Quantum Chemical Calculation of Raman Intensities for Large Molecules: The Photoisomerization of [{Fe‘S4’(PR3)}2(N2H2)] (‘S4’2− = 1,2-bis(2-Mercaptophenylthio)-Ethane(2−))

Abstract

Abstract Since Raman spectra of isolated large molecules are hardly accessible by present day quantum chemical methods, we demonstrate how Raman intensities for selected vibrational normal modes can be calculated by extension of a semi-numerical, very flexible approach to the calculation of vibrational spectra [see J. Neugebauer et al., J. Comp. Chem. 23 (2002) 895–910]. The methodology is applied to a Ci -symmetric dinuclear diazene iron–sulfur complex with relevance to the biological nitrogen fixation problem. The accuracy of the vibrational spectra allows us to use the spectra for structure determination and assignment of bands to isomeric structures, which were conjectured to be generated by a photoisomerization process. We can in turn support the photoisomerization hypothesis.