Aqua(1H-benzimidazole-κN 3)(pyridine-2,6-dicarboxylato-κ3 O 2,N,O 6)copper(II) 0.75-hydrate

The title complex, [Cu(C7H3NO4)(C7H6N2)(H2O)]·0.75H2O, consists of discrete monomeric units. The CuII atom is coordinated by two carboxylate O atoms and the N atom from a dipicolinate unit and by an N atom from a benzimidazole ligand. The distorted square-pyramidal geometry is completed by a longer axial bond to the O atom of a water molecule. The molecular structure and packing are stabilized by classical O—H⋯O and N—H⋯O hydrogen bonds, also including a disordered crystal water molecule.

The title complex, [Cu(C 7 H 3 NO 4 )(C 7 H 6 N 2 )(H 2 O)]Á0.75H 2 O, consists of discrete monomeric units. The Cu II atom is coordinated by two carboxylate O atoms and the N atom from a dipicolinate unit and by an N atom from a benzimidazole ligand. The distorted square-pyramidal geometry is completed by a longer axial bond to the O atom of a water molecule. The molecular structure and packing are stabilized by classical O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds, also including a disordered crystal water molecule.

Related literature
For related structures of dipicolinate complexes, see: How et al. (1991).

Comment
The dipicolinic acid (pyridine-2,6-dicarboxylic acid) has important biological functions in the organism and commonly coordinate to transition metals by either carboxylate bridges between metal centers, to form polymeric or dimeric complexes or tridentate (O, N, O') chelation to one metal ion. Some Cu(II) dipicolinate complexes with imidazole had been reported (How et al., 1991). Here, we report here the crystal structure of the title compound.
The molecular structure of the title compound, is illustrated in Fig. 1. All the bond lengths and angles are in the normal range (How et al., 1991). The overall molecular structure of title complex, has only independent Cu(II) ion, is five-coordinated by one N and two O atoms from a dipicolinate dianion ligand, one N atom from a benzimidazole molecule and one O atom of a water molecule. In molecular structure, each Cu(II) center exhibits a slightly distorted square pyramidal environment. The intermolecular hydrogen bonds play an important role in the crystal packing and the stability of the complex (Table 1).

Experimental
Copper(II) hydroxide (98 mg, 1 mmol) was treated with an aqueous solution (10 mL) of dipicoline acid (334 mg, 2 mmol) in a steam bath until the solid disappeared. The solution was then filtered and diluted to approximately 40 mL with water.
An methanol solution (10 mL) of benzimidazole (472 mg, 4 mmol) is then added to above solution. The resultant clear-blue solution is warmed on a steam bath for 1 h. The volume is kept constant by periodic addition of water. Then the solution is filtered and allowed to stand at room temperature. Blue crystals suitable for X-ray single diffraction were obtained after 20 days.

Refinement
All H atoms were positioned geometrically an refined using a riding model with C-H = 0.93Å and U iso (H) = 1.2U eq (C) for aromatic H, O-H = 0.85Å and U iso (H) = 1.5U eq (O) for the OH group and N-H = 0.86Å and U iso (H) = 1.2U eq (N) for the NH group. Fig. 1. The molecular structure of the title compound, with the atom numbering scheme. The displacement ellipsoids are drawn at 30% probability level. h atoms are presented as a small spheres of arbitrary radius. Symmetry codes: (i) −x, −y, −z+2; (ii) −x, −y+1, −z+2; (iii) −x+1, −y, −z+2.