ABINITIO MO STUDIES ON SI2H6,SIH3GEH3, AND GE2H6 RADICAL-ANIONS AS PROTOTYPES OF POLYMER ANIONS WITH SILICON AND GERMANIUM BACKBONES

Disilane, silylgermane, and digermane radical anions have been studied by ab initio molecular orbital theory, using the unified level of basis set as prototypes of polymer anions with Si and Ge backbones. These prototype anions have the same kind of minimum geometry (C2h or C2h-like symmetry) with an unpaired electron occupying the Si-Si, Si-Ge, or Ge-Ge sigma* antibonding orbital with a large Si or Ge s diffuse orbital contribution. Little Si 3d or Ge 4d orbital participation is found for these anions. All these anions can exist as kinetically bound anions with positive first vertical ionization potential values. The stability of an unpaired electron is in the order Si2H6- < SiH3GeH3- < Ge2H6-. The origin of this stability difference is also discussed. These results suggest that polymer anions with Si and Ge backbones have the same kind of molecular and electronic structures with no dpi-dpi conjugation and that their stability is in the order polysilane anion < Si-Ge copolymer anion < polygermane anion.