Infrared multiphoton dissociation spectrum of CF_3Mn(CO)_3(NO)^-

Abstract

An infrared multiphoton dissociation spectrum of CF_3Mn(CO)(NO)^- has been obtained with Fourier transform ion cyclotron resonance spectroscopy combined with a line-tunable continuous wave CO_2 laser in the 925-1085 cm^(-1) wavelength range. The trifluoromethyl group in the anion shows two absorption maxima at 1045 and 980 cm^(-1). The peak at 1045 is assigned as a C-F stretch of A_1-type symmetry and the peak at 980 cm^(-1) is ascribed to a C-F stretch of E-type symmetry. It is quite interesting to observe that the symmetric C-F stretching mode changes little in frequency from 1063 cm^(-1) for CF_3Mn(CO)_5 to 1045 cm^(-1) for CF_3Mn(CO)_3(NO)^-, while the C-F stretching frequency of E-type symmetry decreases from 1043 cm^(-1) for the 18 e^- neutral precursor to 980 cm^(-1) for the 18 e^- anion. Comparison with the infrared multiphoton dissociation spectrum of CF_3Mn(CO)_4^- ion reveals that the degenerate C-F stretch of E-type symmetry increases from 945 cm^(-1) for the 17 e^- CF_3Mn(CO)_4^- to 980 cm^-1) for the 18 e^- CF_3Mn(CO)_3(NO)^-, whereas the symmetric C-F stretching bands overlap with each other within experimental uncertainties. Variations of the electron density and hybridization in the σ donor orbital of the CF_3 ligand due to the different d orbital splittings of the complexes may be responsible for the distinctive C-F stretching frequencies observed in CF_3Mn(CO)_5 (18 e^-), CF_3Mn(CO)_4^- (17 e^-), and CF_3Mn(CO)_3(NO)^- (18 e^-).