Vibrational spectra and force constants of the hexacarbonyls of chromium, molybdenum and tungsten

Abstract

Abstract The infrared absorption spectra of the hexacarbonyls of Cr, Mo, and W have been observed in the gaseous and solid states. Eleven of the thirteen fundamental frequencies of each have been assigned. Force constants were calculated using a resonance interaction potential function. The order of metal carbon force constants is F WC > F CrC > F MoC . For these three hexacarbonyls it is found that a higher metal-carbon force constant is accompanied by a lower CO force constant, indicating a decrease in metal—ligand π bonding in the same order as the metal-carbon force constants. The various calculated interaction constants are discussed. They all have reasonable values except the non-coplanar MCO, MCO bending interaction constants, which are unexpectedly large. The results of this work support the use of the resonance interaction valence force field for molecules of this sort.