The design and synthesis of coordination polymers has attracted great interest in functional solid–state materials, owing to their excellent properties in magnetism, gas storage and electrooptic materials (Kumar et al., 2009; Farha et al., 2009; Zhou et al., 2006). Herein, compared with 1,4–benzenedicarboxylic acid, tetrachloroterephthalic acid can be used to construct materials which have different properties. Computational study suggests that 1,4–benzenedicarboxylic acid with chemical modification have better adsorption property in gas storage (Mulder et al., 2005; Zhang et al., 2007).

Single–crystal X–ray structural analysis reveals that the title cobalt(II) complex in crystal built from one–dimensional linear chains running along the crystallographic direction [1 1 0]. As shown in Fig. 1, the coordination geometry around the Co(II) atom is a slightly distorted octahedron with N₂O₄ binding set. In the octahedron unit, two O atoms from the tetrachloroterephthalate dianions ligands and two N atoms from the imidazole molecules form the equatorial plane and the axial position is occupied by O atoms from two water molecules. The Co—O bond lengths are 2.1653 (14)Å and 2.0865 (14)Å and agree well with the reported (Murugavel et al., 2002; Rogan et al., 2006). The Co—N bond length are 2.0896 (17)Å, which are comparable with the reported values in the similar complexes (Tong et al., 2002; Zhang & Lu, 2004). In addition, the imidazole and water molecules act as donors in N—H···O and O—H···O hydrogen bonds (Table 1). Adjacent one–dimensional chains are linked into a two–dimensional network arranged along the crystallographic b axis by classical N2—H2B···O2ⁱⁱⁱ and O3—H3A···O1ⁱ hydrogen bonds with the angles of 167° and 166°, respectivly. Symmetry codes: (i) -x+1, y, -z+1/2; (iii) -x+1/2, y+1/2, -z+1/2.

All the reagents and solvents employed were commercially available. Tetrachloroterephthalic acid was purified by recrystallization. In a 15 cm long tube, a solution of sodium tetrachloroterephthalate (0.0346 g, 0.1 mmol) and imidazol (0.0068 g, 0.1 mmol) in 5 mL methanol was carefully layered on top of a bilayer solution comprised of a solution of Co(NO₃)₂×6H₂O (0.0291 g, 0.10 mmol) in 5 mL water on the bottom and a buffer solvent of 6 mL ethyl acetate on the top at room temperature. Half a month later, pink block–shaped crystals were obtained, washed with water, and dried on air (0.0618 g, yield: 58% based on Co). Elemental analysis(%) calcd. for C₁₄H₁₂Cl₄CoN₄O₆: C, 31.52; H, 2.25; N, 10.51. Found: C, 31.37; H, 2.24; N, 10.47%.

All the other H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C—H, O—H and N—H distances of 0.93Å, 0.85Å and 0.86Å with U_iso(H) = 1.2(1.5)U_eq(C, O, N). All C—Cl bond lengths were restrained to 1.728–1.729 (2)Å.

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+1/2, −y+1/2, −z.

Symmetry codes: (i) −x+1, −y+1, −z+1; (iii) −x+1, y, −z+1/2; (iv) −x+1/2, y+1/2, −z+1/2.