Bis[3-(2-carboxyethenyl)pyridinium-1-acetato]dichloridozinc(II)

In the title complex, [ZnCl2(C10H9NO4)2], the ZnII ion lies on a twofold rotation axis and is four-coordinated by two carboxylate O atoms from two 3-(2-carboxyethenyl)pyridinium-1-acetate ligands in a monodentate mode and two Cl atoms in a distorted tetrahedral geometry. In the crystal structure, intermolecular O—H⋯O hydrogen bonds link the molecules into a double-chain structure extending parallel to [101].

In the title complex, [ZnCl 2 (C 10 H 9 NO 4 ) 2 ], the Zn II ion lies on a twofold rotation axis and is four-coordinated by two carboxylate O atoms from two 3-(2-carboxyethenyl)pyridinium-1-acetate ligands in a monodentate mode and two Cl atoms in a distorted tetrahedral geometry. In the crystal structure, intermolecular O-HÁ Á ÁO hydrogen bonds link the molecules into a double-chain structure extending parallel to [101].

Comment
As we know, hydrogen bond is the most important of all directional intermolecular interactions. It is operative in determining molecular conformation, molecular aggregation, and the function of a vast number of chemical systems ranging from inorganic to biological (Beatty, 2003;Liu et al., 2008;Steiner, 2002). In this paper, we report the coordination and hydrogenbond structure of the title complex derived from a zwitterionic dicarboxylic ligand, 1-carboxymethylpyridinium-3-acrylic acid. Zwitterionic dicarboxylic acids as ligands have received less attention in coordination chemistry than the common dicarboxylic acids, although an increasing number of coordination compounds with such ligands have been reported in recent years (Mao et al., 1999;Wu et al., 2006;Zhang et al., 2002).
The molecular structure is shown in Fig. 1. The Zn II ion, lying on a twofold rotation axis, is coordinated by two Cl atoms and the two zwitterionic ligands through carboxylate O atoms, with a distorted tetrahedral coordination geometry.
The Zn-Cl and Zn-O distances lie in the usual range for a tetrahedral Zn II center ( Table 1) Table 2). The hydrogen bond involves the acrylic hydroxyl group (O4-H4B) from one molecule and the uncoordinated acetate O atom (O2) from another molecule.

Experimental
The zwitterionic ligand was synthesized from ethyl pyridine-3-acrylate and ethyl bromoacetate according to the procedure for similar compounds (Mao et al., 1999). A mixture of the ligand (0.021 g, 0.10 mmol), ZnCl 2 (0.014 g, 0.10 mmol), NaN 3 (0.026 g, 0.40 mmol), ethanol (1.0 ml) and H 2 O (2.0 ml) was sealed in a Teflon-lined autoclave and heated at 343 K for 3 d, then cooled to room temperature at a rate of 5 K h -1 , giving a pale yellow solution. Slow evaporation of the solution at room temperature for several days afforded colorless block crystals of the title compound (yield 46%

Refinement
H atoms attached to C atoms were placed at calculated positions and refined as riding atoms, with C-H = 0.93 (CH) and 0.97 (CH 2 ) Å and with U iso (H) = 1.2U eq (C). The carboxylic H atom (H4B) was located from a difference Fourier map and refined isotropically.