Photoelectron imaging and theoretical studies of group 11 cyanides MCN (M = Cu, Ag, Au)

Photodetachment of group 11 cyanide anions MCN(-) (M = Cu, Ag, Au) has been investigated using photoelectron velocity-map imaging. The electron affinities (EAs) of CuCN (1.468(26)) and AgCN (1.602(22)) are larger, while that of AuCN (2.066(8)) is smaller than those of the free atoms. This intriguing observation was confirmed by theoretical studies and was assigned to the transition between ionic and covalent bond properties. The harmonic frequencies of the extended vibrational progressions in the M-C stretching mode are 460(50), 385(27), and 502(10) cm(-1), respectively, which suggests a stronger bond for Au-CN than for Ag-CN. Electronic structure analysis and model calculations suggest that all M-C bonds in group 11 cyanides are best described as single bonds. A model has been proposed to explain how the relativistic effects influence the Au-C bond strength in AuCN.