Abinitio molecular orbital calculations for SF4, SOF2, and SO2F2

Abinitio molecular orbital calculations are reported for SF4 (both C2v and C4v symmetries), SOF2, and SO2F2. Geometry searches were conducted using the STO-3G* basis set; the energies were recalculated at the predicted equilibrium structures also using STO-3G and 44-31G, and the latter basis set with the addition of five real d Gaussian orbitals on the sulfur atom. The predicted geometries agree well with experiment, although S=O bonds are consistently predicted too long by ∼0.03 Å, and the variation in S—F bond lengths among different environments is underestimated. The energy stabilization associated with the addition of d orbitals is generally consistent with our previous calculations, i.e. it is a constant amount per bond in hypervalent sulfur compounds in extended basis calculations. Replacement of F by OH is predicted to be more exothermic in SO2F2 than in SOF2, and the relevance of this prediction to estimated heats of formation for SOF2 and SO(OH)2 is discussed.