A tetrazolate-based coordination complex with novel 3D structure and catalytic property

Article abstract of DOI:10.1016/j.inoche.2013.03.016

Hydrothermal reaction of 5-(4-nitrophenyl)-2H-tetrazole [H(4-nptz)] and CuCl generates a novel complex Cu(4-nptz). In complex (1), the tetrahedral Cu(I) cations are linked by μ₄-4-nptz ligands into a 4-connected 3D framework with sra topology.

Full text of DOI:10.1016/j.inoche.2013.03.016

Inorganic Chemistry Communications 33 (2013) 158–160
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
A tetrazolate-based coordination complex with novel 3D structure and
catalytic property
⁎
⁎
Pei-Jiang Liu, Dong-Sheng Ma , Dan Xiao, Guang-Feng Hou
School of Chemistry and Materials Science, Heilongjiang University, Harbin 150080, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Hydrothermal reaction of 5-(4-nitrophenyl)-2H-tetrazole [H(4-nptz)] and CuCl generates a novel complex
Cu(4-nptz). In complex (1), the tetrahedral Cu(I) cations are linked by μ4-4-nptz ligands into
Received 14 January 2013
Accepted 18 March 2013
Available online 12 April 2013
a
4-connected 3D framework with sra topology. Complex (1) represents the first 3D structure constructed
by 4-nptz ligand, and it is insolvable in all solutions and stable in room temperature. However, it will explode
when the temperature is higher than 360 °C. UV–vis diffuse reflectance spectroscopy (DRS) of complex (1)
exhibits a strong absorption band in the visible light region around 750 nm. In addition, complex (1) exhibits
catalytic property to the hydrolysis of ester.
Keywords:
Metal–organic framework
Tetrazole
Crystal structure
Catalysis
© 2013 Elsevier B.V. All rights reserved.
The design and assembly of metal–organic frameworks (MOFs)
have attracted great interests over recent years, because of their in-
triguing architectures as well as the potential applications in catalysis,
magnetism, luminescence, ion exchange, and gas storage [1–4]. As it
is well known, the choice of organic ligands is one of the most crucial
factors for the construction of novel topological structures. A compre-
hensive research of MOFs built on tetrazoles and their derivatives has
witnessed tremendous attention since the preparation of the first
tetrazole complex by the Bladin in 1885 [5]. The multi nitrogen
atoms of tetrazoles and their derivatives endow them rich coordina-
tion modes to act as either a multidentate or a bridging building
block for constructing high dimensional frameworks with a wide di-
versity of topologies [6–10].
5-(4-Nitrophenyl)-2H-tetrazole [H(4-nptz)] possesses one tetrazolate
ring and one nitro group, which represents a significant multidentate
tetrazolate ligand to synthesis MOFs. However, the H(4-nptz) ligand has
not been well exploited in building coordination complexes, only one rel-
evant report is available up to date [11]. In our attempt to synthesize high
dimensional coordination polymer based on H(4-nptz) and d10 metal
Cu(I), a novel complex, Cu(4-nptz) (1) with 3D sra framework was
obtained. In addition, it exhibits catalytic property to the hydrolysis of
ester. To our best knowledge, it represents the first 3D structure
constructed by 4-nptz ligand.
composed of one Cu(I) cation and one 4-nptz ligand. The Cu1 ion is
four-coordinated in a distorted tetrahedron geometry defined by three
N atoms and one O atom from four different 4-nptz ligands with the
Cu\N bond lengths of 1.969(2)–2.046(2) Å and Cu\O = 2.477(2) Å
(Fig. 1) respectively.
In the crystal packing, initially, the tetrazolate group of the 4-nptz
ligand serves as a tridentate bridging linker, which coordinates with
three different Cu(I) cations to form a 2D layer {tetrazole-Cu} moie-
ty. It can be seen as a fes-type network, when the tetrazolate group is
reduced as a 3-connected node. Furthermore, the nitro group of
4-nptz ligand takes part in the coordination of Cu(I) cation, which
links the adjacent 2D layer to form a 3D framework (Fig. 2). The
4-nptz-based metal complexes, [Cd(H2O)2(4-nptz)2]·2(H2O) and
[Cd(H2O)2(4-nptz)2], were first reported in 2009 [11], in which the
nitro group acts as an accepter of hydrogen bonds instead of coordi-
nation group to form low dimensional structures. To our best knowl-
edge, the reports about nitro groups of aromatic compounds
coordinating with transition metals are relatively rare.
In the 4-nptz molecule, the nitrophenyl group twists out of the
tetrazolate plane with a dihedral angle of 34.9(2)°. If 4-nptz molecule
is assigned as a 4-connected nodes, the 3D structure of complex (1)
could be regarded as a uninodal 4-c framework of sra-type topology
(also called SrAl2, CeCu2 and ABW) with the Schlafli symbol of (42;
63; 8) (Fig. 3) [16].
The hydrothermal reaction of CuCl and H(4-nptz) at 140 °C for
3 days produced red brown needle-like crystals [12,13]. Single-crystal
X-ray diffraction analysis reveals that complex (1) crystallizes in mono-
clinic system with P21/c space group [14,15]. The asymmetric unit of 1 is
The molar conductivity measurements, XPS, PXRD and TGA are car-
ried out to investigate the purity and stability of complex (1). The molar
conductivity value recorded 12.9 S cm2 mol−1 in DMSO solution at
room temperature confirm that complex (1) is non-electrolyte and
therefore remained neutral and do not undergo ligand exchange with
the solvent during the timeframe of the conductivity measurement
[17]. The XPS spectra of complex (1) are shown in Figure S2 in
⁎
Corresponding authors. Tel.: +86 451 86609001; fax: +86 451 86609151.
E-mail address: RWWS8828@sina.com (D.-S. Ma).
1387-7003/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.inoche.2013.03.016

