Computational studies of the geometric and electronic structures of BF3+, AlF3+, CF32+ and SiF32+

The title cations have been studied computationally using spin-unrestricted B3LYP hybrid density functional theory and Møller–Plesset and coupled cluster ab initio approaches. In all cases bar B3LYP BF3+, the equilibrium geometry is found to be of planar C2v symmetry with one long and two short element–fluorine bonds. The ab initio calculations determine this geometry to be substantially more stable than the alternative D3h structure. Mulliken and atoms-in-molecules analyses support the assertion that the unique element–fluorine bond is appreciably weaker than the shorter E–F bonds, in agreement with our previous experimental conclusions.