catena-Poly[[octaaquabis(μ4-benzene-1,3,5-tricarboxylato)trizinc] tetrahydrate]

In the title compound, {[Zn3(C9H3O6)2(H2O)8]·4H2O}n, there are two crystallographically independent ZnII ions. One presents a trigonal-bipyramidal coordination geometry defined by five O atoms [three from two carboxylate groups of two benzene-1,3,5-tricarboxylate (BTC) ligands and the other two deriving from three water molecules], while the other lies on an inversion centre and exists in a slightly distorted octahedral coordination geometry defined by six O atoms (two from two carboxylate groups of two BTC ligands and the others from four water molecules). A three-dimensional framework is further strengthened via O—H⋯O hydrogen-bonding interactons.

In the title compound, {[Zn 3 (C 9 H 3 O 6 ) 2 (H 2 O) 8 ]Á4H 2 O} n , there are two crystallographically independent Zn II ions. One presents a trigonal-bipyramidal coordination geometry defined by five O atoms [three from two carboxylate groups of two benzene-1,3,5-tricarboxylate (BTC) ligands and the other two deriving from three water molecules], while the other lies on an inversion centre and exists in a slightly distorted octahedral coordination geometry defined by six O atoms (two from two carboxylate groups of two BTC ligands and the others from four water molecules). A threedimensional framework is further strengthened via O-HÁ Á ÁO hydrogen-bonding interactons.

Comment
The exploring of metal-organic frameworks (MOFs) has attracted considerable attention not only owing to their intriguing structral architectures and topologies, but also because of their many potential applications in catalysis, ion exchange, and magnetic, optical, and porous materials (Batten & Murray, 2003;Zhong et al., 2008;Qiu et al.,2010). 1,3,5-benzenetricarboxylate with six O atoms from its three carboxylate groups is a good choice of O-donor ligand. And such ligand has been widely used to synthesize metal compounds (Yaghi et al., 1997;Xu et al., 2008;Xu et al., 2007;Liang et al., 2009;Wang et al., 2009). Thus, we synthesize a new three-dimensional Zn-BTC metal-organic compound, with achiral channels along b direction, which was generated by the reaction of zinc sulfate heptahydrate, 1,3,5-benzenetricarboxylic acid and water at 150°C for 3 days.
There are two kinds of zinc atoms in the title compound (I) (Fig. 1). One is surrounded by five O atoms (three from two carboxylate groups of two BTC ligands and the other two deriving from three water molecules), exhibiting a trigonal bipyramidal geometry, the other is coordinated with six O atoms (two from two carboxylate groups of two BTC ligands; the others from four water molecules) and displays a slightly distorted octahedral geometry. All the BTC ligands have the same coordinated modes and each ligand coordinated to three zinc atoms. The bond distances of Zn-O chelated carboxylate range from 1.999 (5)Å to 2.412 (6) Å. While the bond lengthes of Zn-O monodentate carboxylate fall between 1.946 (6)Å and 2.049 (5) Å. And the Zn-O w distances are in the normal range of 1.965 (6)-2.150 (6)Å (Table 1). All the distances of Zn-O in compound (I) are comparable to those found in the literatures (Hua et al., 2010;Chen et al., 2010;Yang et al., 2008;Xu et al., 2007). And there are weak interactions between Zn1 and C1 with the distances of 2.554Å and Zn1 and H2WB with with the distances of 2.0711 Å. A three-dimensional architecture is strengthened by the extended O-H···O hydrogen-bonding interactions (

Experimental
A mixture of zinc sulfate heptahydrate (0.287 g; 1 mmol), benzenetricarboxylic acid (0.210 g; 1 mmol) and water (10 ml) was sealed in a 23 ml Teflon-lined stainless steel reactor and heated at 120°C under autogenous pressure for 72 h. Then the mixture was cooled down to room temperature at a rate of 5°C per hour, and colorless block crystals were obtained in a yield of 49% based on Zn Refinement water H atoms were located in a difference Fourier map and were refined isotropically, Other H-atoms on aromatic ring were placed in calculated positions with C-H = 0.93 Å; refined using a riding model with U iso (H) = 1.2 U eq (C).
supplementary materials sup-2 Figures   Fig. 1. The structure of (I), showing the atomic numbering scheme. Non-H atoms are shown as 30% probability displacement ellipsoids.