Chemical bonding in oxofluorides of hypercoordinate sulfur

Modern valence bond theory, in its spin-coupled form, is used to investigate the bonding in sulfuryl fluoride, SO 2 F 2 , and in the thionyl fluorides, SOF 2 and SOF 4 . Analogous calculations are also carried out for SO 2 , SO 3 and SF 4 , to enable various comparisons to be made. We find that the sulfur atoms in these systems utilize all six valence electrons in two-centre two-electron polar covalent bonds and in angularly split lone-pair-like orbitals. Although based on just a single orbital configuration, the spin-coupled wavefunction provides a significant energy improvement over the corresponding restricted Hartree–Fock calculation. The spin-coupled description of the SO and S–F bonding, and of the non-bonding electrons on sulfur, turns out to be highly transferable. We find that the S–O π bonds are significantly more polar than the S–O σ bonds. We find no evidence to support notions of p π –d π back-donation from oxygen to sulfur. We examine also the ‘equivalent’ or ‘bent-bond’ model of the SO units in the thionyl fluorides.