Inorganic Chemistry Communications 31 (2013) 1–4

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Inorganic Chemistry Communications

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Unprecedented preparation of a unique 2D multinuclear copper metal-tetrazolepolymer by in situ solvothermal reaction: Crystal structure and magnetic property

Jiehu Cui a,⁎, Hui Zhao b, Junwei Zhao c

a College of Civil Engineering and Architecture, Zhengzhou Institute of Aeronautical Industry Management, Zhengzhou 450015, P.R. Chinab Department of Chemistry, Zhoukou Normal University, Zhoukou 466001, P.R. Chinac College of Chemistry and Chemical Engineering, Henan University, Kaifeng, Henan 475001, P.R. China

⁎ Corresponding author. Tel./fax: +86 394 8178253.E-mail addresses: cuijiehu@163.com, sunvalley99@1

1387-7003/$ – see front matter © 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.inoche.2013.02.009

a b s t r a c t

a r t i c l e i n f o

Article history:Received 31 December 2012Accepted 7 February 2013Available online 16 February 2013

Keywords:Multinuclear copperIn-situ reactionMagnetic property

A novel coordination complex {[Cu14(pytz)8(CN)10(H2O)2]·H2O}n (1, Hpytz=5-(2-pyridyl)-2H-tetrazole) hasbeen synthesized by the hydrothermal reaction of Cu(NO3)2 with Hpytz ligand in mixed CH3CN/H2O solutionunder 150 °C. The cyanide may be generated in situ from the C–C cleavage of acetonitrile under hydrothermalconditions. Complex 1 consists of an infinite 2D network with CN− and pytz− ligand bridges. Magnetic suscep-tibility measurement indicates that 1 shows antiferromagnetic interaction between the adjacent Cu(II) ions.

© 2013 Elsevier B.V. All rights reserved.

In recent years, the study of polynuclear transition metal complexeshas offered promising perspectives toward developing new functionalmaterials. A promising strategy for the construction of polynuclear sys-tems is the self-assembly approach of organic/inorganic components, inwhich inorganic elements are linked by organic bridges, therefore, theresearch on coordination polymers (CPs) has been rapidly expandeddue to their rich structural characteristics, interesting properties andpotential applications [1]. In order to synthesize novel coordinationpolymers, the key is the design and selection of bridging ligands. Thecyano ligand plays an important role in the design of low dimensionalmagnetic coordination polymers because it is a good superexchangepathway between the paramagnetic metal ions [2].

The hydrothermal method has been proved to be a promising tech-nique in constructing novel coordination polymers [3]. More attentionis paid on its simple methodology, low cost and the polytrope of chemi-cal changes accompanying reduction and oxidation processes [4]. More-over, some unique inorganic or organic reactions [5,6] can be foundunder this condition. Among those polymers, self-assembly reaction ofmetal cations with nitrogen heterocyclic bridging ligands has receivedmuch attention because of their applications in heterogeneous catalysis,molecular recognition, chemical sensors and gas storage [7–9]. Due to itsaromaticity and multiple N-donor atoms, 5-(2-pyridyl)-2H-tetrazole(Hpytz) is a particularly promising candidate in the construction of coor-dination frameworks.

Keeping in mind the aforementioned points, we employ Hpytz asthe nitrogen heterocyclic bridging ligand to react with Cu2+ ionunder hydrothermal reactions, hoping to explore the influence on

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the structures of the products. In this context, a novel coordinationcomplex {[Cu14(pytz)8(CN)10(H2O)2]·H2O}n (1, Hpytz=5-(2-pyridyl)-2H-tetrazole) has been synthesized and characterized.

Compound 1 [10] was synthesized hydrothermally by treatingCu(NO3)2 and Hpytz at 150 °C. X-ray crystal analysis reveals (TableS1) that 1 crystallizes in the triclinic space group P-1 and the asymmet-rical unit contains seven Cu(II) ions. As shown in Fig. 1, the Cu1 ion isfive-coordinated by one oxygen atom from the water molecule, andfour nitrogen atoms from two pytz− ligands. The bond lengths ofCu\N are in the range of 1.960(6) and 2.048(9)Å. The Cu2 ion isfour-coordinated by four nitrogen atoms from two pytz− ligands withthe Cu\N bond lengths of 1.9442(6)–2.033(9)Å. While the Cu3, Cu5and Cu6 ions are all three-coordinated by two CN− ions and one nitro-gen atom from pytz− ligand with the C\Cu and Cu\N bond lengthsof 1.8488–1.8855 Å and 1.9193–2.1041 Å. The Cu4 ion is three-coordinated by one CN− and two nitrogen atoms from two pytz−

ligands. The Cu7 ion is also three-coordinated by three CN− ligands.The pytz− anions adopt two coordination modes (Scheme 1). Fromthe structural descriptions above, it can be seen that all CuII ions havedifferent coordinated modes.

Cyanometallates are useful building blocks for the construction ofsupramolecular structures. Such supramolecular assemblies are usu-ally achieved through bridging linear covalent M\CN\M bonding in-teractions [11]. The most intriguing structural feature of 1 is that itsunusual supramolecular interactions between M–CN–M and pytz−

anions generate a unique 2D supramolecular architecture in thesolid state (Fig. 2).

