Contrasting Stabilities of Classical and Bridged Pyramidal Si3H3X Molecules (X = BH-, CH, N, NH+, NO, SiH, P, PH+, and PO)

Abstract

Trigonal-pyramidal Si3H3X systems have been studied at HF/6-31G*, MP2(FC)/6-31G*, and Becke3LYP/6-31G* levels. The classical trigonal-pyramidal structure (5) is a higher order stationary point for X = BH-, CH, NO, SiH, P, PH+, and PO, whereas it is a minima for X = N and NH+, at the MP2(FC)/6-31G* level. An alternative pyramidal structure (6, C3v) with three SiHSi 3c−2e bonds is minima, lower in energy than 5 by 47.7 (X = BH-), 39.1 (X = CH), 31.7 (X = N), 25.0 (X = NH+), 20.6 (X = SiH), 20.7 (X = P), 16.1 (X = PH+), and 18.2 (X = PO) kcal/mol. Isolobal analogy connects 6 with various triply hydrogen bridged pyramidal structures in organometallics.