Three new d10 coordination polymers based on 2-(2-pyridyl)benzimidazole ligand: Synthesis, structures and properties

Article abstract of DOI:10.1016/j.inoche.2010.07.029

Three coordination polymers containing 2-(2-pyridyl)benzimidazole (PyHBIm) ligand, namely {[Zn₃(PyBIm)₃(PyHBIm)₂(tma) (H₂O)]?H₂O}_n (1), [Zn(PyHBIm)(oba)] _n (2), [Cd(PyHBIm)(oba)]

Full text of DOI:10.1016/j.inoche.2010.07.029

Inorganic Chemistry Communications 13 (2010) 1332–1336
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Three new d10 coordination polymers based on 2-(2-pyridyl)benzimidazole ligand:
Synthesis, structures and properties
⁎
⁎
Cheng-Jun Wang, Ke-Fen Yue , Wei-Hong Zhang, Jun-Cheng Jin, Xiao-Ying Huang, Yao-Yu Wang
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, Shaanxi Key Laboratory of Physico-Inorganic Chemistry,
College of Chemistry & Materials Science, Northwest University, Xi'an 710069, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three coordination polymers containing 2-(2-pyridyl)benzimidazole (PyHBIm) ligand, namely {[Zn3(PyBIm)3
(PyHBIm)2(tma)(H2O)]•H2O}n (1), [Zn(PyHBIm)(oba)]n (2), [Cd(PyHBIm)(oba)]n (3), (tma=trimesate,
oba=4,4′-oxybis-(benzoate)), have been prepared through hydrothermal reaction. Compound 1 exhibits one-
dimensional (1D) helical structure. However, compounds 2 and 3 display 1D meso-helical structure. These 1D
structures are further assembled into three-dimensional (3D) networks through aromatic π–π stacking
interactions and hydrogen bonding interactions. Moreover they all exhibit strong photoluminescence at room
temperature and may be good candidates for potential luminescence materials.
Received 8 June 2010
Accepted 20 July 2010
Available online 29 July 2010
Keywords:
2-(2-pyridyl)benzimidazole
Coordination polymer
Crystal structure
© 2010 Elsevier B.V. All rights reserved.
Photoluminescence
Over the past few decades, much effort has been paid to the study of
metal coordination polymers due to their fascinating structures as well
as potential applications, such as molecular based magnet, catalysis,
luminescence, ion exchange and adsorption [1–6]. So far, large numbers
of coordination polymers with interesting compositions and topologies
have been prepared. Among these, the construction of helical structures
has always been a popular subject because helicity plays a critical role in
biology systems [7,8] and advance materials such as optical devices and
asymmetric catalysis [9–12]. One of the best approaches toward the
helical coordination polymer networks involves the use of one or more
flexible or V-shaped bidentate bridging ligands [13–16] and chelate
end-blocking ligands such as 2,2′-bipyridyl and 1,10-phenanthroline
[17–20]. However, 2-(2-pyridyl)benzimidazole (PyHBIm), as a chelate
ligand, is rarely investigated, which has multiple coordination modes in
forming metal coordination polymers. It can not only be chelate end-
blocking ligand but also can be bridging ligand when it is deprotonated.
As we know, an odd carboxylate anion ligand and divalent metal ions
cannot reach charge balance, which will require the PyHBIm ligand to
deprotonate to make the coordination polymer reach charge balance.
Therefore, trimesate (tma) is used for our synthetic strategy. With these
background in mind, three new one-dimensional metal-organic
coordination polymers, {[Zn3(PyBIm)3(PyHBIm)2(tma)(H2O)]•H2O}n
(1), [Zn(PyHBIm)(oba)]n (2), [Cd(PyHBIm)(oba)]n (3) (oba=4,4′-
oxybis-(benzoate)), have been prepared through hydrothermal reac-
tion. They exhibit two different kinds of helical structures. Compound 1
exhibits 1D helical structure that is further assembled into 3D networks
through aromatic π–π stacking interactions and hydrogen bonding
interactions. When another carboxylate ligand is used in the place of
tma under the same condition, compounds 2 and 3 have been obtained
which display 1D meso-helical structures thatare also further assembled
into 3D networks through aromatic π–π stacking interactions and
hydrogen bonding interactions. Compared with helical structure, meso-
helical structure is more special and coordination polymers with this
kind of structure have been rarely reported [21–24]. In compounds 2
and 3, the PyHBIm ligand is neutral with one kind of coordination mode.
However, it is partly deprotonated with three kinds of coordination
modes in compound 1, which is, to our knowledge, the first example
that three kinds of coordination modes of PyHBIm ligand exist in one
compound. Moreover, compounds 1–3 exhibit strong photolumines-
cence at room temperature and may be good candidates for potential
luminescence materials.
X-ray diffraction analysis reveals that 1 exhibit 1D helical structure
with space group Pī. There are three zinc atoms, one tma ligand, one
coordinated water, one free water, three anionic PyBIm ligands and two
neutral PyHBIm ligands in the asymmetry unit (Fig. 1). The Zn1 atom is
coordinated by two nitrogen atoms of one PyBIm ligand (Zn(1)-N(5)
2.023(6), Zn(1)-N(4) 2.176(6) Å), two nitrogen atoms of one PyHBIm
ligand (Zn(1)-N(1) 2.113(6), Zn(1)-N(3) 2.271(6) Å) and two oxygen
atoms from one tma ligand (Zn(1)-O(1) 2.212(5), Zn(1)-O(2) 2.241
(4) Å), showing a distorted octahedral geometry. The Zn2 atom is
coordinated by four nitrogen atoms from two different PyBIm ligands
(Zn(2)-N(10) 2.043(5), Zn(2)-N(7) 2.043(5), Zn(2)-N(12) 2.156(5), Zn
(2)-N(9) 2.187(5) Å) and two oxygen atoms from one tma ligand (Zn
(2)-O(3) 2.224(4), Zn(2)-O(4) 2.291(4) Å), showing a distorted
octahedral geometry. The structure shows a distorted trigonal bipyra-
midal configuration with five coordinations to the Zn3 atom. And it is
⁎
Corresponding authors. Tel.: +86 29 88303097; fax: +86 29 88302604.
E-mail addresses: ykflyy@nwu.edu.cn (K.-F. Yue), wyaoyu@nwu.edu.cn
(Y.-Y. Wang).
1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2010.07.029