The IR spectrum of 1 is in agreement with the proposed structureshown in Fig. 1. The IR spectrum of 1 shows absorption bandsresulting from the skeletal vibrations of the aromatic ring in the

Fig. 1. The asymmetrical unit of 1. The H atoms are omitted for the sake of clarity.

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1400–1600 cm−1 regions. The band at 2111 cm−1 can be assigned tothe ν(CN) stretching vibration of the CN− species (Fig. S1). The ν(CN)stretching vibration shifts to the higher energy than that (2080 cm−1)[11] of free cyanide ion in water due to the couple between CN− andtwo metal centers.

The selective cleavage of carbon–carbon bond of acetonitrile by ho-mogeneous transition metals remains a significant challenge for organ-ometallic chemistry [12]. The majority of successful C–CN cleavagereactions use relief of strain, proximity, or achievement of aromaticityas the driving force for the reaction [13]. Recently, some advancementshave been achieved in the area of C–CN cleavage through the otherdriving forces, for example, oxidative addition, electrophilic additionand photolysis [14]. Besides, Tong [15] and Chen [11] have successfullyrealized the cleavage of C\CN bond of acetonitrile by temperature asthe driving force. In this paper, cyanides are occurred in 1, which maybe due to the cleavage of the C\CN bond of acetonitrile in solvothermalconditions (150 °C and autogenous pressure). The observation of C–CNcleavage through solvothermal condition is particularly impressive,further investigation for the mechanism is still under way in our lab.

To confirm whether the crystal structure is truly representative ofthe bulk materials, XRD experiment was carried out for the complex.The experimental and simulated XRD patterns of the complex areshown in Fig. S2, and the results show that the bulk synthesized ma-terials and the measured single crystal are the same.

To estimate the stability of 1, its thermal behaviorwas carried out byTGA in flow of N2 in the temperature range from 20 to 600 °C (Fig. S3)with a heating rate of 10 °C·min−1. The TGA curve indicates that 1starts to lose two coordinationwatermolecules and one freewatermol-ecule, and ends at about 285 °C (the lost weight is 2.36%, calculatedvalue is 2.27%). After the loss of all the water molecules, the supramo-lecular framework is stable up to 320 °C, followed by another weightloss at high temperature. The thermal decomposition feature of 1 is ingood agreement with its crystal structure.

Scheme 1. Two coordination modes of pytz− in 1.

The frameworks of Cu(II) centers (1) provide a good opportunityfor investigating an effective magnetic property through CN− andpytz− bridges. The variable-temperature magnetic susceptibilitymeasurement of 1 was performed in the temperature range of2–300 K. The temperature dependence of the magnetic susceptibilityof 1 in the form of χm and χmT versus T is displayed in Fig. 3.According to the preceding structure description of 1, no appropriatemodel could be used to fit its magnetic properties. At room tempera-ture, χm is equal to 0.01675 cm3 mol−1, upon lowering the tempera-ture, χm continuously increases and reaches 0.7757 cm3 mol−1 at2.0 K. However, χmT versus T curve shows a monotonic decreasefrom room temperature down to 2.0 K, and the value of χmT at300 K is 5.024 and 1.437 cm3 mol−1 K at 2 K, which is similar tothe reported literatures [2b, 16]. This behavior of the complex indi-cates predominant antiferromagnetic interactions within Cu(II) ions.Above 100 K, the magnetic data of 1 obey the Curie–Weiss law andgive C=9.52 cm3 mol−1 K and θ=−273.12 K (Fig. S4). The negativeθ values indicate antiferromagnetic interactions between neighboringCu(II) ions by CN− and pytz− bridges. While separation was bridgedthrough the long spacer ligands pytz−, it should exclude an efficient di-rect exchange between Cu(II) centers (5.97 Å), therefore, the overallantiferromagnetic interactions should be mainly attributed to the CN−

bridges between Cu(II) centers (4.94 Å) in 1.In summary, the present paper reports the hydrothermal synthesis,

crystal structure, thermal stability and magnetic property of a novelunique 2D multinuclear copper. The thermal stability of the complexwas studied, which agreed well with its component. The magneticproperty of the complex shows the presence of antiferromagnetic inter-action mediated by CN− and pytz− bridges. Thus, it may provide auseful strategy for synthesizing new coordination materials.

Acknowledgments

We are grateful to the National Natural Science Foundation ofChina (no. 21101055).

Appendix A. Supplementary data

X-ray crystallographic file in CIF format for compound 1 is avail-able in the supporting material section. CCDC 912125 contains thesupplementary crystallographic data for 1. The data can be obtainedfree of charge from The Cambridge Crystallographic Data Centrevia http://www.ccdc.cam.ac.uk/data_request/cif. Additional structur-al figure, scheme, H-bond data and IR spectrum are available as elec-tronic supplementary information in the online version, at http://dx.doi.org/10.1016/j.inoche.2013.02.009.

Fig. 2. View of the 2D net structure of 1 along the a axis.

Fig. 3. Temperature dependence of magnetic susceptibility in the forms of χm and χmTfor 1.

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