Syntheses, crystal structures, and luminescent properties of three metal coordination polymers based on adipic acid and 2-(pyridine-3-yl)-(1 H)-benzimidazole

Article abstract of DOI:10.1080/00958972.2015.1084418

Three new metal coordination polymers constructed from adipic acid and 2-(pyridin-3-yl)-(1H)-benzimidazole ligands, [M(ADP)(3PBI)2(H2O)2]·2H2O (M = Ni and Co for 1 and 2, respectively) and [Cd(ADP)(3PBI)(H2O)] (3) [ADP = adipic acid dianion; 3PBI = 2-(pyridin-3-yl)-(1H)-benzimidazole], have been synthesized by hydrothermal reactions and were characterized by X-ray single-crystal diffraction, elemental analyses, IR, powder X-ray diffraction, and thermogravimetry. Complexes 1 and 2 are isostructural. Both form a 1-D linear chain structure, which is further assembled into a 3-D supramolecular framework by ππ stacking and hydrogen bonding interactions. Complex 3 possesses a binuclear unit and displays a 2-D layer which is further extended to a 3-D supramolecular architecture via hydrogen bonding and other weak packing interactions. The luminescent properties of 3 were investigated in the solid state at room temperature.

Full text of DOI:10.1080/00958972.2015.1084418

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Syntheses, crystal structures, and luminescent
properties of three metal coordination polymers
based on adipic acid and 2-(pyridine-3-yl)-(1H)-
benzimidazole
Cui-Cui Wang, Jin-Hua Wang, Gui-Mei Tang, Yong-Tao Wang, Yue-Zhi Cui &
Seik Weng Ng
To cite this article: Cui-Cui Wang, Jin-Hua Wang, Gui-Mei Tang, Yong-Tao Wang, Yue-Zhi Cui &
Seik Weng Ng (2015): Syntheses, crystal structures, and luminescent properties of three metal
coordination polymers based on adipic acid and 2-(pyridine-3-yl)-(1H)-benzimidazole, Journal
of Coordination Chemistry, DOI: 10.1080/00958972.2015.1084418
To link to this article: http://dx.doi.org/10.1080/00958972.2015.1084418
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Date: 22 September 2015, At: 05:19

Journal of Coordination Chemistry, 2015
http://dx.doi.org/10.1080/00958972.2015.1084418
Syntheses, crystal structures, and luminescent properties of
three metal coordination polymers based on adipic acid and
2-(pyridine-3-yl)-(1H)-benzimidazole
CUI-CUI WANG†, JIN-HUA WANG†, GUI-MEI TANG*†, YONG-TAO WANG*†
YUE-ZHI CUI† and SEIK WENG NG‡
†Shandong Provincial Key Laboratory of Fine Chemicals, Department of Chemical Engineering,
Qilu University of Technology, Jinan, China
‡Department of Chemistry, University of Malaya, Kuala Lumpur, Malaysia
(Received 6 May 2015; accepted 27 July 2015)
Three new metal coordination polymers constructed from adipic acid and 2-(pyridin-3-yl)-(1H)-ben-
zimidazole ligands, [M(ADP)(3PBI)2(H2O)2]·2H2O (M = Ni and Co for 1 and 2, respectively) and
[Cd(ADP)(3PBI)(H2O)] (3) [ADP = adipic acid dianion; 3PBI = 2-(pyridin-3-yl)-(1H)-benzimida-
zole], have been synthesized by hydrothermal reactions and were characterized by X-ray single-crys-
tal diffraction, elemental analyses, IR, powder X-ray diffraction, and thermogravimetry. Complexes
1 and 2 are isostructural. Both form a 1-D linear chain structure, which is further assembled into a
3-D supramolecular framework by π⋯π stacking and hydrogen bonding interactions. Complex 3
possesses a binuclear unit and displays a 2-D layer which is further extended to a 3-D supramolecu-
lar architecture via hydrogen bonding and other weak packing interactions. The luminescent proper-
ties of 3 were investigated in the solid state at room temperature.
Keywords: Hydrothermal reaction; 2-(Pyridin-3-yl)-(1H)-benzimidazole; Adipic anion; Luminescence
1. Introduction
The design and construction of metal coordination polymers (MCPs) have received atten-
tion owing to their potential applications as functional materials for gas storage and separa-
tion [1–7], drug delivery [8, 9], catalysis [10, 11], nonlinear optics [12], magnetic materials
[13, 14], sensing [15, 16], luminescence [17, 18], and ferroelectricity [19, 20]. Metal ions
*Corresponding authors. Email: meiguit@qlu.edu.cn (G.-M. Tang); ceswyt@qlu.edu.cn (Y.-T. Wang)
© 2015 Taylor & Francis

