An ab initio QCISD study of the periodic trends in structures and reactivities of the XH_5~- anions (X = Si, Ge, Sn, Pb)

摘要

QCISD, MP4 and QCISD(T) methods have been applied to compare structures and reactivities of the XH_5~- anions with X = Si, Ge, Sn, Pb. In particular, the exothermic XH_5~- -> XH_3~- + H_2 decompositions have been considered to occur via a stepwise mechanism. The energies required for the XH_5~- -> XH_4 + H~- dissociation step appeared to change irregularly with X, ranging from 14.5 to 31 kcal/mol. Energy decomposition analysis has been employed to clarify this periodic trend. The proton transfer step, XH_4 + H~- -> XH_3~- + H_2, has been predicted to be barrierless for X = Ge, Sn, Pb, and involving a tiny barrier of 0.2 kcal/mol for X = Si.