Raman Spectra and Intermolecular Vibrational Coupling Behaviour of Binary Mixed Crystals of dppmMCO4 Complexes M=Cr, Mo, W

Abstract

The Raman spectra of binary mixed crystals of (dppm)M(CO)4 complexes [dppm=bis(diphenyl-phosphino)methane, M=Cr, Mo, W] in the ν(CO) region are interpreted in terms of one-mode and two-mode behaviours, resulting from the presence and absence of intermolecular vibrational coupling in the unit cell, respectively. The behaviour of the spectral features in the mixed crystals is successfully correlated with the occurrence of factor group splitting in the individual spectra of the pure compounds. An unexpected wavenumber shift effect depending on crystal composition was detected. An explanation is proposed based on the breakdown of translational symmetry in mixed crystals and consequent invalidity of the k=0 rule.