THE ORIGIN OF THE UNUSUAL C-4-NU STRUCTURE PREDICTED FOR SH4

Ab initio molecular orbital calculations have been performed on C2v an d C4v isomers of SH4, SF4 and S(CH3)4 to investigate the origin of the different structures adopted by these molecules. We propose an electr ostatic model similar in spirit to the VSEPR approach; this implies th at the net charges on the ligands L in SL4 compounds can control the g eometry of these compounds. Steric factors may also be significant. Ev en though the net charges on hydrogen and on the CH3 group are similar when these act as ligands towards sulfur, the carbon atom in the meth yl group bears a substantial negative net charge, which has important structural consequences. Binding energies and structural parameters ar e presented for SH4 which are obtained from more complete theoretical calculations than those previously reported.