A heteropolytungstate zigzag chain constructed from Keggin clusters and transition metal complex——Synthesis and structure

LI Jie, GUO Jingyu

(College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, Henan, China)

AheteropolytungstatezigzagchainconstructedfromKegginclustersandtransitionmetalcomplex
——Synthesis and structure

LI Jie*, GUO Jingyu

(CollegeofChemistryandChemicalEngineering,HenanUniversity,Kaifeng475004,Henan,China)

A one-dimensional (denoted as 1D) zigzag chain of organic-inorganic hybrid heteropolytungstate, [Cu(en)2(H2O)]{[Cu(en)2(H2O)][Cu(en)2](α-SiW12O40)}(OH)2·H2O (en = 1, 2-ethylenediamine), denoted as1, has been prepared under mild hydrothermal conditions. As-synthesized 1D zigzag chain organic-inorganic hybrid heteropolytungstate was characterized by elemental analysis, infrared spectrometry and single-crystal X-ray diffraction. Results indicate that as-synthesized product1belongs to triclinic system of space groupP-1, and its crystal data are determined to bea= 1.297 6(6) nm,b= 1.473 5(7) nm,c= 1.909 9(9) nm,α= 86.736(8)°,β= 88.833(8)°,γ= 74.840(8)°,V= 3.519(3) nm3, andZ= 2. In terms of molecular structure, compound1is composed of a familiar Keggin-type anion [a-SiW12O40]4-, two different CuIIcoordination cations [Cu(en)2(H2O)]2+and [Cu(en)2]2+, one discrete copper coordination cation [Cu(en)2(H2O)]2+, two OH-ions and one crystal water molecule. The adjacent [α-SiW12O40]4-polyoxoanions are interconnected together through two coordination cations [Cu(en)2)]2+constructing the 1D zigzag chain architecture.

Keggin cluster; transition metal complex; heteropolytungstate; synthesis; crystal structure

In the last two decades, abundant functionalized organic-inorganic hybrid compounds have been developed based on the combination of polyoxometalates (POMs) with metal-organic coordination polymers. Recently, hybrid POMs have received extensive attention in the crystal engineering, due to their potential applications in catalysis, adsorption, medicine and electronic materials as well as their changeable structural topologies[1-4]. During the development of POM chemistry, organic-inorganic coordination polymers with Keggin-type framework have been found to be of particular significance, and a large amount of metal-organic coordination polymers based on such polyanions have been reported[5-15]. In terms of the molecular structures of the organic-inorganic coordination polymers with Keggin-type framework, the transition-metal coordination complexes not only can provide charge compensation, but also can comprise a part of the inorganic POM framework, thereby enriching the POM-based hybrid chemistry. Since copper as a d-block transition-metal element can act as a bridge to construct multi-dimensional skeleton under mild hydrothermal conditions[11, 14-19], we choose it as a bridge to link Keggin-type anions. In the meantime, considering that N-containing ligands are capable of forming interesting supramolecular structures, and 1, 2-ethylenediamine (denoted as en) as a hydrogen-bonding acceptor and donor is a bidentated ligand, we select rigid ligand en as the organic moiety to construct a new one-dimensional (1D) zigzag chain heteropolytungstate. In this paper we report the hydrothermal synthesis and crystal structure characterization of the 1D zigzag chain heteropolytungstate, [Cu(en)2(H2O)]{[Cu(en)2(H2O)][Cu(en)2](α-SiW12O40)}(OH)2·H2O (coded as1), constructed from Keggin-type polyoxoanion and rigid ligands decorated [Cu(en)2(H2O)]2+and [Cu(en)2)]2+cationic complex.

1 Experiment

1.1 Materials and physical measurements

All reagents were purchased commercially and used without further purification. Elemental analyses (C, H and N) were performed with a Perkin-Elmer 2400-II CHN elemental analyzer. Infrared (IR) spectra of the product powders palletized with KBr were recorded with a Nicolet FT-IR 360 spectrometer in the wavelength range of 400-4 000 cm-1.