2
C.-C. Wang et al.
and the ligands are crucial for the structural architectures and functionalities of MCPs as the
structures and properties of these complexes are influenced by the coordination geometries
of metal ions, the flexibility, shape, symmetry, and substituent groups of ligands [21].
Auxiliary bis-carboxylate ligands can also influence the structures of MCPs, satisfying
charge balance, mediating the coordination geometries of metal centers [22–27], and
providing diverse coordination modes [28, 29]. Construction of diverse architectures as
potential candidates for functional materials remains a challenge.
Numerous MCPs with aliphatic dicarboxylate ligands and N-heteroaromatic ligands have
been developed. The flexibility and conformational freedom of aliphatic dicarboxylate
ligands gives a variety of interesting structural motifs and π⋯π stacking interactions among
N-heteroaromatic ligands, which play very important roles in the construction of MCPs with
interesting supramolecular architectures [30]. Therefore, the synthesis of low dimensional
structures through self-assembly is still a challenge [31–34].
Recently, we designed and synthesized a functional ligand 3PBI (2-(pyridin-3-yl)-(1H)-
benzimidazole), which is a good choice to construct coordination polymers. 3PBI is one
kind of ligand containing a N-heterocyclic group, and possesses the following specific fea-
tures: (1) It has three N-donors which can take part in coordinating with a metal ion, and act
as donor and acceptor of hydrogen bonds. (2) There exist three types of aromatic rings,
pyridine, phenyl, and imidazole, which can conveniently form π⋯π stacking interactions.
Additionally, auxiliary bis-carboxylate ligands can provide charge balance and mediate the
coordination geometries of metal centers and even can provide versatile coordination modes,
which influence the final structures of MCPs. Combining the benefits of bis-carboxylate
ligands and rigid ligands, we chose 3PBI and adipic acid ligands to produce metal–organic
architectures with different structural motifs. Herein, we report the synthesis, structures, and
luminescence of three new MCPs, [M(ADP)(3PBI)2(H2O)2]·2H2O (M = Ni and Co for 1
and 2, respectively), and [Cd(ADP)(3PBI)(H2O)] (3) [ADP = adipic acid dianion,
3PBI = 2-(pyridin-3-yl)-(1H)-benzimidazole], which have been obtained under hydrothermal
conditions. Additionally, their thermogravimetric analyses (TGA) are also discussed.
2. Experimental
2.1. Materials and measurements
Nicotinic acid was purchased from Tian Jin GuangFu Fine Chemical Research Institute. 1,
2-Phenylene diamine and adipic acid were purchased from Sinopharm Chemical Reagent
Limited Corporation. Sodium hydroxide was purchased from Tian Jin Guang Cheng Chemi-
cal Reagent Limited Corporation. Nickel sulfate, cobalt sulfate, and cadmium sulfate were
obtained from Tian Jin Fu Chen Chemical Reagent Factory, Shang Hai Shi Yi Chemical
Reagent Limited Corporation, and Shang Hai Chemical Reagent Corporation, respectively.
Dimethylformamide (DMF) and polyphosphoric acid (PPA) were purchased from Aladdin
Industrial Corporation. 2-(Pyridin-3-yl)-(1H)-benzimidazole (3PBI) was synthesized accord-
ing to literature procedures [35]. The reagents and solvents employed were used as received.
Elemental analyses were performed on an Elementar vario EL III microanalyser. FT-IR spec-
tra were recorded as KBr pellets from 400 to 4000 cm−1 on a Bruker spectrometer. Powder
X-ray diffraction (PXRD) was recorded on a Bruker D8 Avance diffractometer at 40 kV,
40 mA with a Cu-target tube and a graphite monochromator; 2θ falls in the range of 5–60°.

