ABOUT THE NATURE OF CARBON-NITROGEN TRIPLE BOND IN COMPLEXES OF NITRILES WITH STRONG LEWIS-ACIDS

Complexes of nitriles 1 - 7 with antimony(V) fluoride in cryogenic mat rices were studied by FT-IR spectroscopy. A large increase in C drop N stretching frequency induced by complexing with SbF5 is observed in a ll investigated nitriles. From the vibrational changes of the nitrile molecule skeleton, it was found that the polarity of the nitrile group is increased in the complex. The inductive effect caused by complexin g with SbF5 was studied by observing the changes of C-CN stretching an d CH3 or CH2 deformation vibrations. The qualitative similarity betwee n vibrational changes induced either by complexing or by ionization of nitriles is discussed. Current interpretations of the nitrile effect by rehybridization of nitrogen or by partially antibonding character o f the sigma orbital of CN bond are discussed on the basis of both the IR spectra and high level ab initio calculations.