Electronic structure of H₂S, SF₂, and HSF and implications for hydrogen-substituted hypervalent sulfur fluorides

It is well known that hypervalent molecules are more stable with very electronegative ligands such as fluorine. For example, while SF₆ is uniquely stable and experimentally well characterized and many of the features of SF₄ have been characterized, neither H₄S nor H ₆S has been observed. Furthermore, no hypervalent sulfur species with mixed hydrogen and fluorine ligands have been experimentally characterized to date. In this work, we present detailed calculations of the electronic structure of H₂S, SF₂, and HSF. While all three compounds have similar bent singlet ground states, the potential energy surfaces of various low lying electronic states as a function of bond angle reveal very different behaviors, in particular for linear geometries. We use the disparate bonding motifs of the low-lying triplet states to rationalize the differences between SF₄ and the hypothetical H₄S molecule. We also make predictions about the effects of hydrogen substitution on the energetics and geometries of hypervalent sulfur fluoride compounds.