Adipic acid metal coordination polymers
3
The experimental PXRD patterns are in agreement with the corresponding simulated ones
except for the relative intensity variation because of the preferred orientations of the crystals.
Therefore, the phase purity of the as-synthesized products is substantiated. At room tempera-
ture, solid-state fluorescent studies were conducted on a HITACHI F-4600 system. TGA data
were collected with a TA SDT Q600 analyzer in N2 at a heating rate of 10 °C min−1 from 30
to 700 °C.
2.2. Synthesis of 3PBI (2-(pyridin-3-yl)-(1H)-benzimidazole)
To a mixture of solid nicotinic acid (1.354 g, 0.011 mol) and 1,2-phenylene diamine
(1.081 g, 0.010 mol), which was ground and mixed adequately, polyphosphoric acid
(10 mL) was added. The reaction mixture was intermittently heated under microwave
irradiation. Subsequently, two blocks of ice were added. The reaction mixture was cooled
to room temperature and then poured into water (30 mL). The pH of the reaction mixture
was adjusted to 7 by adding 10% NaOH solution. The solid formed was collected and crys-
tallized from pure water to give yellow needle-like crystals. Yield (76.7%, 1.496 g). M.p.
263–269 °C. Microanalyses of 3PBI are in accord with that reported previously [36–38].
2.3. Synthesis of [Ni(ADP)(3PBI)2(H2O)2]·2H2O (1)
A reaction mixture of NiSO4·6H2O (0.0260 g, 0.1 mmol), 3PBI (0.0195 g, 0.1 mmol),
NaOH (0.0072 g, 0.18 mmol), ADP (0.0146 g, 0.1 mmol), and water (6 mL) was added to
a 15-mL Teflon reactor and heated under autogenous pressure at 160 °C for 3 days. The
reaction mixture was cooled to room temperature at a rate of 5 °C h−1. Green pellet crystals
of 1 suitable for X-ray diffraction analysis were obtained (0.032 g, yield: 48.01% based on
NiSO4). Elemental analysis Calcd (%) for C30H34NiN6O8 (665.34): C, 54.16; H, 5.15; N,
12.63; found: C, 54.40; H, 5.17; N, 12.57; IR (KBr, cm−1): 3359(w), 3203(w), 2926(w),
2220(br), 1552(s), 1448(m), 1404(s), 1313(s), 1286(m), 1286(m), 1226(m), 1195(m), 1128
(m), 1055(w), 1028(w), 1001(w), 962(m), 735(s), 690(m), 432(m), 408(w).
2.4. Synthesis of [Co(ADP)(3PBI)2(H2O)2]·2H2O (2)
A reaction mixture of CoSO4·6H2O (0.0280 g, 0.1 mmol), 3PBI (0.0195 g, 0.1 mmol),
NaOH (0.0072 g, 0.18 mmol), ADP (0.0146 g, 0.1 mmol), water (6 mL), and DMF (3 mL)
was added to a 15-mL Teflon reactor and heated under autogenous pressure at 160 °C for
3 days. The reaction mixture was cooled to room temperature at a rate of 5 °C h−1. Red pel-
let crystals of 2 suitable for single X-ray diffraction analysis were obtained (0.008 g, yield:
12.02% based on CoSO4). Elemental analysis Calcd (%) for C30H34CoN6O8 (665.56): C,
54.14; H, 5.15; N, 12.63; found: C, 55.54; H, 5.10; N, 12.68; IR (KBr, cm−1): 3020(w),
2862(w), 2790(w), 2502(w), 1593(s), 1460(w), 1439(w), 1344(m), 1028(m), 892(w), 802
(s), 739(w), 407(w).
2.5. Synthesis of [Cd(ADP)(3PBI)(H2O)] (3)
CdSO4·3/8 H2O (0.026 g, 0.1 mmol), 3PBI (0.0195 g, 0.1 mmol), NaOH (0.0072 g,
0.18 mmol), adipic acid (0.0146 g, 0.1 mmol), and water (6 mL) were added to a 15-mL
Teflon reactor and heated under autogenous pressure at 160 °C for 3 days. The reaction

