Two mononuclear octahedral complexes with benzimidazole-2-carboxylate: supramolecular networks constructed by hydrogen bonds.

The title compounds, trans-bis(1H-benzimidazole-2-carboxylato-κ(2)N(3),O)bis(ethanol-κO)cadmium(II), [Cd(C(8)H(5)N(2)O(2))(2)(C(2)H(6)O)(2)], (I), and trans-bis(1H-benzimidazole-κN(3))bis(1H-benzimidazole-2-carboxylato-κ(2)N(3),O)nickel(II), [Ni(C(8)H(5)N(2)O(2))(2)(C(7)H(6)N(2))(2)], (II), are hydrogen-bonded supramolecular complexes. In (I), the Cd(II) ion is six-coordinated by two O atoms from two ethanol molecules, and by two O and two N atoms from two bidentate benzimidazole-2-carboxylate (HBIC) ligands, giving a distorted octahedral geometry. The combination of O-H···O and N-H···O hydrogen bonds results in two-dimensional layers parallel to the ab plane. In (II), the six-coordinated Ni(II) atom, which lies on an inversion centre, shows a similar distorted octahedral geometry to the Cd(II) ion in (I); two benzimidazole molecules occupy the axial sites and the equatorial plane contains two chelating HBIC ligands. Pairs of N-H···O hydrogen bonds between pairs of HBIC anions connect adjacent Ni(II) coordination units to form a one-dimensional chain parallel to the a axis. Moreover, these one-dimensional chains are further linked via N-H···O hydrogen bonds between HBIC anions and benzimidazole molecules to generate a three-dimensional supramolecular framework. The two compounds show quite different supramolecular networks, which may be explained by the fact that different co-ligands occupy the axial sites in the coordination units.