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

In the title mononuclear complex, [Ni(C9H4N2O4)(H2O)5]·5H2O, the NiII atom is six-coordinated by one N atom from a 1H-benzimidazole-5,6-dicarboxylate ligand and by five O atoms from five water molecules and displays a distorted octahedral geometry. Intermolecular O—H⋯O hydrogen-bonding interactions among the coordinated water molecules, solvent water molecules and carboxyl O atoms of the organic ligand and additional N—H⋯O hydrogen bonding lead to the formation of a three-dimensional supramolecular network.

In the title mononuclear complex, [Ni(C 9 H 4 N 2 O 4 )(H 2 O) 5 ]Á-5H 2 O, the Ni II atom is six-coordinated by one N atom from a 1H-benzimidazole-5,6-dicarboxylate ligand and by five O atoms from five water molecules and displays a distorted octahedral geometry. Intermolecular O-HÁ Á ÁO hydrogenbonding interactions among the coordinated water molecules, solvent water molecules and carboxyl O atoms of the organic ligand and additional N-HÁ Á ÁO hydrogen bonding lead to the formation of a three-dimensional supramolecular network.

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 (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 Ni complex obtained by the reaction of 1H-benzimidazole-5,6-dicarboxylic acid with nickel chloride in an alkaline aqueous solution.
As illustrated in Fig. 1, the Ni II atom exhibits a slightly distorted octahedral coordination sphere, defined by one N atom from the 1H-benzimidazole-5,6-dicarboxylate ligand and five coordinated water molecules. The five non-bonded solvent water molecules are located in cavities of the three-dimensional framework, allowing them to participate in various O-H···O hydrogen bonds (Table 1) with the coordinated water molecules, non-coordinated water molecules and carboxylate O atoms of the organic ligand. The hydrogen bonds are in the normal range (Table 1, Fig. 2).

Experimental
A mixture of nickel 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, which was 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 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). The water H atoms were located in a difference map, and were refined with a distance restraint of O-H = 0.84 Å; their U iso values were refined.   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.