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

Ab initio calculations, using the G2 and G2(QCI) procedures, have been perf ormed 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 corr esponding ions M(CN)(+) have also been explored. At the levels of theory em ployed, pi-complex minima are evident only for K(CN) and for Ca(CN)(+): in almost all other instances, the global minimum is the linear cyanide geomet ry MCN. The barrier height to MCN reversible arrow MNC isomerization increa ses in a near-systematic fashion in going from left to right across the per iod; the energy difference E-0(MNC)-E-0(MCN) also shows a tendency to incre ase 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). Res ults obtained in the present study are generally in good agreement with the (sometimes sparse) experimental record for these compounds.