A theoretical survey of unsaturated or multiply bonded and divalent silicon compounds. Comparison with carbon analogs

Multiply bonded Si molecules, H2SiX (X = Be, BH, CH2, SiH2, NH, 0), HSiY (Y = B, CH, SiH, N), and SiZ (Z = 0, 02), along with their carbon analogues, have been investigated by ab initio methods. All structural parameters were optimized by use of the 3-21G basis set and the higher 3-21G(*) basis set for silicon. In addition, the isomeric substituted silylenes which result from 1,2-hydrogen shifts were also considered. In many cases, the substituted silylene structures were energetically favored. The effect of all first-row substituents on the singlet-triplet energy separation of divalent silicon molecules was assessed and compared with the corresponding carbenes.