INFRARED MULTIPHOTON DISSOCIATION SPECTRUM OF CF3MN(CO)3(NO)-

An infrared multiphoton dissociation spectrum of CF3Mn(CO)3(NO)- has been obtained with Fourier transform ion cyclotron resonance spectroscopy combined with a line-tunable continuous wave CO2 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 A1-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 CF3Mn(CO)5 to 1045 cm-1 for CF3Mn(CO)3(NO)-, while the C-F stretching frequency of E-type symmetry decreases from 1043 cm-1 for the18 e- neutral precursor to 980 cm-1 for the 18 e- anion. Comparison with the infrared multiphoton dissociation spectrum of CF3Mn(CO)4- ion reveals that the degenerate C-F stretch of E-type symmetry increases from 945 cm-1 for the 17 e- CF3Mn(CO)4- to 980 cm-1 for the 18 e- CF3Mn(CO)3(NO)-, where as the symmetric C-F stretching bands overlap with each other within experimental uncertainties. Variations of the electron densityandhybridization in the donor orbital of the CF3 ligand due to the different d orbital splittings of the complexes may be responsible for the distinctive C-F stretching frequencies observedinCF3Mn(CO)5 (18 e-), CF3Mn(CO)4-(17 e-), and CF3Mn(CO)3(NO)- (18 e-). © 1990, American Chemical Society. All rights reserved.