Solvent effects on the infrared spectra of chromium, Molybdenum and tungsten hexacarbonyls.

Abstract

The effects of solvent on the infrared spectra of chromium, molybdenum and tungsten hexacarbonyls have been investigated in the 70–2100 cm. 1− regions for twelve solvents. for all three hexacarbonyls, the CO stretching vibration is lower in solution than in the vapour state,ν vap-ν soln ranging from 7.6 to 21.5 for chromium, 11.8 to 23.7 for molybdenum and 9.3 to 24.3 cm. 1− for tungsten. These frequency shifts are discussed in terms of the theory of Drickamer and coworkers. The MCO bending vibrations are almost solvent independent, the average values of ν vap-ν soln being +4.6±1.8, —2.9±3.2 and —1.0±1.7 for M = Cr, Mo and W respectively. Similarly the MC stretching vibrations are almost solvent independent (except in the case of chromium), the average values of ν vap-ν soln being —4.5±2.9, +5.0±1.2 and +6.0±1.4 for M = Cr, Mo and W respectively. Although the CMC bending vibrations have been located for nujol mulls of the metal carbonyls, the instrument proved to be insufficiently sensitive to locate these bands accurately in solution.