4
C.-C. Wang et al.
mixture was cooled to room temperature at a rate of 5 °C h−1. Yellow pellet crystals of 3
suitable for X-ray diffraction analysis were obtained (0.0123 g, yield: 27% based on
CdSO4). Elemental analysis Calcd (%) for C18H15Cd N3O5 (465.73): C, 46.38; H, 3.22; N,
9.02; found: C, 46.19; H, 3.24; N, 9.05. IR (KBr, cm−1): 2943(w), 1557(s), 1419(s), 1329
(m), 1278(m), 1197(m), 1130(w), 1049(m), 962(m), 930(m), 816(m), 740(s), 700(m), 637
(m), 519(w), 428(m).
2.6. Single-crystal structure determination
Single-crystal structure determinations of 3PBI and three complexes were measured by an
Agilent Technologies SuperNova Dual diffractometer equipped with
a graphite
monochromator and Mo Kα radiation (λ = 0.71073 Å). The lattice parameters were obtained
by least-squares refinement of the diffraction data. All the measured independent reflections
were used in the structural analysis, and semi-empirical absorption corrections were applied
using the CrysAlis PRO program [39]. SAINT was used for integration of the diffraction
profiles [40]. The structure was solved by direct methods using the SHELXS program of
the SHELXTL package and refined with SHELXL [41, 42]. All non-hydrogen atoms were
located in successive difference Fourier syntheses. The final refinement was performed by
full-matrix least-squares methods with anisotropic thermal parameters for all the non-hydro-
gen atoms based on F2. Except for hydrogen bonded to oxygen, hydrogens were first found
in difference electron density maps, and then placed in calculated sites and included in the
final refinement in the riding model approximation with displacement parameters derived
from the parent atoms to which they were bonded. Special computations for the crystal
Table 1. Crystal data and structure refinement parameters for 3PBI and 1–3.
Compound reference
3PBI
1
2
3
Chemical formula
Formula mass
Crystal system
a (Å)
b (Å)
c (Å)
α (°)
β (°)
C
12H9N3
C30H34N6NiO8
665.34
Triclinic
8.8181(4)
9.7023(8)
9.7404(9)
61.154(9)
86.030(5)
88.029(5)
728.19(10)
100(2)
C30H34CoN6O8
665.56
C18H15CdN3O5
465.73
Monoclinic
10.3656(6)
22.8865(19)
7.7754(4)
90.00
94.931(5)
90.00
1837.7(2)
100(2)
195.22
Monoclinic
10.1952(6)
11.4311(6)
17.2491(9)
90.00
103.490(6)
90.00
1954.79(18)
100(2)
Triclinic
8.8520(4)
9.7334(6)
9.7482(5)
61.221(6)
87.843(4)
85.846(4)
734.23(7)
100(2)
γ (°)
Unit cell volume (Å3)
Temperature (K)
Space group
P21/n
P-1
P-1
P21/c
No. of formula units per unit cell, Z
Radiation type
8
1
1
4
MoKα
0.083
9908
4508
0.0275
0.0565
0.1383
0.0706
0.1495
1.026
MoKα
0.730
6219
3358
0.0312
0.0485
0.1096
0.0540
0.1131
MoKα
0.647
13,347
3395
0.0359
0.0304
0.0687
0.0363
MoKα
1.223
8973
4222
0.0512
0.0538
0.1150
0.0849
0.1349
1.052
Absorption coefficient μ (mm−1
No. of reflections measured
No. of independent reflections
Rint
)
Final R1 values [I > 2σ(I)]a
Final wR(F2) values [I > 2σ(I)]
Final R1 values (all data)
Final wR(F2) values (all data)b
Goodness of fit on F2
0.0738
1.027
1.178
CCDC number
1,061,857
994,668
994,669
994,670
aR1 = ∑||Fo| − |Fc||/∑|Fo|.
bwR2 = [∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]]1/2
.

