A comparative ab initio study of the Si2C4, Si3C3, and Si4C2 clusters

Various structural possibilities for the Si2C4 and Si4C2 clusters are investigated by employing a basis set of triple-zeta plus polarization quality; electron correlation is generally accounted for by second-order Mo/ller–Plesset and, in certain instances, by higher-order perturbation (CASPT2) approaches. The building-up principle recently suggested from an analysis of Si3C3 clusters is found to be fully operative for Si2C4 and Si4C2 clusters. A comparison of the structure and stability of various geometrical arrangements in the series C6, Si2C4, Si3C3, Si4C2, and Si6 shows that linear and planar structures become rapidly less stable if carbons are replaced by silicons and that the three-dimensional bipyramidal forms become less favorable as soon as silicons are exchanged by carbons in the parent Si6 structure. The effects can be rationalized in qualitative terms based on differences in silicon and carbon bonding.