SYNTHESIS, SPECTRA AND ELECTROCHEMICAL-BEHAVIOR OF BIOMIMETIC COPPER(II) COMPLEXES WITH CUN5 AND CUN6 CHROMOPHORES

The Cu(ClO4)2 complexes of the two pentadentate ligands, '-tris(benzim idazol-2'-ylmethyl)-1,2-ethanediamine and its 6'-methyl derivative and four sexadentate ligands, rakis(benzimidazol-2'-ylmethyl)-1,2-ethaned iamine, s(benzimidazol-2'-ylmethyl)-1,2-cyclohexanediamine and their 6 '-methyl derivatives have been isolated and studied. They are of the t ype CuL(ClO4)2.nH2O where n = 0, 1. All the complexes exhibit two liga nd field bands and the nuBAR(max) and epsilon values are lower and hig her, respectively, than the range known for CuN4 chromophores. Compare d to the latter they also have high g(parallel), low A(parallel) and h igh g(parallel)/A(parallel) values. These spectral data are consistent with an appreciable displacement and/or tetrahedral twist of copper f rom the N4 square plane of the complexes. The anchoring of a bulky ben zimidazole moiety to ,N'-bis(benzimidazol-2-ylmethyl)-1,2-ethanediamin e to incorporate a N-donor axial to the planar CuN4 chromophore decrea ses CFSE and enhances the Cu(II)-Cu(I) redox potential. However, addit ion of two benzimidazole nitrogens to the N4 ligand to obtain a CuN6 c hromophore, depresses the redox potential. Further, the fusion of a cy clohexyl ring into the above CuN6 chromophore dramatically leads to el evation in E1/2 with increase in reversibility. The introduction of a methyl group in the aromatic ring, far away from the redox centre, dep resses E1/2.