Adipic acid metal coordination polymers
5
structure discussions were carried out with PLATON for Windows [43]. A summary of the
crystallographic data and structure refinements is listed in table 1. Selected bond lengths
and angles are given in table 2. Corresponding hydrogen bonding data for 3PBI and 1–3
are listed in table 3.
3. Results and discussion
3.1. Description of the crystal structure
3.1.1. Structure description of ligand 3PBI. Single-crystal X-ray analysis for 3PBI
reveals that it has a mononuclear structure which crystallizes in the form of space group
P21/n. There are two 3PBI molecules in the asymmetric unit [figure 1(a)]. As shown in
figure 1(b), a pair of 3PBI molecules, each using the carbons from pyridine groups and
nitrogens from benzimidazole, forms hydrogen bonds (C(5)–H(5)⋯N(5), 3.456(2) Å) (table
3) in the head–tail pattern [44], through which a dimer structure is generated. Consequently,
1-D hydrogen-bonded chains can be observed along the b axis via another weak hydrogen
bond (C(20)–H(20)⋯N(3)c, 3.468(2) Å, cx, −1 + y, z) [figure 1(b) and table 3].
Table 2. Selected bond lengths (Å) and angles (°) for 1–3.
1
Ni(1)–O(1)
Ni(1)–N(1)
2.0614(18)
2.100(3)
87.83(9)
180.00
89.79(9)
86.24(11)
180.00
Ni(1)–O(1W)
2.088(2)
O(1)–Ni(1)–O(1W)
O(1)–Ni(1)–O(1)a
O(1)–Ni(1)–N(1)a
O(1W)–Ni(1)–N(1)a
N(1)–Ni(1)–N(1)a
2
O(1)–Ni(1)–N(1)
O(1)–Ni(1)–O(1W)a
O(1W)–Ni(1)–N(1)
O(1W)–Ni(1)–O(1W)a
O(1)a–Ni(1)–N(1)a
90.21(9)
92.17(9)
93.76(11)
180.00
90.22(9)
Co(1)–O(1)
Co(1)–N(1)
2.0787(13)
2.1491(13)
91.46(5)
93.80(5)
88.54(5)
89.63(5)
Co(1)–O(1W)
2.1094(11)
O(1)–Co(1)–O(1W)
O(1W)–Co(1)–N(1)
O(1W)–Co(1)–O(1)b
N(1)–Co(1)–O(1)b
3
O(1)–Co(1)–O(1)b
O(1W)–Co(1)–N(1)b
O(1)–Co(1)–N(1)
N(1)–Co(1)–N(1)b
180.00
86.20(5)
90.37(5)
180.00
Cd(1)–O(1)
2.377(4)
2.355(4)
2.339(4)
Cd(1)–O(1W)
Cd(1)–N(1)
2.270(4)
2.350(4)
2.465(4)
Cd(1)–O(2)
Cd(1)–O(3)c
Cd(1)–O(4)c
O(1)–Cd(1)–O(1W)
O(1)–Cd(1)–N(1)
O(1)–Cd(1)–O(3)c
O(1W)–Cd(1)–O(2)
O(1W)–Cd(1)–O(3)c
O(1W)–Cd(1)–O(4)c
O(2)–Cd(1)–O(3)c
O(2)–Cd(1)–O(4)d
N(1)–Cd(1)–O(3)c
O(3)c–Cd(1)–O(4)c
95.04(14)
88.13(15)
135.12(13)
106.16(14)
81.10(14)
94.11(13)
82.05(14)
82.97(13)
135.41(15)
54.62(11)
O(1)–Cd(1)–O(2)
O(1)–Cd(1)–O(4)d
O(1)–Cd(1)–O(4)c
O(1W)–Cd(1)–N(1)
O(2)–Cd(1)–N(1)
O(1W)–Cd(1)–O(4)d
O(2)–Cd(1)–O(4)c
N(1)–Cd(1)–O(4)d
N(1)–Cd(1)–O(4)c
O(3)c–Cd(1)–O(4)d
55.93(14)
90.71(13)
167.76(12)
85.44(14)
142.50(15)
170.83(13)
128.57(12)
87.62(12)
84.51(13)
99.81(12)
Symmetry codes:
a1 − x, 1 − y, 1 − z.
b1 − x, 1 − y, 1 − z.
c1 − x, 1/2 + y, 1/2 − z.
dx, 1/2 − y, −1/2 + z.

6
C.-C. Wang et al.
Table 3. Hydrogen bond geometries in the crystal structure of 3PBI and 1–3, respectively.
Compound
D–H⋯Aa
H⋯A (Å)
D⋯A (Å)
D–H⋯A (°)
3PBI
N(2)–H(2)⋯N(5)
C(1)–H(1)⋯N(4)a
N(6)–H(6)⋯N(1)b
C(5)–H(5)⋯N(5)
C(20)–H(20)⋯N(3)c
1.993(12)
2.01(2)
2.873(2)
3.478(3)
2.836(2)
3.456(2)
3.468(2)
176(2)
154(2)
1
N(2)–H(2)⋯O(2)d
2.01(2)
1.89(5)
1.90(4)
1.97(2)
2.01(4)
2.847(4)
2.726(4)
2.682(4)
2.801(3)
2.853(5)
3.392(4)
3.496(5)
160(3)
173(5)
155(3)
177(5)
174(2)
O(1W)–H(11)⋯O(2W)
O(1W)–H(12)⋯O(2)e
O(2W)–H(21)⋯O(2)f
O(2W)–H(22)⋯N(3)
C(8)–H(8)⋯O(2W)
C(14)–H(14)⋯O(2W)g
2
3
N(2)–H(2)⋯O(2)h
2.010(12)
1.89(2)
1.88(2)
2.024(16)
1.959(13)
2.8549(17)
2.6964(19)
2.7222(19)
2.8605(18)
2.7976(16)
3.402(2)
161.4(16)
158.8(18)
178(3)
173(3)
175.8(16)
O(1W)–H(11)⋯O(2)
O(1W)–H(12)⋯O(2W)
O(2W)–H(21)⋯N(3)
O(2W)–H(22)⋯O(2)i
C(8)–H(8)⋯O(2W)
N(2)–H(2)⋯O(2)j
1.97(2)
1.92(4)
1.96(4)
2.820(6)
2.707(5)
2.793(6)
3.206(7)
3.107(6)
162(5)
157(6)
171(6)
O(1W)–H(11)⋯O(3)k
O(1W)–H(12)⋯N(3)l
C(7)–H(7)⋯O(1)
C(11)–H(11A)⋯O(4)m
Symmetry codes:
a1 + x, y, z.
b1 − x,1 − y, 1 − z.
cx, −1 + y, z.
d1 − x, −y, 1 − z.
e1 − x, 1 − y, 1 − z.
f1 + x, y, z.
g2 − x, 1 − y, −z.
hx, y, −1 + z.
i2 − x, 1 − y, 1 − z.
j1 − x, 1 − y, 1 − z.
kx, 1/2 − y, −1/2 + z.
l2 − x, 1 − y, 1 − z.
m1 − x, 1/2 + y, 1/2 − z.
Additionally, each 3PBI using a carbon and the nitrogen from pyridine forms another kind
a
of hydrogen bond (C(1)–H(1)⋯N(4)a, 3.478(3) Å, 1 + x, y, z). A series of chains along the
b axis lie parallel to each other and are connected by this kind of hydrogen bond, resulting
in a wave-like 2-D hydrogen-bonded network along the crystallographic ab plane [figure
a
1(c) and table 3]. Notably, there exist three weak π⋯π (Cg(1)⋯Cg(2)a, 3.505(1) Å, 1 − x,
b
2 − y, 1 − z; Cg(5)⋯Cg(5)b, 3.6962(11) Å, 1 − x, 1 − y, 1−z) packing interactions between
two different benzimidazole groups (Cg(1), Cg(2)) and two identical pyridine groups (Cg
(5)). In addition, there exist two other types of hydrogen bonds (N(2)–H(2)⋯N(5) and N
(6)–H(6)⋯N(1)b distances of 2.873(2) and 2.836(2) Å, respectively, b1 − x, 1 − y, 1 − z)
(table 3). The former is constructed through N(2) and N(5) from two different benzimida-
zole groups; the latter is found through N(6) and N(1) from benzimidazole and pyridine
groups, respectively. These supramolecular interactions extend the 2-D layers to a 3-D
supramolecule [figure 1(d)].

