The nature of the bonding of the cyanide ligand to a metal atom and an organic group was examined through a study of the model systems CuCN, CuNC, CH3CN, and CH3NC. These particular molecules encompass extremes of bonding. Three properties of the wave functions are used to characterize the bond: (1) projection of the CN orbitale from the wave function of the complete system; (2) the dipole moment as a function of the distance between CH3 or Cu and CN; and (3) the energetic preference for the CN orientation. These measures show that the CuCN and CuNC bonding is dominantly ionic while the bonding for CH3CN and CH3NC is dominantly covalent. For the CH3 containing molecules, there is participation of the cyanide 2π* orbital in the bond; however, it is not involved in the ionic bond with Cu. In all cases considered, there is a large binding energy between CN and CH3 or Cu; CN can form strong bonds that are of either covalent or ionic character. © 1987 American Institute of Physics.