Separation of mass effects from electronic effects in the vibrational spectra of metal complexes

Abstract

An analysis has been made of the effects of off-diagonal elements of the force constant and G matrices on the vibrational frequencies of octahedral halides. It has been shown that bend–stretch interaction can reasonably be neglected, and hence for the molecules MX₆ the i.r. and Raman spectra are sufficient to determine the three stretching force constants necessary to determine the complete harmonic force field. This force field is then used to predict a first approximation to the M–X stretching frequencies of the series MX_nY_{6 –n}. Finally the vibrational spectrum of WF₅Cl is analysed to give possible sets of force constants and from these it is possible to conclude that replacement of F by Cl strengthens the trans-W–F bond and weakens the cis-W–F bonds.