C.-J. Wang et al. / Inorganic Chemistry Communications 13 (2010) 1332–1336
1333
Fig. 1. The coordination environment of the Zn(II) atoms in compound 1.
coordinated by one nitrogen atom from one PyBIm ligand (Zn(3)-N(11)
2.043(5) Å), two nitrogen atoms from one PyHBIm ligand (Zn(3)-N(13)
2.175(5), Zn(3)-N(15) 2.186(6) Å), one oxygen atom from one tma
ligand (Zn(3)-O(5)#1 2.101(4) Å) and one oxygen atom from water (Zn
(3)-O(7) 2.008(4) Å). The selected bond lengths and angles for 1 are
listed in Table S1. The neighboring Zn2 and Zn3 atoms are bridged by
interval PyBIm and tma ligands which form a 1D helical chain running
along b axis (Fig. 2a). The pitch of the helix is 13.53 Å. There are three
kinds of hydrogen bonds between the adjacent chains. The first is
connecting oxygen atoms of coordinated water molecules with
uncoordinated nitrogen atoms (O7-H7WA···N8). The second is
between uncoordinated nitrogen atoms and carboxylate oxygens
(N14-H14A···O3). These two kinds of hydrogen bonds direct the 1D
chain to form a 2D structure (Fig. S1). The third is connecting nitrogen
atoms and carboxylate oxygens (N2-H2A···O2) (Fig. 2b), allowing the
2Dstructuretoform a 2D bilayer structure (Fig. S2). Otherwise, there are
three kinds of coordination modes of PyHBIm ligands in the asymmertry
unit, as illustrated in Scheme 1. Notably, to our knowledge, it has never
been reported that three kinds of coordination modes of PyHBIm ligands
exist in one compound until now. One PyBIm group bridging Zn2 and
Zn3 by the third coordination mode (Scheme 1c), which is an important
factor in formingthe 1Dchain structure. Two PyBIm ligands connect Zn2
and Zn3 in two different chelate coordination modes (Scheme 1a and b)
from the opposite sides of the helix chain, which allow the helixs to pack
into a 2D layer network through strong π–π stacking interactions with
face to face distance of 3.706(2) Å (Fig. 2c). Such grid layers are further
extended into the final 3D supramolecular network via π–π stacking
interactions of PyBIm rings from different layers and hydrogen bonding
interactions (Fig. 2d).
When the oba ligand is used in the place of tma under the same
condition, compounds 2 and 3 have been obtained through hydrothermal
reaction. X-ray diffraction analysis reveals that 2 and 3 are isomorphous,
Fig. 2. The views of helical chain (a), π–π stacking interactions and hydrogen bonding interactions (b), 2D layers along the ab plane (c) and 3D networks (d) in 1.

