Mixed ligand complexes of [CNCo(D2H2)L] (whereL=imidazoles, benzimidazoles, thiourea or hydroxylamine) were prepared by treating the [CNCo(D2H2)SCN] with ‘L’ in alcohol. Imidazoles and benzimidazoles bind to Co(III) through N3, thiourea throughS and hydroxylamine throughN of NH2. The analogous series of complexes enriched in13C and15N of the cyanide ligand have been used to locate the cyanide’s13C and15N NMR resonances and the cyanide stretching frequencies in the infrared spectra. As thetrans axial ligand is varied, an inverse dependence of the15N chemical shift on the13C chemical shift is observed. This data together with trends inδ15N,δ13C andν CN with the basicity of thetrans axial ligand are interpreted to indicate that the cobalt to cyanideπ bonding is important in these cyano (ligand) complexes.