CORRELATION OF VIBRATIONAL AND ELECTRONIC-SPECTRA .1. VIBRONIC INTENSITY DISTRIBUTIONS AND LIGAND-FIELD STRENGTHS IN D-D-SPECTRA OF 5 PLANAR CUCL(2)X(2) CHROMOPHORES

A new approach is presented for the modeling of vibronic intensities of centrosymmetric transition metal ''d-d'' spectra. Relative contributions to intensity from different vibrational modes are determined by prior normal coordinate analysis of the vibrational spectra. The remaining variables in this cellular ligand-field (CLF) approach then relate to electronic, bonding factors alone as in our earlier model for acentric chromophores. The intensity distributions in five centric, planar chromophores, three with CuCl2N2 coordination and two with CuCl2O2, have been reproduced quantitatively by this new model. The vibronic intensity analyses are predicated upon CLF analysis of transition energies. The combination of energy and intensity analyses in these studies has removed earlier assignment ambiguities that could not be resolved by energy analyses and symmetry alone. An important feature of the CLF energy analyses of the CuCl2N2 species has been the establishment of large ligand-field strengths for ligations with heterocyclic imines, together with unusually large values of the associated ligand-field trace. These are ascribed to a significant ligand polarity within the complex, an interpretation which has wider implications for the understanding of CLF energy parameters in general. All CLF intensity parameter values appear to be consistent with this view and with those previously established from analyses of a wide range of acentric chromophores.