Solvent-dependent resonance raman spectra of high-valent Oxomolybdenum(V) tris[3,5-bis(trifluoromethyl)phenyl]corrolate

UV-visible, infrared (IR), and resonance Raman (RR) spectra were measured and analyzed for a high-valent molybdenum(V)-oxo complex of 5,10,15-tris[3,5-bis(trifluoromethyl)phenyl]corrole at room temperature. The strength of the metal-oxo bond in was found to be strongly solvent-dependent. Solid-state IR and RR spectra of exhibited the (MoO)-O-V stretching vibration at nu((MoO)-O-V) = 969 cm(-1). It shifted up by 6 cm(-1) to 975 cm(-1) in n-hexane and then gradually shifted to lower frequencies in more polar solvents, down to 960 cm(-1) in dimethyl sulfoxide. The results imply that stronger acceptor solvents weaken the (MoO)-O-V bond. The 45-cm(-1) frequency downshifts displayed by containing an O-18 label in the molybdenum(V)-oxo unit confirmed the assignments for the observed IR and RR nu((MoO)-O-V) bands. The solvent-induced frequency shift for the nu((MoO)-O-V) RR band, measured in a series of 25 organic solvents ranging from n-hexane (AN = 0.0) to N-methylformamide (AN = 32.1), did not decrease in direct proportion to Gutmann's solvent acceptor numbers (ANs). However, a good linear correlation of the nu((MoO)-O-V) frequency was found against an empirical "solvent polarity" scale (A + B) of Swain et al. J. Am. Chem. Soc. 1983, 105, 502-513. A molecular association was observed between chloroform and oxomolybdenum(V) corrole through MoO center dot center dot center dot H/CCl3 hydrogen-bonding interactions. This association manifested itself as a shift of the nu((MoO)-O-V) RR band of in CDCl3 to a higher frequency compared to that in CHCl3.