Adipic acid metal coordination polymers
7
Figure 1. (a) A perspective view of 3PBI. (b) A 1-D chain through hydrogen bonds along the b axis. (c) A 2-D
surpramolecular network formed by hydrogen bonding interactions in 3PBI. (d) The packing diagram of 3PBI.

8
C.-C. Wang et al.
3.1.2. Structure description of 1 and 2. Single-crystal X-ray analysis reveals that 1 and 2
are isostructural. They are both 1-D polymers and crystallize in the triclinic space group
P-1. For convenience, the structure of 1 is discussed herein. As shown in figure 2(a), the
asymmetric unit is composed of half of a Ni(II) ion, one 3PBI, half of an ADP ligand, one
coordinated water, and one free water. The central Ni ion is six-coordinate to two nitrogens
from two 3PBI ligands, two oxygens from two ADP ligands, and two water molecules.
The coordination geometry can be described in terms of a slightly distorted octahedral con-
figuration. The Ni–O bond distances in 1 range from 2.061(2) to 2.088(2) Å and the Ni–N
bond length is 2.100(3) Å (table 2), which is in agreement with those published previously
[45]. The bond lengths of Co–O in 2 are 2.0787(13)–2.1094(11) Å, in accord with those
published previously [45]. Interestingly, the average bond length of Co–O is 2.086 Å and
the bond length of Co–N is 2.1491(13) Å, which are slightly longer than the common
Co–O and Co–N distances of 1.94 and 1.96 Å, respectively [45]. The bond angles around
the Co are 80.00(11)–180.00°. Thus, each ADP is a linear connector, which links two
adjacent metal ions. As a result, a 1-D chain is observed [figure 2(b)].
Supramolecular structures mainly depend on three kinds of interactions, coordination
bonds, strong hydrogen bonds, and packing interactions. Intermolecular hydrogen bonds are
formed between 3PBI and ADP ligands. These bond lengths and angles (N–H⋯O) are
2.847(4) Å and 160(3)° for 1, and 2.855(2) Å and 161.4(16)° for 2, through which 1-D
polymeric chains are extended to a 2-D supramolecular layer [figure 2(c)]. We also found
three kinds of O–H⋯O hydrogen bonds and two kinds of C–H⋯O interactions in 1 and 2
[figure 2(d) and table 3]: (a) There exist O–H⋯O intermolecular hydrogen bonds between
coordinated water and free water. These bond lengths and angles are 2.726(4) Å and 173
(5)° for 1, and 2.722(19) Å and 178(3)° for 2. (b) O–H⋯O intermolecular hydrogen bonds
form between oxygens from the coordinated water and oxygens from ADP. These bond
lengths and angles are 2.682(4) Å and 155(3)° for 1, and 2.696(2) Å and 158.8(18)° for 2.
(c) O–H⋯O intermolecular hydrogen bonding occurs between free water molecules and
ADP ligands. These bond lengths and angles are 2.801(3) Å and 177(5)° for 1, and 2.7976
(16) Å and 175.8(16)° for 2. (d) Another type of hydrogen bond occurs between free waters
and 3PBI ligands (O(2W)–H(22)⋯N(3), 2.853(5) Å; C(8)–H(8)⋯O(2W), 3.392(4) Å; C
g
(14)–H(14)⋯O(2W)g, 3.496(5) Å, x, 1/2 − y, −1/2 + z) for 1 and (O(2W)–H(21)⋯N(3),
2.8605(18) Å; C(8)–H(8)⋯O(2W), 3.402(2) Å for 2) (table 3).
Apart from these hydrogen bonding interactions, there exist two kinds of weak π⋯π
stacking interactions between aromatic rings. One occurs between the imidazole groups and
phenyl rings (3.5775 and 3.6560 Å for 1 and 2, respectively) and another between two
phenyl groups (3.6515 and 3.5822 Å for 1 and 2, respectively). These supramolecular
interactions extend the 2-D layers to a 3-D supramolecular architecture, which can support
the stability of the stacked arrangement [figure 2(d)].
3.1.3. Structure description of 3. The results of the X-ray crystallographic analysis reveal
that 3 is a binuclear structure, and crystallizes in the space group P21/c and displays a 2-D
structure of the binuclear units. As shown in figure 3(a), the asymmetric unit contains one
cadmium ion, one 3PBI, one ADP, and one coordinated water. Cd1 is seven-coordinate in
a slightly distorted pentagonal pyramidal geometry. The basal plane consists of one nitrogen
from 3PBI and four oxygens from three different ADP ligands. The axial positions are
occupied by water and the carboxylate from one ADP. The Cd–O bond distances are 2.270
(4)–2.465 Å and the bond length of Cd–N is 2.350(4) Å (table 2), normal values [45]. The