1.2 Synthesis of compound 1

A mixture of Na2WO4·2H2O (1.43 g, 4.34 mmol), Na2SiO3(0.06 g, 0.47 mmol), Cu(CH3COO)2·H2O (0.07 g, 0.33 mmol), CuCl2·2H2O (0.13 g, 0.68 mmol), en (0.10 mL),L-arginine (0.08 g, 0.33 mmol) and H2O (15 mL, 684 mmol) was stirred for 2 h and neutralized to pH 5.6-6.5 with 2 mol·L-1HCl solution and 2 mol·L-1NaOH solution. The mixture was then transferred into a Teon-lined autoclave (23 mL) and heated at 160 ℃ for 4 d. Upon completion of the reaction, the reaction solution was slowly cooled to room temperature and filtrated to afford dark green block crystal. The crude product was washed with distilled water to afford target compound1with a yield of 11%. Elemental analysis (%) calculated for C12H58Cu3N12O45SiW12: C 4.10, H 1.66 and N 4.78; found: C 3.98, H 1.95 and N 4.54.

1.3 Single-crystal X-ray diffraction (XRD)

A dark green crystal of compound1with dimensions of 0.48 mm × 0.17 mm × 0.13 mm was mounted to a glass fiber; and the XRD data were collected at 296(2) K with a Bruker Smart Apex-II CCD diffractometer (graphite-monochromated Mo Kαradiation;λ= 0.071 073 nm). A total of 18 237 independent reections were collected, and 12 335 reections withI> 2σ(I) were considered and observed. Direct methods were used to solve the structures and to locate the heavy atoms with the SHELXTL-97 program package[20]. The remaining atoms were found from successive full-matrix least-squares refinements onF2in association with Fourier syntheses. No hydrogen atoms associated with water molecules were located from the difference Fourier map. All hydrogen atoms were refined isotropically in a riding mode with the default SHELXTL parameters. The details for structural analyses of1are summarized in Table 1. Selected bond length ranges for1are given in Table 2. The atomic coordinates and other parameters of structure have been deposited at the Cambridge Crystallographic Data Centre (1007238; deposit@ccdc.cam.ac.uk).

Table 1 Crystal data and structural refinements for compound 1

Table 2 Selected bond lengths for compound 1

2 Results and discussion

2.1 Crystal structure

Compound1synthesized under hydrothermal conditions crystallizes in the orthorhombic space groupP-1. The structural feature of compound1is that it is comprised of saturated Keggin polyoxoanions and metal-organic moieties.

Single-crystal XRD analyses reveal that the molecule of compound1consists of a familiar plenary tridentate [α-SiW12O40]4-polyanion, two different CuIIcoordination cations [Cu(en)2(H2O)]2+and [Cu(en)2]2+, one discrete copper coordination cation [Cu(en)2(H2O)]2+, two OH-ions and one crystal water molecule. In compound1, there are four copper ions (Cu(1), Cu(2), Cu(3) and Cu(4)) with two kinds of coordination models, and the bond valence sum (BVS) calculations[21]allow us to determine the oxidation states of the Cu centers. The BVS values of four copper ions are 1.46, 1.75, 1.47 and 1.72, respectively, which implies that they exhibit the oxidation states of +2. Both Cu(1) and Cu(3) ions (occupation factor: 0.5) reside in five-coordinate tetragonal pyramid geometry composed of four nitrogen atoms from two bidentated ligands (en) and one oxygen atom from the adjacent polyoxoanion [α-SiW12O40]4-. For Cu(1) and Cu(3) ions, the Cu-N distances fall in the ranges of 0.196(3)-0.200(3) nm and 0.197(2)-0.199 0(18) nm, respectively. The Cu(2) ion adopts six-coordinate octahedral geometry whose equatorial plane is defined by four nitrogen atoms (N(3), N(4), N(5) and N(6)) from two chelating en ligands, with the Cu-N distances ranging from 0.198 4(15) nm to 0.202 6(18) nm. An apical position of the octahedron is completed by an oxygen atom of the water molecule O(1w) with a Cu-Ow distance of 0.235 9(15) nm, and the other one by an oxygen atom O(8) of the polyoxoanion [α-SiW12O40]4-. The Cu(4) ion also displays tetragonal pyramid geometry. The equatorial plane of Cu(4) center is defined by four nitrogen atoms (N(9), N(10), N(11), and N(12)) from two en ligands, with the Cu-N distances ranging from 0.192(2) nm to 0.202(2) nm, however, the apical position comes from an oxygen atom of the water molecule O(2w) with a Cu-Ow distance of 0.233 5(15) nm.

