Resonance Raman spectra of d(6) metal-diimine complexes reflect changes inmetal-ligand interaction and character of electronic transition

This article reports the results of a comparative resonance Raman (rR) stud y of low-valent d(6) transition-metal a-diimine complexes. The oc-diimine l igand used is N,N'-diisopropyl-1,4-diaza-1,3-butadiene (Pr-i-DAB) which has a relatively simple structure and hence only a few vibrations. This simpli fies the assignment of the vibrational spectra of complexes of this ligand. With the help of DFT calculations of the frontier orbitals and vibrational frequencies of (model) complexes, the rR bands are assigned unambiguously. Their frequencies and intensities are discussed in terms of the electronic structures of the complexes. Comparison of the rR data demonstrates how th ese spectra can be used to establish changes in the metal-ligand interactio n and in the character of the charge transfer transitions of these complexe s. (C) 2001 Elsevier Science B.V. All rights reserved.