Ab initio calculation of the thermochemical properties of polysulphanes (H2Sn)

Thermochemical properties of gaseous polysulphanes (H2Sn) were calculated using the G2 and CBS-Q ab initio theoretical methods. The temperature dependence of the heat capacities and entropies for the polysulphanes are computed between 300 and 1000 K. The difference between the available experimental heat capacity of disulphane (298 K) and the calculated one is found to be quite small (0.7 cal/mol K). The latter is indicative of hindered internal rotation in polysulphanes. Ab initio calculations of rotational barriers in polysulphanes show that the relatively high barriers of internal rotations can be due to the interplay of attractive stabilization, π-character of the S–S bonds (due to hyperconjugation effects) and the participation of the sulphur 3d orbitals in bonding.