Ab initio calculations on the bonding properties of isonitrile and nitrile ligands

Ab initio calculations have been performed on CNCH3 and NCCH3 to evaluate the change in σ-donor and π-acceptor character as a function of molecular geometry. For CNCH3, it is shown that as the CNCH3 angle decreases, the π-acceptor character increases markedly, while the π-donor character remains essentially constant. For NCCH3, calculations indicate a potential π-donor character for the ligand; a similar decrease in the NCCH3 angle results in a decrease in π-acceptor capability. The results are discussed in the light of relevant structural, spectroscopic, and kinetic literature data.