Vertical and adiabatical ionization potentials of MH−K+1 anions. Ab initio study of the structure and stability of hypervalent MHk+1 molecules

Vertical and adiabatic ionization potentials of the free MHk+1− anions, where M is a nontransition atom and k is the maximal formal valence of the atom M, have been studied by ab initio methods. Thermodynamic stabilities of the corresponding neutral hypervalent MHk+1 species have been calculated as well. LiH2−, BeH3−, MgH3−, BH4−, AlH4−, and SiH5− are very stable to loss of the extra electron and are stable geometrically at high symmetry structure, except for SiH5− which is not stable thermodynamically. LiH2, NaH2, BeH3, MgH3, and BH4 have minima at C2v (2B2) structures; however, only BH4 is thermodynamically stable to all possible dissociation asymptotes. The NaH2− anion is not adiabatically electronically stable.