Terence P. Cunningham, David L. Cooper, Joseph Gerratt, Peter B. Karadakov and Mario Raimondi
Modern valence bond theory, in its spin-coupled form, is used to
investigate the bonding in sulfuryl fluoride,
SO2F2, and in the thionyl fluorides,
SOF2 and SOF4. Analogous calculations are also
carried out for SO2, SO3 and SF4, 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
pπ–dπ back-donation from oxygen to
sulfur. We examine also the ‘equivalent’ or
‘bent-bond’ model of the SO units in the thionyl
fluorides.