Dimers, trimers and oligomers of sulfur oxides: an ab initio and density functional study

Ab initio (HF/3-21G*), DFT (B3LYP with basis sets 6-31G*, 6-311 + G* and 6- 311 + G(2d)) and, in some cases, MP2/631G* calculations, were done on cycli c dimers, trimers, etc, and on acyclic oligomers (with OH and H on the ends ) of sulfur monoxide and sulfur dioxide. The four cyclic (SO)(n) molecules were (S-O)(2) (1,3,2,4-dioxadithietane, 1a), (S-O)(3) (1,3,5,2,4,6-trioxatr ithiane, 2a), (S(=O))(4) (tetrathietane 1,2,3,4-tetraoxide, 1b), and (S(=O) )(6) (hexathiane 1,2,3,4,5,6-hexaoxide, 2b). The four cyclic (SO2)(n) molec ules were the dioxide of 1a (1,3,2,4-dioxadithietane 2,4-dioxide, 1c), the trioxide of 2a (1,3,5,2,4,6-trioxatrithiane 2,4,6-trioxide, 2c), the tetrao xide of 1b (tetrathietane 1,1,2,2,3,3,4,4-octaoxide, 1d) and the hexaoxide of 2b (hexathiane 1,1,2,2,3,3,4,4,5,5,6,6-dodecaoxide, 2d). The 16 acyclic molecules (oxides of disulfane, trisulfane, etc. and oxides of oxadisulfane , dioxatrisulfane, etc.) were (-S-O-)(n), (-S(=O)-)(n), (-S(=O)O-)(n), and (-S(=O)(2)-)(n), with n from 2 to 5 and HO, H at the ends. Most of these sp ecies are relative minima on the B3LYP/6-31G* potential energy surface. In energy content, the SO dimer, etc. lie below, and the SO2 dimer, etc. above , their SOx, components, at all the electron-correlated levels. (C) 2000 El sevier Science B.V. All rights reserved.