Structural and electrochemical studies of dicopper complexes of a binucleating ligand involving sulfides and benzimidazoles

The reaction of malondialdehyde with mercaptoacetic acid furnishes a tetraacid which upon condensation with 1,2-diaminobenzene gives the tetrathioethertetrabenzimidazole binucleating ligand (L). One copper(I) and three copper(II) complexes of this ligand have been isolated. The latter are not stable in solution where they are reduced by the solvent or the ligand itself. An investigation of the structures of the compounds by EXAFS and XANES techniques has shown that in the copper(I) complex the metal is in an N2S environment of T-shaped geometry. The copper(II) derivatives are square pyramidal and there is no sulfur atom in the tetragonal plane. This situation is in agreement with the absence of magnetic interaction between the two copper(II) ions in the oxidized compounds. All complexes exchange electrons at high potentials of the Cu(I)/Cu(II) couple in the range 0.2-0.6 V-sce.