CHEN Shun-Yu YANG E, ZHANG Jin (College of Chemistry & Chemicl Engineering,Fujin Norml University, Fuzhou 350007, Chin) (Stte Key Lortory of Structurl Chemistry, Fujin Institute of Reserch on the Structure of Mtter, Chinese Acdemy of Sciences, Fuzhou 350002, Chin)

1 INTRODUCTION

The design and synthesis of metal-organic frameworks (MOFs) have been paid great attention and developed rapidly in recent years owing to their intriguing structural topologies and potential applications as functional materials[1-6]. To design a new building block, the geometries of the constituent metal cations and bridging ligands are the keynotes.Our strategy is based upon the coordination of a d10block metal Zn(II) with an aromatic multicarboxylate ligand. The high symmetry 1,2,4,5-benzenetetracarboxylic acid (H4btec) molecule has been shown to be a good building block in the construction of metal-organic compound owing to its rich coordination modes. It can coordinate to metal ions through complete or partial deprotonation of its four carboxyl groups. A series of btec-based compounds with interesting structures have been successfully obtained[7-15]. However, the formation of coordination polymers is influenced by many factors such as solvents, templates, pH value, reaction temperature and so on, so we can construct novel compounds by changing reaction conditions. In this paper, we report the synthesis and crystal structure of a novel Zn(I)-btec compound, namely [Zn3(btec)(OH)2(H2O)2]n(1).

2 EXPERIMENTAL

2.1 Materials and instruments

All reagents were purchased commercially and used without further purification. Crystal structure determination was carried out on a Bruker SMART diffractometer.

2.2 Synthesis of [Zn3(btec)(OH)2(H2O)2]n (1)

Zn(NO3)2·6H2O (0.1507 g), Na2CO3(0.0530 g),1,2,4,5-benzenetetracarboxylic acid (0.1504 g) and distilled water (6 mL) were mixed in a 23 mL Teflon cup and the mixture was stirred for 20 min. The vessel was then sealed and heated at 150 ℃ for 5 days. The autoclave was allowed to cool to room temperature. Transparent colorless crystals were obtained.

2.3 Crystal structure determination

A colorless single crystal of the title compound was selected and mounted on a glass fiber. Diffraction data were collected at 293(2) K on a Bruker SMART diffractometer equipped with a graphitemonochromatic MoKα radiation (λ = 0.71073?). A total of 1916 reflections were collected in the range of 2.44＜θ＜25.01° by using an ω scan mode, of which 1146 were unique with Rint= 0.0311 and used in the succeeding structure calculations. The structure was solved by direct methods and explained with Fourier techniques.

All non-hydrogen atoms were located by direct methods and subsequent difference Fourier syntheses[16-17], and the hydrogen atoms were located according to geometrical calculations. All non-hydrogen atoms were refined by full-matrix leastsquares techniques for 1110 observed reflections with I ＞ 2σ(I) to the final R = 0.0590, wR = 0.1279(w = 1/[σ2(Fo2) + (0.0284P)2+ 66.2700P], where P =(Fo2+ 2Fc2)/3), S = 1.001 and (Δ/σ)max= 0.000. The highest and lowest residual peaks in the final difference Fourier map are 1.001 and –1.057 e/?3,respectively.

3 RESULTS AND DISCUSSION

The selected bond lengths and bond angles of compound 1 are listed in Table 1. Single-crystal X-ray diffraction analysis reveals that compound 1 features a three-dimensional framework with pillared layer structure. As shown in Fig. 1, the asymmetric unit of the title compound contains two crystallographically unique Zn(II) atoms. The two Zn(II) atoms show different coordination environments. The Zn(1) atom is four-coordinated by two bridging carboxylate oxygen atoms (O(1), O(1a))from two different btec ligands and two oxygen atoms of two symmetry-related water molecules,forming a tetrahedral coordination geometry. Differently, the Zn(2) atom is bound to one water molecule, one OH-group and four carboxylate oxygen atoms (O(2), O(3c), O(4c), O(4b)) from three different btec ligands to form a coordination octahedron. It is interesting to note that the four carboxylate groups of each btec ligand anion show different coordination modes. Two carboxylate groups adopt a chelating-bridging coordination mode, while the other two adopt a bidentate-bridging mode. As such, Zn(1) and Zn(2) atoms are connected through the bridging carboxylate oxygen atoms of btec ligands and μ2-bridging oxygen atoms of water molecules to generate an infinite one-dimensional chain along the a axis. The adjacent chains are linked together through the benzene rings of btec ligands to generate a two-dimensional polymeric network parallel to the ac plane, as described in Fig. 2.The resulting layers are further linked by the benzene rings of btec ligands to give the final three-dimensional structure. The benzene rings act as pillars between two layers (Fig. 3).

Table 1. Selected Bond Lengths (?) and Bond Angles (°) of the Title Compound

Fig. 1. Asymmetric unit of 1 showing the coordination environment of Zn(1) and Zn(2) atoms and the coordination mode of btec ligand. Symmetry codes: (a) –x, y, –z+1/2; (b) x, –1+y, z;

Fig. 2. (a) One-dimensional infinite chain structure of complex 1;(b) 1D chains are contacted to yield a 2D networkparallel to the acplane

Fig. 3. 3D structure of complex 1(Hydrogen atoms are omitted for clarity)

4 CONCLUSION

A new zinc complex, [Zn3(btec)(OH)2(H2O)2]n(1),has been synthesized under the hydrothermal condition and structurally characterized by X-ray diffraction analysis. Complex 1 exhibits a threedimensional framework with pillared layer structure.The structural feature of 1 is that the crystallographically unique Zn(II) atoms are connected through the bridging carboxylate oxygen atoms of the btec ligands and μ2-bridging oxygen atoms of water molecules to generate an infinite 1-D chain. The adjacent chains are linked together through the benzene rings of btec ligands to form 2-D polymer layers which are further linked by the benzene rings of btec ligands to form the final 3-D network. The benzene ring plays a crucial role in forming the multidimensional architecture of complex 1.

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