Resonance raman spectra of some ferric and cupric thiolate complexes

Abstract

Resonance Raman (RR) spectra of intensely absorbing (at ∼600 nm) transient ferric thiolate species obtained by mixing iron(III) salts with l-cysteine, d-penicillamine, N-acetyl- d-penicillamine, and α-mercaptopropionic acid were measured between 250 and 500 cm −1. RR spectra of a red ferric d-penicillamine complex showing band maxima at 500 and 550 nm and of oxidized spinach ferredoxin are also reported. Vibrational bands in the low-frequency region are associated with ν(FeS) and ν(FeO) modes, resonance-enhanced with excitation into an iron-sulfur charge transfer electronic transition. Iron-ligand bond strength and possible structure-stability correlations are suggested. In addition, the RR spectrum of the violet Cu IIN 2S 2 core-containing copper d-penicillamine cluster complex was obtained. Comparisons with RR spectra of “blue” copper proteins and reinterpretation of the latter spectra are made. Use of Franck-Condon factors in interpreting resonance-enhancement of particular modes of vibration is discussed with regard to metal-ligand vibrations and charge transfer electronic transitions.