CHARACTERIZATION OF ELECTRONIC STATES OF MIXED-LIGAND Ru(II) ORGANOMETALLIC COMPLEXES BY RESONANCE RAMAN SPECTROSCOPY

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1984

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Ohio State University

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The photochemical and photophysical properties of $Ru(bipy)_{3}^{++} [bipy = 2,2^{\prime}-bipyridine]$ and other $Ru(d^{6})$ complexes have been subjects of intense $investigation.^{1}$ These compounds show potential utility in photochemical energy conversion processes and are also of intrinsic interest. Woodruff and $coworkers,^{2}$ in an elegant interpretation of the resonance Raman spectra of the ground and lowest metal-to-ligand charge transfer (MLCT) excited electronic states, have demonstrated that the transferred electron in the MLCT state of $Ru(bipy)_{3}^{++}$ is localized on one bipy ligand rather than being delocalized among all three. That conclusion has been confirmed by other $workers.^{3}$ We have studied a series of $RuL_{2}M_{2}^{++}$ complexes, where L = bipy or 1,10-phenanthroline, M = acetylpyridine, benzoylpyridine, etc., by resonance Raman spectroscopy. In these cases two distinct MLCT transitions may arise, and the excited state resonance Raman spectra might serve to characterize which ligands are being ``reduced''. Raman scattering from the electronic ground states and from model ligand anions have been obtained under resonant cw illumination. Relatively high-power, tuned, pulsed-laser irradiation was used to both form and interrogate the MLCT states. The results will be discussed in terms of the relative MLCT and ligand field (LF) transition energies and the localized electron transfer model proposed for $Ru(bipy)_{3}$. $^{1}$ J. V. Caspar and T. J. Meyer, J. Am. Chem. Soc. 105, 5583 (1983), and references cited therein. $^{2}$ P. G. Bradley, N. Kress, B. A. Hornberger, R. F. Dallinger, and W. H. Woodruff, J. Am. Chem. Soc. 103, 7441 (1981). $^{3}$ W. K. Smothers and M. S. Wrighton, J. Am. Chem. Soc. 105, 1067 (1983); S. McClanahan, T. Hayes, and J. Kincaid, ibid., 4486 (1983).

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Author Institution: Department of Chemistry, Michigan State University

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