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G.-Q. Zhong et al. / Polyhedron 111 (2016) 11–15
[Hbpt = 1H-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole], {[Ni2(btca)
(bpym)(H2O)4]ꢀ4H2O}n [37] (bpym = 5,50-bipyrimidine), {[Ni2(btca)
(pyz)(H2O)4]ꢀ2H2O}n [38] (pyz = pyrazine), Ni2(btca)(bpy)3ꢀ3DMF
[39] (DMF = N,N0-dimethylformamide) and so on.
Green block crystals of the title complex were obtained. The crys-
tals were collected by filtration, and dried at room temperature.
The yield of the complex was 34% (based on Ni). Anal. Calc. for
Ni2C34H26O10N8: Ni, 14.24; C, 49.51; H, 3.16; N, 13.59. Found: Ni,
14.15; C, 49.21; H, 3.14; N, 13.51%.
To our knowledge, nickel(II) is an essential ultra trace metal ele-
ment for human nutrition, and it maintains normal physiological
functions [40]. In this paper, 1,2,4,5-benzenetetracarboxylic acid
is chosen as the primary anionic ligand, 1,4-bis(imidazol-1-yl)ben-
zene (1,4-bib) acts as ancillary neutral ligand and nickel chloride
hexahydrate acts as the central ion. We have synthesized a novel
homodinuclear coordination polymer [Ni2(btca)(1,4-bib)2(H2O)2]n
using the hydrothermal method. Herein, we report the composi-
tion and crystal structure of the complex, which has been charac-
terized by elemental analyses, single crystal X-ray diffraction, FT-
IR, TG-DSC and its magnetic property.
2.3. X-ray crystallography
A single crystal of the title complex was studied on a Bruker
Smart Apex II CCD diffractometer with graphite monochromated
Mo Ka radiation (k = 0.71073 Å) and x-2h scans. The data were col-
lected at 298(2) K. A colorless and transparent crystal with dimen-
sions 0.35 ꢂ 0.33 ꢂ 0.24 mm was mounted on a glass fibre. The
structure was solved by direct methods with the SHELXS-97 program
and refined on F2 by full-matrix least-squares using SHELXL-97 [41].
All non-hydrogen atoms were refined anisotropically. Hydrogen
atoms of the organic ligands were placed at calculated positions
and refined using the riding model. All water hydrogen atoms were
found in difference Fourier maps and refined isotropically in the
title complex.
2. Experimental
2.1. Materials and physical measurements
The chemicals 1,2,4,5-benzenetetracarboxylic acid and 1,4-bis
(1H-imidazol-4-yl)benzene were purchased from Jinan Henghua
Sci. & Tec. Company Ltd., while nickel chloride hexahydrate was
purchased from Merck Chemicals (Shanghai) Co., Ltd. All chemicals
purchased were of analytical reagent grade and used without fur-
ther purification.
The carbon, hydrogen and nitrogen contents in the complex were
measured on a Perkin–Elmer 240 elemental analyzer and the nickel
content was determined with a Thermo X-II inductively coupled
plasma mass spectrometer. IR spectra were recorded from potas-
sium bromide pellets in the range 4000–400 cmꢁ1 on a Perkin–
Elmer Spectrum One spectrometer. Thermogravimetric analysis of
the metal complex was performed by a SDT Q600 thermogravimet-
ric analyzer, and the measurements were recorded from ambient
temperature to 600 °C at a heating rate of 10 °C minꢁ1 under an air
flow of 100 mL minꢁ1. The variable temperature magnetic suscepti-
bility measurement of the complex was performed on a Quantum
Design SQUID MPMS XL-7 instrument in the temperature range
2–300 K under a field of 1000 Oe.
3. Results and discussion
3.1. X-ray crystal structure analysis
The single crystal X-ray diffraction analysis revealed that the
title complex crystallizes in the triclinic system with space group
P1. Crystallographic data and structure refinement parameters for
the title complex are given in Table 1 and selected bond distances
and angles are shown in Table S1. Key fragments of the structures
and the atom numbering are shown in Fig. 1. The complex is the
dinuclear species [Ni(1,4-bib)(H2O)(l-C6H2(COO)4)Ni(1,4-bib)
(H2O)]. There are two crystallographically unique nickel(II) cations,
one btca4ꢁ anion ligand, two 1,4-bib neutral ligands and two coor-
dinated water molecules in the asymmetrical structural unit. The
pyromellitate ligands utilize the hydroxyl atoms O2 and O2#1 in
the bridged coordination mode from the carboxylate group to link
the nickel(II) cations, and the nuclear separation between the Ni1
and Ni1#1 atoms is 3.246 Å; this value is slightly larger than
3.079 Å from a dinuclear nickel(II) macrocyclic complex which is
bis-bridged by phenolic oxygen atoms [42]. The two nickel(II)
cations in the title complex show identical coordination environ-
ments, and the Ni1, O2, Ni1#1 and O2#1 atoms are in the same
plane. The crystal packing diagram of the complex is shown in
Fig. S1. Each nickel(II) center is hexacoordinated by two nitrogen
atoms from two 1,4-bib ligands [Ni1–N2 = 2.097(4) Å and
Ni1–N4 = 2.073(4) Å], three carboxyl oxygen atoms from two dif-
ferent btca4ꢁ ligands [Ni1–O3#1 = 2.031(3) Å, Ni1–O2#1 = 2.066
2.2. Synthesis of the complex
A mixture of pyromellitic acid (0.15 mmol, 0.038 g), 1,4-bis(1H-
imidazol-4-yl)benzene (0.30 mmol, 0.063 g), nickel chloride hex-
ahydrate (0.30 mmol, 0.071 g), sodium hydroxide (0.40 mmol,
0.016 g), 2 mL ethanol, and 12 mL water was placed in a 30 mL
Teflon-lined stainless steel vessel, heated at 170 °C for 72 h, fol-
lowed by slow cooling to room temperature at a rate of 5 °C hꢁ1
.
Table 1
Crystal data and structure refinement parameters for the title complex.
Empirical formula
Formula weight (g molꢁ1
T (K)
Wavelength (Å)
Crystal system
Space group
Ni2C34H26O10N8
824.05
293(2)
0.71073
triclinic
Absorption coefficient (mmꢁ1
F(000)
)
1.307
422
)
Crystal size (mm3)
0.35 ꢂ 0.33 ꢂ 0.24
Theta range for data collection (°)
Limiting indices
Reflections collected/unique
2.61–25.02
ꢁ9 6 h 6 7, ꢁ9 6 k 6 11, ꢁ11 6 l 6 11
4427/2712 [R(int) = 0.0692]
P1
a (Å)
b (Å)
c (Å)
8.0805(11)
9.8771(12)
10.0147(14)
96.443(2)
102.682(4)
96.393(2)
767.21(18)
1
Completeness to theta = 25.02
Absorption correction
Maximum and minimum transmission
Refinement method
99.9%
Semi-empirical from equivalents
0.7444 and 0.6576
Full-matrix least-squares on F2
2712/0/244
a
(°)
b (°)
Data/restraints/parameters
c
(°)
Goodness-of-fit (GOF) on F2
1.048
V (Å3)
Final R indices [I > 2
r(I)]
R1 = 0.0588, wR2 = 0.1206
R1 = 0.0806, wR2 = 0.1396
0.614 and ꢁ0.799
Z
R indices (all data)
Dcalc (g cmꢁ3
)
1.784
Largest difference peak and hole (e Åꢁ3
)