P.-J. Liu et al. / Inorganic Chemistry Communications 33 (2013) 158–160
159
Fig. 2. 3D framework formed by the nitro group coordinating with 2D {tetrazole-Cu}
moieties.
Fig. 1. Asymmetric unit of complex (1) with thermal ellipsoids presented at the 50%
probability level. Symmetry code: (I) x, 0.5 − y, −0.5 + z; (II) 2 − x, 0.5 + y,
0.5 − z; (III) 1 + x, 0.5 − y, 0.5 + z.
In conclusion, a novel complex, Cu(4-nptz) 1 [4-nptz = 5-(4-
nitrophenyl)-2H-tetrazole], is synthesized and structurally character-
ized. In complex (1), the 4-nptz ligands act as μ4-linkages bridging the
Cu(I) ions to form a 3D framework with the sra topology. The nitro
group of the 4-nptz ligand takes part in the coordination, such coordina-
tion model of nitro containing compounds is rarely observed, which
plays an important role in the formation of high dimensional structure
of complex (1). Complex (1) is unsolvable in all solutions and stable in
room temperature. However, it will explode when the temperature is
higher than 360 °C. The catalytic experiment exhibits that complex (1)
could reduce the reaction time and improve the product yield in the hy-
drolysis of 4-nitrophenyl acetate.
Supporting information. The spin-orbit components (2p3/2 and 2p1/2) of
Cu2P peaks were documented at 931.9 and 951.7 eV with a spin-orbit
separation of 19.8 eV. It confirms the presence of Cu(I) in complex (1)
[18,19]. The result of PXRD shows that the peak positions and their in-
tensities are consistent with the simulated pattern, indicating the
phase purity of complex (1) (Fig. S3). TGA experiments were carried
out under N2 atmosphere to determine the thermal stabilities of com-
plex (1). TGA shows complex (1) can be stable to 360 °C. The UV–vis
diffuse reflectance spectroscopy (DRS) of complex (1) was carried out
using a Cary 5000 UV–vis-NIR analyzer. As shown in Fig. S4, complex
(1) exhibits a strong absorption band in the visible light region around
750 nm possibly due to LMCT transition [20], resulting in the red brown
color of the complex (1).
Acknowledgment
We acknowledge the support of the Natural Science Foundation of
Heilongjiang Province (B201108) and Science and Technology Plan-
ning Project of Heilongjiang Province (WJ09B03). We thank Heilong-
jiang University for supporting this study.
Though a great number of MOFs have been reported over the past
decade, their application as homogeneous or heterogeneous catalysts
is relatively rare. Considering practical advantages of easy handling
and simple separation from the reaction system, we have examined
the synthesized of complex (1) act as potential heterogeneous cata-
lyst for the hydrolysis of 4-nitrophenyl acetate (Eq. (1)) [21].
Appendix A. Supplementary material
CCDC 918204 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Fig. S1–S4 can be found in the supporting file. Sup-
plementary data to this article can be found online at http://dx.doi.
org/10.1016/j.inoche.2013.03.016.
ð1Þ
All products were determined by high performance liquid chro-
matography (HPLC), compared with authentic samples. Complex
(1) can enhance the hydrolysis speed of 4-nitrophenyl acetate ap-
proximately 3 times when reacting for 30 min compared with blank
experiment. After 2 h, the 4-nitrophenyl acetate could completely
be converted to 4-nitrophenol with complex (1) acting as catalyst.
However, in the blank experiment, 38% 4-nitrophenyl acetate is still
remained unreacted. This observation encourages us to construct
new MOFs that might be efficiently used as heterogeneous catalysts
friendly to the environment.
Fig. 3. Schematic illustration of 3D 4-connected sra type topology framework with a
Schlafli symbol of (42; 63; 8).

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P.-J. Liu et al. / Inorganic Chemistry Communications 33 (2013) 158–160
stainless steel vessel under autogeneous pressure. After slow cooling to room
References
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