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C.-J. Wang et al. / Inorganic Chemistry Communications 13 (2010) 1332–1336
Scheme 1. Coordination Modes of 2-(2-pyridyl)benzimidazole (PyHBIm) in Compound 1.
so that only the structure of 2 is described here. Compound 2 contains 1D
meso-helical chain constructed by oba ligands and zinc ions. In 2, the
asymmetric unit consists of one Zn atom, one oba ligand and one PyHBIm
ligand, as shown in Fig. 3. The zinc(II) atom is coordinated by four oxygen
atoms from two oba ligands (Zn(1)-O(1) 2.126(5), Zn(1)-O(2) 2.147(5),
Zn(1)-O(5)#1 2.150(4), Zn(1)-O(4)#1 2.232(5) Å) and two nitrogen
atoms from PyHBIm ligand (Zn(1)-N(1) 2.236(7), Zn(1)-N(2) 2.035(6)
Å), showing a distorted octahedral geometry. The selected bond lengths
and angles for 2 and 3 are listed in Table S1. The neighboring zinc atoms
are bridged by long flexible spacers in a chelate coordination mode to form
a meso-helical chain running along a axis (Fig. 4a). The pitch of the helix is
25.28 Å. The two benzene rings of oba ligand are severely bent which is an
important factor in forming the meso-helical structure. All PyHBIm groups
bristle out from the two sides of the helix which play a critical role in
packing into a higher network through π–π stacking interactions. The
adjacent meso-helical chains are intercalated into two-dimensional (2D)
grid layers parallel to the ab plane (Fig. 4c) through hydrogen bonding
interactions (N3-H3A···O5) and strong aromatic π–π stacking interac-
tions between PyHBIm ligands with face to face distance of 3.669(2) Å
(Fig. 4b). Such grid layers are further extended into the final 3D
supramolecular network via π–π stacking interactions of PyHBIm rings
from different layers (Fig. 4d).
one tma group (calculated: 17.45%). The DSC curve shows a sharp
exothermic peak at near 350 °C. Compounds 2 and 3 are stable up to
near 410 °C and 385 °C respectively, and then start to decompose (Figs.
S4 and S5). Compounds 1–3 exhibit strong photoluminescence in the
solid state at room temperature. The emission spectra are shown in
Fig. 5. Excitation of solid sample of 1 at λ=300 nm produces an intense
luminescence with a peak maximum at 440 nm. Excitation of solid
sample of 2 at λ=260 nm produces an intense luminescence with a
peak maximum at 416 nm. Excitation of solid sample of 3 at λ=280 nm
produces an intense luminescence with a peak maximum at 422 nm.
And the peaks of 2 and 3 are stronger and sharper than that of 1. We
have analyzed the photoluminescence properties of the free PyHBIm
molecule which displays a weak luminescence at ca. 370 nm in the solid
state at room temperature. It has been reported that organic compound
oba does not emit any luminescence in the range of 400–800 nm [17].
These emission bands might be assigned to the emission of metal-to-
ligand charge transfer (MLCT) [25,26].
Three new metal-organic coordination polymers containing 2-(2-
pyridyl)benzimidazole have been successfully synthesized by hydrother-
mal reaction. They exhibit two different kinds of 1D helical structures.
Compound 1 exhibits 1D helical structure. However, compounds 2 and 3
display 1D meso-helical structure. These 1D structures are further
assembled into three-dimensional (3D) networks through aromatic π–π
stacking interactions and hydrogen bonding interactions. In compounds 2
and 3, the PyHBIm ligand is neutral with one kind of coordination mode,
whereas it is partly deprotonated with three kinds of coordination modes
in compound 1, which owing to the change of carboxylate ligands
between them. And, to our knowledge, there is no previous example that
Thermal analyses for compounds 1–3 are performed in the N2
atmosphere between 20 and 1000 °C. The results show that these
complexes have similar stability in the range of 100–500 °C. Compound
1 is stable up to near 320 °C, and then begins to decompose (Fig. S3).
Compound 1 gets weight loss of 20.13% in the temperature range 100–
500 °C which corresponds to the releases of two water molecules and
Fig. 3. The coordination environment of the Zn(II) atom in compound 2.

