
H(5C)
0.850 2.094 145.89 2.838 O(2) [x, y + 1, z]
FIG. 3. The 3D structure for complex 1 (dotted lines represent the hydrogen
bonds).

A NOVEL NI(II) COORDINATION POLYMER
27
deviation from the plane is 0.1017 Å), and the axial positions
are occupied by two nitrogen atoms from imidazoles of different
bix ligands. The Ni-O distances fall in the range 2.0238–2.2589
Å while the Ni-N2 and Ni-N4 distances are 2.069(2) Å and
2.066(2) Å, respectively (Table 2). The bond angles around
central Ni ion vary from 60.84(6)◦ to 177.74(9)◦ compared with
from 90◦or 180◦ for an ideal octahedral structure.
The BDC2– ligand exhibits two types of coordination modes:
one carboxylate acts as a bidentate bridging ligand to chelate
four-membered ring while the other shows monodentate coordi-
nation. BDC2– acts as a bridging ligand and propagates the chain
in a zigzag manner along 001 direction and make the angle 139◦
(Figure 2). The bix ligand is present in an anti conformation and
bridges the Ni(II) of the adjacent sheets to conform 2D square
grid structure to get two quadrangle channels at 1.08∗0.55 nm2
and 1.08∗0.39 nm2 (Figure 2).
FIG. 5. Cyclic voltammogram of complex 1 at 20 mVs–1 scan rates.
The coordinated water molecule, O(5), acts as hydrogen-
bond donors to O4 and O2 of carboxylic ion, O(5)-H(5). . .O(4)
(2.666Å) and O(5)-H(5)C. . .O(2) (2.838Å; Table 3). The 2D
square grid structure conforms to 3D structure through the hy-
drogen bond (Figure 3)
to the decomposition of organic ligands. Then to 800◦C, there
is NiO left (found 16.13%, calcd. 15.59%).
Electrochemical Properties
The complex electrochemical behaviors were investigated in
a three-electrode system, using a surface-modified glassy carbon
electrode(GCE; ϕ3 mm) working electrode, a Pt wire auxiliary
electrode, and a saturated calomel electrode as the reference
electrode.
IR and Thermal Analysis
The IR analysis of the complex is consistent with their crystal
analysis. The band attributable to H2O occurs at 3384 cm–1. For
the complex, the 1564 cm–1 and 1379 cm–1 are the vas(OCO)
and vs(OCO) stretch vibration, respectively. The undeproto-
nated carboxyl group of free H2BDC at 1680 cm–1 disappear.
The absorption bands at 1513 cm–1 and 1422 cm–1 can be as-
signed to the vibrations of the C N and C C in the imidazole
ring.
The TG curve (Figure 4) shows that there two weight-loss
processes. The one (3.85%) below 281◦C is attributed to the loss
of one coordinated water molecule (calcd. 3.75%). From 396 to
4566◦C there is a sharp weight-loss step that can be attributed
Surface-modified GCE by complex 1 was used to study its
redox properties in the solid state by cyclic voltammetry, and
the result obtained is shown in Figure 5. The electrochemical
behaviors were studied in phosphate buffer solution (pH = 8).
In the potential range of +1.5V to −1.2V with 20 mVs–1 scan
rate, there is a pair of redox peaks corresponding to the redox
couple of Ni(II)/Ni (Epa = −0.241 V and Epc = −0.691 V).
1
The half-wave potentials potential (E = (Epa + Epc)/2) is
2
−0.466 V.The peak-to-peak separation (ꢂE) is 0.450 V and the
ipc/ipa is 9.48, exhibiting a quasireversible electrode process.
The cathode peak is higher than the anode peak which shows
that the Ni(II) is reduced easily and oxidized hardly.
SUPPLEMENTARY MATERIALS
Crystallographic data for the structural analysis has been
deposited with the Cambridge Crystallographic Data Centre,
CCDC No.826989 for compound 1. Copies of this infor-
mation may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +
44–1223–336033; E-mail: deposit@ccdc.cam.ac.uk or www:
http:// www.ccdc.cam.ac.uk).
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FIG. 4. Thermogravimetric curve of complex 1.

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