Adipic acid metal coordination polymers
9
Figure 2. (a) A perspective view of the coordination geometry of Ni(II) in 1 (Co(II) center in 2). (b) A 1-D chain
along the c axis in 1. (c) A 2-D surpramolecular network formed by hydrogen bond interactions in 1. (d) The pack-
ing diagram of 1.

10
C.-C. Wang et al.
Figure 3. (a) A perspective view of the coordination geometry of the Cd center in 3 and the binuclear structure in 3.
(b) A 2-D layer along the crystallographic bc plane. (c) The packing diagram of 3. (d) The topology structure of 3.

Adipic acid metal coordination polymers
11
bond angles of O–Cd–O vary from 54.6(1)° to 170.8(1)° and the bond angles of O–Cd–N
are 84.5(1)–142.5(2)°. Interestingly, there are two kinds of adipic acid dianion ligands, one
is bidentate and the other monodentate. As a result, a binuclear Cd structure is formed
[figure 3(a)]. These binuclear units are further extended to a 2-D layer through ADP ligands
[figure 3(b)].
The 3-D supramolecular structures mainly originate from hydrogen bonding and packing
interactions. Four kinds of hydrogen bonds are observed [figure 3(c) and table 3]: (a) An
h
intermolecular hydrogen bond O–H⋯O (O(1W)–H(11)⋯O(3)h 2.707(5) Å, x, 1/2 − y, −1/
2 + z) (table 3) forms between coordinated water and carboxylate of ADP. (b) The inter-
g
molecular hydrogen bond N–H⋯O (N(2)–H(2)⋯O(2)g 2.820(6) Å, 1 − x, 1 − y, 1−z) is
generated through nitrogen of 3PBI and oxygen of ADP. (c) Hydrogen bonds of O–H⋯N
l
(O(1W)–H(12)⋯N(3)l 2.793(6) Å, 2 − x, 1 − y, 1 − z) occur between coordinated water and
nitrogen of 3PBI. (d) Two intermolecular C–H⋯O hydrogen bonds are generated
between carboxylate groups (C(7)-H(7)⋯O(1), 3.206(7) Å; C(11)–H(11A)⋯O(4)m 3.107(6)
Å, m1 − x, 1/2 + y, 1/2 − z).
In addition to these hydrogen bonds, there exist weak π⋯π stacking interactions between
imidazole rings (3.789(3) Å). Consequently, a 3-D supramolecular architecture is
constructed via these hydrogen bonds and weak π⋯π packing interactions along the c axis
[figure 3(c)].
To investigate the topological structure of 3, Cd(II) ions can be regarded as three
connecting nodes, whereas ADP ligands are linear linkers bridging two adjacent Cd(II)
ions. Thus, the whole network is simplified to the (6,3) topological structure, as found in
some 2-D MCPs [figure 3(d)] [46–48]. The present topological network is a non-uniform
topological structure, different from those documented in the literature [49, 50].
3.2. Luminescent properties
Benzimidazole and d10 MCPs are known to show good luminescent properties and 3 is
composed of benzimidazole groups and cadmium ions, which may display interesting lumi-
nescent properties. Hence, the fluorescence emission spectra of 3 were investigated at room
100
80
60
40
20
0
3
3PBI
390
455
520
585
650
Wavelength (nm)
Figure 4. Fluorescent emission spectra of 3PBI and 3 in the solid state at room temperature.

