M. Murali et al., SYNTHESIS, SPECTRA AND ELECTROCHEMICAL-BEHAVIOR OF BIOMIMETIC COPPER(II) COMPLEXES WITH CUN5 AND CUN6 CHROMOPHORES, Inorganica Chimica Acta, 224(1-2), 1994, pp. 19-25
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.