ASSIGNMENT OF THE ELECTRONIC-SPECTRA OF TRIS(MU-HALO)BIS(TRIAMMINERUTHENIUM)(2+) IONS USING RESONANCE RAMAN-SPECTROSCOPY

Several assignments have been made previously for the strong visible absorption in the electronic spectra of the tris(M-halo)bis-(triammineruthenium)(2+) ions for the halogens X = Cl, Br. The assignments derived from MCD measurements disagree with those derived from resonance Raman (RR) spectroscopic studies. In the present work, RR spectra in the region of the metal-ligand vibrations have been recorded for exciting wavelengths that cover most of the visible region. In addition, the depolarization ratios of the resonance-enhanced Raman bands have been recorded with greater accuracy and over a wide range of exciting wavelengths. These measurements indicate that intensity enhancement of the Ru—X bands in the RR spectra is due to a z-polarized transition that has been assigned as σ → σ* (in accord with the previous RR study). The relative enhancements of the Ru-X and Ru-N band intensities vary over the range of exciting wavelengths, and it is proposed that the transition σ* →π* contributes to the intensity of the Ru—N band at higher excitation energies. Accordingly, this transition can be assigned in the spectra of the two complexes. From the assignments of the transitions σ ∙ σ* and σ* →π* a reasonable set of assignments for the remaining bands in the electronic spectra has been proposed. © 1990, American Chemical Society. All rights reserved.