Trends in M(CN) isomerism: A computational study of monocyanides of the main-group third row atoms

Abstract

Ab initio calculations, using the G2 and G2(QCI) procedures, have been performed on the various isomers of the monocyanides of the atoms K, Ca, Ga, Ge, As, Se, and Br. In most instances, potential energy surfaces for the corresponding ions M(CN)⁺ have also been explored. At the levels of theory employed, π-complex minima are evident only for K(CN) and for Ca(CN)⁺: in almost all other instances, the global minimum is the linear cyanide geometry MCN. The barrier height to MCNMNC isomerization increases in a near-systematic fashion in going from left to right across the period; the energy difference E₀(MNC)-E₀(MCN) also shows a tendency to increase from M=K to M=Br. The ionization energies (IE) of both MCN and MNC increase from left to right, and in almost all cases IE(MCN)>IE(MNC). Results obtained in the present study are generally in good agreement with the (sometimes sparse) experimental record for these compounds.