Synthesis, structures and properties of copper(II) and zinc(II) complexes with 1,2-bis(benzimidazol-2-yl)ethane ligands

1,2-Bis(benzimidazol-2-yl)ethane (bbe) and its transition metal complexes, [Cu(bbe)Cl-2]center dot DMF (1) and [Zn(bbe)Cl-2](2) (2), have been synthesized and characterized by elemental analysis, UV-Vis and IR spectra. X-ray crystal structure analysis revealed that both complexes have four-coordinate, distorted tetrahedral geometries. Complex 2 has two crystallographically independent but chemically identical Zn(bbe)Cl-2 units. The cyclic voltammogram of complex 1 shows an irreversible Cu2+/Cu+ couple. In vitro antioxidant tests showed that complex 1 has significant antioxidant activity against superoxide. Photoluminescence investigations showed that complex 2 exhibits light blue (441 nm) photoluminescence. Compared with the free bbe proligand, a redshift of 16 nm was observed for complex 2, which may be attributed to pi*-pi transitions.