catena-Poly[[bis(1-ethyl-1H-imidazole-κN 3)cadmium]-di-μ-chlorido-[(1-ethyl-1H-imidazole-κN 3)cadmium]-di-μ-chlorido-[(1-ethyl-1H-imidazole-κN 3)cadmium]-di-μ-chlorido-[bis(1-ethyl-1H-imidazole-κN 3)cadmium]]

The asymmetric unit of the crystal structure of the title compound, [Cd2Cl4(C5H8N2)3]n, contains two CdII cations, three 1-ethyl-1H-imidazole ligands, and four Cl− anions. The two CdII atoms have quite different coordination environments: one is octahedrally coordinated by four Cl atoms and two N atoms from two 1-ethyl-1H-imidazole ligands, and the second is in a severely distorted fivefold coordination by four Cl atoms and one N atom from a 1-ethyl-1H-imidazole ligand. Adjacent CdII cations are interconnected alternately by pairs of chloride bridges, generating an infinite step-like chain along the a axis. One ethyl group of the 1-ethyl-1H-imidazole ligand is disordered over two sets of sites with a 0.668 (13):0.332 (13) site-occupancy ratio.

The asymmetric unit of the crystal structure of the title compound, [Cd 2 Cl 4 (C 5 H 8 N 2 ) 3 ] n , contains two Cd II cations, three 1-ethyl-1H-imidazole ligands, and four Cl À anions. The two Cd II atoms have quite different coordination environments: one is octahedrally coordinated by four Cl atoms and two N atoms from two 1-ethyl-1H-imidazole ligands, and the second is in a severely distorted fivefold coordination by four Cl atoms and one N atom from a 1-ethyl-1H-imidazole ligand. Adjacent Cd II cations are interconnected alternately by pairs of chloride bridges, generating an infinite step-like chain along the a axis. One ethyl group of the 1-ethyl-1H-imidazole ligand is disordered over two sets of sites with a 0.668 (13):0.332 (13) site-occupancy ratio.

Comment
The title compound, [C 15 H 24 Cd 2 Cl 4 N 6 ], (I), was prepared from 1-ethyl-1H-imidazole and cadmium(II) chloride in N,N-dimethylformamide. The X-ray crystal structure of the title complex at 298 K (Fig. 1) shows a novel infinite one-dimensional coordination chain along the a axis (Fig. 2). There are two types of Cd atoms with different coordination environments: Cd(1) is coordinated by two 2-ethyl imidazole ligands and four bridging Cl atoms, and Cd(2) is in severely distorted pentahedral coordination by four bridging Cl atoms, and one 2-ethyl imidazole ligand.
In order to examine possible structure phase transitions of compound (I), we measured its temperature-dependent dielectric constant. Large dielectric anomalies usually indicate structural changes such as paraelectric-to-ferroelectric phase transitions. Unfortunately, the dielectric constant of compound (I) goes smoothly in the temperature range 93-273 K, suggesting the absence of distinct phase transitions (Ye et al., 2009;Zhang et al., 2009).

Experimental
A mixture of CdCl2 (2.27 g, 10 mmol) and 2-ethyl imidazole (1.82 g, 20 mmol) in water was stirred for several minutes at room temperature, to which was then added 10 ml N,N-dimethylformamide. Colourless block-shaped crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of the solution at room temperature over 2 weeks.

Refinement
Positional parameters of all H atoms except for H1A, H1B and H1C were calculated geometrically and the H atoms were set to ride the C atoms to which they are bonded, with U iso (H) = 1.2 U iso (C) and 1.5U iso (C) for methyl H atoms. The positional parameters of the H atoms (C1) were refined freely. And in the last stage of the refinement, they were restrained with the  catena-Poly [[bis(1-ethyl-1H-