Infrared Spectra of Some Transition-metal (Fe, Co, Ru, and Ir) Nitrosyl (14NO and 15NO) Complexes

Twelve 15NO-complexes of iron, cobalt, ruthenium, and iridium were prepared. The correlations of the isotopic shifts of their IR spectra with a metal–(NO) bond angle were investigated. For several nitrosyl complexes, the absorption bands due to the skeletal vibrations between the metal and the NO group were clearly assigned. Of the two absorption bands in the region 250–650 cm−1, the absorption band with a smaller isotopic shift could be assigned to the metal–(NO) stretching vibration and that with a larger isotopic shift to the metal–(NO) bending vibration.