C.-J. Wang et al. / Inorganic Chemistry Communications 13 (2010) 1332–1336
1335
Fig. 4. The views of meso-helical chain (a), π–π stacking interactions and hydrogen bonding interactions (b), 2D layers along ab plane (c) and 3D networks (d) in 2 and 3.
three kinds of coordination modes of PyHBIm ligand exist in one
compound. In summary, the carboxylates and the deprotonated or
neutral PyHBIm ligands dominate the coordination structures. Mean-
while, the intermolecular π–π stacking interactions and hydrogen
bonding interactions have a significant influence on the supramolecular
structures. Moreover, compounds 1–3 exhibit acceptable thermal stability
and strong photoluminescence at room temperature.
This work was supported by the Natural Scientific Research
Foundation of Shaanxi Provincial Education Office (No. 08JK461),
the Postdoctoral Science Foundation of Northwest University (No.
BK08008) and the State Key Program of National Natural Science of
China (No. 20931005).
Synthesis of {[Zn3(PyBIm)3(PyHBIm)2(tma)(H2O)]•H2O}n (1): A solu-
tion of Zn(OAc)2•2H2O (0.220 g, 1.0 mmol), PyHBIm (0.195 g, 1.0 mmol),
tma (0.042 g, 0.20 mmol), NaOH (0.040 g, 1.0 mmol) and H2O (15 mL)
was stirred under ambient conditions, then sealed in a Teflon-lined steel
autoclave, heated at 160 °C for 5 days, and cooled to room temperature at
a rate of 5 K/h. The resulting product was recovered by filtration, washed
with distilled water and dried in air (70% yield). Anal. Calcd (%) for
14.78. IR (KBr pellet, cm-1): 3423 w, 3054 w, 1607 s, 1559 m, 1445 s,
1421 s, 1364 s, 1150 w, 1049 w, 1008 w, 796 w, 741 s, 643 w.
Synthesis of [Zn(PyHBIm)(oba)]n (2): A solution of Zn(OAc)2•2H2O
(0.220 g, 1.0 mmol), PyHBIm (0.195 g, 1.0 mmol), oba (0.256 g,
1.0 mmol), NaOH (0.04 g, 1.0 mmol) and H2O (15 mL) was stirred
under ambient conditions, then sealed in a Teflon-lined steel autoclave,
heated at 160 °C for 5 days, and cooled to room temperature at a rate of
5 K/h. The resulting product was recovered by filtration, washed with
distilled water and dried in air (75% yield). Anal. Calcd (%) for
C26H16N3O5Zn: C, 60.54; H, 3.13; N, 8.15. Found: C, 60.12; H, 3.05; N,
7.96. IR (KBr pellet, cm−1): 3435 s, 1599 s, 1545 m, 1498w, 1392 s,
1232 m, 1156 w, 1096 w, 928 w, 877 w, 787 w, 744 m, 661 w.
Synthesis of [Cd(PyHBIm)(oba)]n (3): Compound 3 was synthesized
in a procedure analogous tothat of 2 except thatthe Zn(OAc)2•2H2O was
replaced by Cd(OAc)2•2H2O. The resulting product was recovered by
filtration, washed with distilled water and dried in air (75% yield). Anal.
Calcd (%) for C26H16N3O5Cd: C, 55.48; H, 2.87; N, 7.47. Found: C, 55.16;
H, 2.61; N, 7.21. IR (KBr pellet, cm−1): 3415 s, 1596 s, 1546 m, 1497 w,
1395 s, 1230 m, 1158 w, 1096 w, 977 w, 878 w, 776 w, 737 m, 657 w.
Crystal data for 1: {[Zn3(PyBIm)3(PyHBIm)2(tma)(H2O)]•H2O}n,
T=293(2) K, M=1410.33, Triclinic, space group Pī, a=11.930(17) Å,
b=13.534(19) Å, c=21.013(3) Å, α=90.597(2)°, β=100.438(2)°,
γ=112.774(2)°. V=3064.3(8) Å3, Z=2, R1 =0.0624, wR2 =0.1280,
GOF=0.998.
C69H46N15O8Zn3: C, 58.89; H, 3.15; N, 14.93. Found: C, 58.76; H, 3.05; N,
Crystal data for 2: [Zn(PyHBIm)(oba)]n, T=293(2) K, M=516.8,
Monoclinic, space group P21/n, a=7.4391(12) Å, b=18.537(3) Å,
c=16.235(3) Å, α=90°, β=99.742(2)°, γ=90°. V=2206.6(6) Å3
Z=4, R1 =0.0738, wR2 =0.1711, GOF=1.037.
,
Crystal data for 3: [Cd(PyHBIm)(oba)]n, T=293(2) K, M=563.8,
Monoclinic, space group P21/n, a=7.4964(11) Å, b=18.366(3) Å,
c=16.569(2) Å, α=90°, β=97.785(2)°, γ=90°. V=2260.1(6) Å3,
Z=4, R1 =0.0672, wR2 =0.1886, GOF=1.022.
Suitable single crystals of 1–3 were carefully selected under an
optical microscope and glued to thin glass fibers. The diffraction data
were collected on a Siemens SMART CCD diffractometer with graphite
monochromated Mo Kα radiation (λ=0.71073 Å) at 298 K. An em-
pirical absorption correction was applied using the SADABS program.
The structures were solved by direct methods and refined by full-matrix
least-squares methods on F2 by using the SHELX-97 program package
[27]. All non-hydrogen atoms were refined anisotropically. Hydrogen
atoms of PyHBIm were generated geometrically, and no attempts were
made to locate the hydrogen atoms of water.
Fig. 5. Solid-state emission spectra of 1–3 at room temperature.

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