Bis[2-(1H-benzimidazol-2-yl)benzoato]copper(II) dihydrate

In the title compound, [Cu(C14H9N2O2)2]·2H2O, the Cu(II) ion lies on a centre of symmetry and is four-coordinated by two N atoms and two O atoms from two 2-(1H-benzimidazol-2-yl)benzoate ligands in a square-planar environment. The benzimidazol and benzyl rings form a dihedral angle of 42.8 (5)°. The molecule contains two H-bonded carboxyl O acceptors and two H-bonded N—H donors in the benzimidazol groups, which interact with two symmetry-related uncoordinated water molecules so that neighboring molecular units are linked by (O—H)water⋯Ocarboxyl hydrogen bonds with an R 2 4(8) graph-set motif, generating a helical chain in the a-axis direction. These chains are, in turn, interconnected by (N—H)benzimidazol⋯Owater hydrogen bonds, forming a three-dimensional supramolecular network.

Herein, the condensation of 1,2-diaminobenzene with 2-formylbenzoic acid in the presence of copper acetate lead to a new structure, Cu(C 14 H 9 N 2 O 2 ) 2 .2H 2 O, the title compound herein reported .
As depicted in Fig. 1, the Cu II ion lies on a centre of symmetry and is four-coordinated by two N atoms and two O atoms from two 2-(1H-Benzimidazol-2-yl)benzoate ligands in a square planar environment. The planar benzimidazol and benzyl rings form a dihedral angle of 42.8 (5)°. The molecule contains two H-bonded carboxyl O acceptors and two H-bonded N-H donors in the benzimidazol groups which interact with two symmetry-related lattice water molecules (symmetry code: 2 -X, 2 -Y, 2 -Z) in a way that neighboring molecular units are linked by (O-H) water ···O carbox hydrogen bonding with an R 2 4 (8) graph set motif (Bernstein et al., 1995) to generate a helical chain in the a-axis direction. These chains are in turn interconnected by (N-H) benzimidazol ···O water hydrogen bonds and extend to form a three-dimensional supramolecular network (table 1; Fig. 2)

Refinement
All water H atoms were tentatively located in difference density Fourier maps and were refined with O-H distance restraints of 0.83 (1) Å and with U iso (H) = 1.5 U eq (O). In the last stage of refinement, they were treated as riding on their parent O atoms. All H atoms attached to C and N atoms were fixed geometrically and treated as riding with C-H = 0.93 Å and N-H = 0.86 Å, and U iso (H) = 1.2U eq (C) and U iso (H) = 1.5U eq (N).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.