Tetraaquabis[4-(1H-imidazol-1-yl-κN 3)benzoato]cobalt(II)

In the title compound, [Co(C10H7N2O2)2(H2O)4], the CoII atom lies on an inversion centre and displays a slightly distorted octahedral geometry. The coordination sphere is defined by two mutually trans N atoms from two 4-(imidazol-1-yl)benzoate ligands and the O atoms from four water molecules. The crystal structure is stabilized by O—H⋯O hydrogen bonds.

In the title compound, [Co(C 10 H 7 N 2 O 2 ) 2 (H 2 O) 4 ], the Co II atom lies on an inversion centre and displays a slightly distorted octahedral geometry. The coordination sphere is defined by two mutually trans N atoms from two 4-(imidazol-1-yl)benzoate ligands and the O atoms from four water molecules. The crystal structure is stabilized by O-HÁ Á ÁO hydrogen bonds.

Related literature
For our previous work on imidazole derivatives as ligands, see:  ;Fan et al. (2010); .
Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97. During the past decade, considerable efforts have been devoted to design and construct new metal-organic frameworks due to their intriguing structural diversity and potential application in many areas. In recent years, our research group has shown great interest in the design and synthesis of interesting metal-organic complexes with imidazole derivatives such as 2-propyl-imidazole-4,5-dicarboxylic acid (Fan et al., 2010;Li et al., 2010) and 2-ethyl-1H-imidazole-4,5-dicarboxylic acid . In this paper, we report the synthesis and structure of a new Co II complex, As illustrated in Fig. 1, the title compound, consists of a Co II cation, two deprotonated 4-(imidazol-1-yl)benzoic acid ligands and four coordinated water molecules. Each six coordinate Co II ion, lies on an inversion center with the N atoms of the 4-(imidazol-1-yl)benzoic acid ligands mutually trans and the four water molecules in an equatorial plane. The Co-N distance is 2.1238 (15) Å and Co-O distances are 2.0643 (13) Å and 2.1287 (14) Å, respectively. It is interesting to note that in this molecule, the 4-(imidazol-1-yl)benzoic acid ligands coordinate to Co(II) via a nitrogen atom of the imidazole residue unlike several other complexes of dicarboxylic acid derivatives we have reported previously, which coordinate to metal atoms via the carboxylate group (Fan et al., 2010;Li et al., 2010;. In the crystal structure, molecules form a three-dimensional network through an extensive series of intermolecular O-H···O hydrogen bonds.

Experimental
A mixture of Co(NO 3 ) 2 .6H 2 O (0.5 mmol, 0.15 g) and 4-(imidazol-1-yl)benzoic acid (1 mmol, 0.19 g) in 12 ml of H 2 O was sealed in an autoclave equipped with a Teflon liner (20 ml) and then heated to 433 K for 4 days. After gradual cooling to room temperature, red crystals were obtained and collected by filtration with a yield of 31% based on Co.

Refinement
Carbon and nitrogen bound H atoms were placed at calculated positions and were treated as riding on the parent C or N atoms with C-H = 0.93 Å, N-H = 0.86 Å, and with U iso (H) = 1.2 U eq (C, N). H atoms of the water molecules were located in a difference Fourier map and refined as riding with an O-H distance restraint of 0.84 (1) Å and with U iso (H) = 1.5 U eq . The H···H distances within the water molecules were also restrained to 1.39 (1) Å.

Computing details
Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).  Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.