AN AB-INITIO STUDY OF THE MOLECULAR-COMPLEXES FORMED BETWEEN H2S AND THE ACID SITES OF ZEOLITES

Molecular complexes formed by the interaction of hydrogen sulphide H2S with silanol H3Si(OH), two model Bronsted acid sites of zeolite clust ers H3Si(OH)AlH3 and H3Si(OH)Al(OH)(2)SiH3 and a sodium zeolite cluste r H3Si(ONa)Al(OH)(2)SiH3 have been studied by ab initio methods. Both Hartree-Fock (HF) and post-Hartree-Fock (MP2) levels of theory were us ed. The geometries of the isolated molecules and the corresponding com plexes were optimized at the HF/6-31G* level of theory, assuming C-s symmetry for the complexes. Corresponding geometry optimizations at th e MP2/6-31G* level of theory were also carried out for the H2S-silano l and the H2S-H3Si(OH)AlH3 complexes. Comparisons with similar water-z eolite complexes are made. The HF harmonic vibrational frequencies of the OH and SH stretching modes of these complexes are compared with ex perimental infrared measurements.