CHROMOPHORE SELECTIVE RESONANCE RAMAN ENHANCEMENT IN COPPER(II) SQUARATE COMPLEXES WITH NITROGENOUS COUNTERLIGANDS

A resonance Raman investigation of the mixed ligand complexes Cu(bipy)Sq and Cu(phen)Sq (where Sq = squarate, bipy = 2,2'-bipyridine and phen = 1,10-phenanthroline) was undertaken. The results clearly indicate that the transitions observed at ca. 425 nm in the electronic spectra of such complexes can be assigned to a metal-oxocarbon charge transfer transition. In particular the carbonyl stretching mode is substantially enhanced, suggesting that the charge transfer is mainly located in that moiety of the oxocarbon. The drastic change observed in the enhancement pattern of the free oxocarbon can be ascribed to a significant reduction of its local symmetry in the mixed ligand complexes.