Pentaaqua(1H-benzimidazole-5,6-dicarboxylato-κN 3)cobalt(II) pentahydrate

In the title mononuclear complex, [Co(C9H4N2O4)(H2O)5]·5H2O, the CoII atom exhibits a distorted octahedral geometry involving an N atom of a 1H-benzimidazole-5,6-dicarboxylate ligand and five water O atoms. A supramolecular network is generated through intermolecular O—H⋯O hydrogen-bonding interactions involving the coordinated and uncoordinated water molecules and the carboxyl O atoms of the organic ligand. An intermolecular N—H⋯O hydrogen bond is also observed.

In the title mononuclear complex, [Co(C 9 H 4 N 2 O 4 )(H 2 O) 5 ]Á-5H 2 O, the Co II atom exhibits a distorted octahedral geometry involving an N atom of a 1H-benzimidazole-5,6-dicarboxylate ligand and five water O atoms. A supramolecular network is generated through intermolecular O-HÁ Á ÁO hydrogenbonding interactions involving the coordinated and uncoordinated water molecules and the carboxyl O atoms of the organic ligand. An intermolecular N-HÁ Á ÁO hydrogen bond is also observed.

Comment
In the structural investigation of 1H-benzimidazole-5,6-dicarboxylate complexes, it has been found that the 1H-benzimidazole-5,6-dicarboxylic acid can function as a multidentate ligand (Gao et al., 2008;Lo et al., 2007;Yao et al., 2008), with versatile binding and coordination modes. In this paper, we report the crystal structure of the title compound, a new cobalt(II) complex obtained by the reaction of the 1H-benzimidazole-5,6-dicarboxylic acid and cobalt chloride in alkaline aqueous solution.
As illustrated in Figure 1, the cobalt(II) atom is six-coordinated by one N atom from a 1H-benzimidazole-5,6-dicarboxylate ligand and five O atoms from five water molecules, displaying a distorted octahedral geometry. The O1/O2/C7 and O3/O4/C8 carboxylate groups are tilted with respect to the plane of the benzimidazole ring system by 36.0 (3) and 68.1 (2)°, respectively. Intermolecular O-H···O hydrogen bonding interactions (Table 1) form a three-dimensional supramolecular network involving the coordinated and uncoordinated water molecules as donors and the carboxylate O atoms of the organic ligand as acceptors (Fig. 2). An intermolecular N-H···O hydrogen bond is also observed.

Experimental
A mixture of cobalt chloride (1 mmol), 1H-benzimidazole-5,6-dicarboxylic acid (1 mmol), NaOH (1.5 mmol) and H 2 O (12 ml) was placed in a 23 ml Teflon reactor, heated to 433 K for three days and then cooled to room temperature at a rate of 10 K h -1 . The crystals obtained were washed with water and dryed in air.

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

Special details
Geometry. All e.s. 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 Rfactors(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.