Molecular properties and potential energy surfaces of the cyanides of the groups 1 and 11 metal atoms.

Ab initio calculations on the metal (groups 1 and 11) cyanide complexes show two stable configurations for the ground state geometry, a linear cyanide (MCN) and a triangular (MNC) form with an obtuse M-N-C angle. Lithium complex may exist in a linear isocyanide (MNC) form, but it cannot be differentiated from the triangular configuration because of the flatness of the potential energy surface connecting the two isomers. The metal atom and cyano radical are bonded through a strongly ionic configuration (M+CN-) in both geometrical forms. The MNC triangular form is a very floppy structure having one low frequency for the bending mode, whereas the MCN linear form is more rigid. The CN complexes of the alkali atoms have a triangular geometry as the lowest energy conformer, while the noble metal atoms prefer the linear cyanide one. The relative stability of the two isomers, dipole moments, and effective charges are reported in this paper. The essential aspects of the potential energy surfaces for the ground and the first excited states exhibiting a closely avoided crossing are also explained.