12
C.-C. Wang et al.
temperature [51, 52]. As shown in figure 4, 3 displays an emission band at 413 nm with
excitation at 283 nm. To compare the nature of the emission bands for 3, we investigated
the luminescence properties of free 3PBI in the solid state at room temperature; two
maxima of emission peaks are located at 417 and 541 nm (λex = 283 nm), respectively. In
comparison with 3PBI, the maximum for 3 is slightly blue-shifted about 5 nm and may be
assigned to intraligand π⋯π transition [53]. Compared with the organic ligands, the increase
in 3 could be a consequence of coordination of the organic ligand to the metal center, which
improves the rigidity of the organic ligands, thereby decreasing the loss of energy through a
radiationless pathway [54]. These observations suggest that 3 can serve as a candidate for
luminescent materials.
3.3. PXRD patterns and TGA
In order to confirm the pure phase of these complexes, their PXRD spectra were examined.
As illustrated in figures S1–S3, the peak positions of the simulated and experimental PXRD
patterns are in accord with each other. The present results show that products are in a pure
phase [55].
To examine the thermal stabilities of 1–3, TGA were carried out [56]. The experiments
were performed on samples consisting of single crystals of 1–3 under a N2 atmosphere with a
heating rate of 10 °C min−1 (figures 5, S4 and S5). The TGA curve for 1 is similar to that for
2. The TGA curves show that the first weight loss occurs from 88 to 145 °C (obsd 11.0%,
Calcd 8.1%) for 1 and 86–143 °C (obsd 10.0%, Calcd 8.1%) for 2, which corresponds to loss
of the free and coordination water. The results indicate that there exist strong hydrogen bonds
among the water molecules. The framework collapses from 273 to 694 °C (obsd 68.0%,
Calcd 79.4%) for 1 and 214–693 °C (obsd 68.0%, Calcd 78.9%) for 2, showing the departure
of organic ligands. The remaining weight is attributed to the final product Ni2O3 (obsd
21.0%, Calcd 12.5%) for 1 and Co2O3 (obsd 22.0%, Calcd 13.0%) for 2. The TGA curve of
3 reveals that first weight loss of the coordination water molecules is observed from 121 to
154 °C (obsd 3.4%, Calcd 3.8%). The second weight loss occurs from 226 to 694 °C (obsd
77.6%, Calcd 69.2%), showing the departure of organic ligands. The final residual can be
assigned to the formation of CdO (obsd 19.0%, Calcd 27.0%) for 3.
100
80
60
40
20
100
200
300
400
500
600
700
Temperature (oC)
Figure 5. TGA curve of 1.

Adipic acid metal coordination polymers
13
4. Conclusion
We obtained three MCPs with different dimensionalities, constructed from transition metal
salts with 3PBI and adipic acid dianion under hydrothermal conditions. There exist a variety
of hydrogen bonding and π⋯π stacking interactions, through which 3-D supramolecular
architectures are constructed. The present work shows that the metal centers and the
coordination modes of the bridging ligand play key roles in the final structures. The present
results confirm the significant potential of constructing low dimensional structures based on
bis-carboxylate and N-heterocyclic ligands, providing examples of syntheses of MCPs.
Design and development of MCPs based on other bis-carboxylate ligands and N-heterocyclic
ones are underway at our laboratory.
Acknowledgment
Prof. Yue-Zhi Cui gratefully thanks the National Natural Science Foundation of China [No.
21276149].
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was financially supported by the Project of Shandong Province Higher Educational Science and Technol-
ogy Program [grant number J09LB03]; Shandong Distinguished Middle-aged Young Scientist Encouragement and
Reward Foundation [grant number BS2011CL034]; and Program for Scientific Research Innovation Team in
Colleges and Universities of Shandong Province.
Supplemental data
Supplemental data for this article can be accessed http://dx.doi.org/10.1080/00958972.2015.1084418.
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