The polyoxoanion of1shows a typicalα-Keggin configuration, which is made up of twelve WO6octahedrons and one SiO4tetrahedron. In the tridentate [α-SiW12O40]4-polyanion, the central Si atom exhibits tetrahedral coordination mode with a Si-O bond length of 0.160 6(10)-0.163 6(11) nm. All W centers exhibit a WO6octahedral environment. Generally, twelve WO6octahedrons may be sub-divided into four groups of W3O13triads which are composed of three edge-sharing WO6octahedrons linked in a triangular arrangement. Four groups of such W3O13triads are linked together by sharing corners, in turn, and linked to the SiO4tetrahedron by the three-coordinated oxygen atoms (see Fig. 1). According to the coordination numbers and types, the W-O distances can be grouped into three sets: W-Oa(central) 0.237 8(9)-0.271(11) nm, W-Ob(c)(bridge) 0.184 3(11)-0.199 6(11) nm and W-Ot(terminal) 0.165 1(13)-0.174 4(11) nm, respectively. And the W-O-W bond angles change from 73.4(4)° to 174.0(6)°.

The hydrogen atoms and lattice water molecules are omitted for clarity.Fig.1 Ball-and-stick view of the structural unit of compound 1

The adjacent [α-SiW12O40]4-polyoxoanions are interconnected together through rigid ligand decorated by [Cu(en)2)]2+cationic complex, constructing a 1D zigzag chain architecture (Fig.2).

2.2 IR spectrum

In the IR spectrum of compound1, there are four characteristic peaks of POMs: 1 013 cm-1attributed toν(Si-Oa), 965 cm-1ascribed toν(W-Ot), 880 cm-1assigned toν(W-Ob-W), and 798 cm-1assigned toν(W-Oc-W). This means that the polyoxoanion in1still retains the saturatedα-Keggin-type structure[22]. In addition, the characteristic peaks from 1 053 cm-1to 1 562 cm-1are attributed to the rigid ligands en, and the peaks at 3 326 and 3 431 cm-1are assigned toν(N-H) of en molecules andν(O-H) of the water molecules, respectively.

Fig.2 View of the 1D zigzag chain constructed by alternate [α-SiW12O40]4- polyoxoanions and [Cu(en)2]2+ coordination cations in compound 1 along a-axis. The hydrogen atoms, lattice water molecules and free coordination cations [Cu(en)2(H2O)]2+ are omitted for clarity

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由Keggin型簇和过渡金属配合物构筑的杂多钨酸盐锯齿链的合成和结构

李 杰*，郭静玉

(河南大学 化学化工学院，河南 开封 475004)

采用水热法合成了一维锯齿链状的有机-无机杂化杂多钨酸盐[Cu(en)2(H2O)]{[Cu(en)2(H2O)][Cu(en)2](α-SiW12O40)}(OH)2·H2O (记作1；en = 1, 2-乙二胺)；利用元素分析、红外光谱和X 射线单晶衍射对其结构进行了表征. 结果表明，化合物1属于三斜晶系，P-1空间群；其晶格参数为：a= 1.297 6(6) nm,b= 1.473 5(7) nm,c= 1.909 9(9) nm,α= 86.736(8)°,β= 88.833(8)°,γ= 74.840(8)°,V= 3.519(3) nm3，Z= 2. 就分子结构而言，化合物1由一个常见的Keggin型多阴离子[α-SiW12O40]4-、两个不同的铜配位阳离子[Cu(en)2(H2O)]2+和[Cu(en)2]2+、一个游离的铜配位阳离子[Cu(en)2(H2O)]2+、两个氢氧根离子和一个结晶水组成；相邻的[α-SiW12O40]4-多阴离子通过两个配位阳离子[Cu(en)2)]2+相连，形成一维锯齿链状结构.

Keggin簇；过渡金属配合物；杂多钨酸盐；合成；晶体结构

date：2014-06-10.

河南省教育厅科学技术研究重点项目 (12A150004).

Biography：李 杰(1978-)，女，高级实验师，研究方向为多酸化学.*

，E-mail：lllijie2007@henu.edu.cn.

O 627.12DocumentcodeAArticleID1008-1011(2014)06-0573-06

10.14002/j.hxya.2014.06.005