Magnetic circular dichroism studies of the charge-transfer transitions in tetrachloro and tetrabromocomplexes of transition metal ions

Abstract

We report on a detailed study of the temperature dependence of the magnetic circular dichroism spectra of the tetrabromo and tetrachloro-complexes of Cu(II), Fe(III) and Co(II) through their charge transfer absorption bands. All M.C.D. and absorption spectra were measured as far as about 44 000 cm^-1 on polymer films obtained by evaporating an acetonitrile solution of cellulose diacetate doped with the metal complex. This investigation considerably extends our previous room temperature M.C.D. work and leads to more reliable and detailed spectroscopic assignments than absorption spectra alone. A moment analysis of the FeBr₄ ^- spectra further indicates that non-cubic metal-halogen stretching modes play an important role in the band broadening mechanism. Our data also confirm that the highest occupied orbitals of mainly ligand character occur throughout the series in the order 1e<3t ₂<t ₁.