Selected boron, aluminum, and gallium trihalide and trihydride anions

Ab initio methods with flexible orbital basis sets are used to examine the electron binding strengths of tri-fluorides, tri-chlorides, and tri-hydrides of B, Al, and Ga. The adiabatic electron affinities are found to increase with increasing atomic number of the central atom. For any given central atom M (M = B, Al, Ga), the adiabatic and vertical electronic stability for MCl3 is larger than that of the corresponding MF3. The tri-hydrides have quite different electron binding strengths than the corresponding tri-halides. BH3 has a very small EA (ca. 0.02 eV) and its anion is planar whereas the tri-halide anions and AlH3− and GaH3− are non-planar. AlH3 and GaH3 have considerably smaller EAs (ca. 0.3 eV) than the Al and Ga tri-halides (0.9-1.8 eV). In all, these anions provide species whose electron binding strengths span a considerable range (0.3-1.8 eV).

Energies of AlF3 and AlF3− as functions of the distortion away from planarity.60