Encapsulation of nickel(II) and copper(II) by a tetraazamacrocyclic ligand

A tetraazamacrocyclic ligand, L, containing six non-equivalent benzene rings, derived from the condensation of benzil with 1,2- diaminobenzene, has been isolated and its complexes [MLCl2] (M = Ni2+ and Cu2+) prepared and characterized by elemental analysis, i.r., u.v.–vis., e.p.r. spectral studies, magnetic moments, redox potentials and conductivity measurements. The complexes have axially elongated octahedral geometries with two axial chlorines, and adopt the trans-configuration. These studies also indicate the covalent nature and the high-spin octahedral structure for these complexes. A cyclic voltammetric investigation reveals that the complexes exhibit a single one-electron redox couple, as anticipated for a copper(II) complex (Cu2+/Cu+) and a single two-electron redox couple for a nickel(II) complex (Ni2+/Ni0). The electrochemical processes are considered quasi-reversible. Antimicrobial activities of the ligand and the complexes have been tested against Bacillus megaterium and Candida tropicallis.