AB-INITIO CALCULATION OF THE THERMOCHEMICAL PROPERTIES OF POLYSULPHANES (H2SN)

Thermochemical properties of gaseous polysulphanes (H2Sn) were calcula ted using the G2 and CBS-Q ab initio theoretical methods. The temperat ure dependence of the heat capacities and entropies for the polysulpha nes are computed between 300 and 1000 K. The difference between the av ailable experimental heat capacity of disulphane (298 K) and the calcu lated one is found to be quite small (0.7 cal/mol K). The latter is in dicative of hindered internal rotation in polysulphanes. Ab initio cal culations of rotational barriers in polysulphanes show that the relati vely high barriers of internal rotations can be due to the interplay o f attractive stabilization, pi-character of the S-S bonds (due to hype rconjugation effects) and the participation of the sulphur 3d orbitals in bonding. (C) 1998 Elsevier Science B.V. All rights reserved.