Molecular complexes formed by the interaction of hydrogen sulphide H 2 S with silanol H 3 Si(OH), two model Bronsted acid sites of zeolite clusters H 3 Si(OH)AlH 3 and H 3 Si(OH)Al(OH) 2 SiH 3 and a sodium zeolite cluster H 3 Si(ONa)Al(OH) 2 SiH 3 have been studied by ab initio methods. Both Hartree-Fock (HF) and post-Hartree-Fock (MP2) levels of theory were used. The geometries of the isolated molecules and the corresponding complexes were optimized at the HF/6031G * * level of theory, assuming C s symmetry for the complexes. Corresponding geometry optimizations at the MP2/6-31G * * level of theory were also carried out for the H 2 S-silanol and the H 2 S-H 3 Si(OH)AlH 3 complexes. Comparisons with similar water-zeolite complexes are made. The HF harmonic vibrational frequencies of the OH and SH stretching modes of these complexes are compared with experimental infrared measurements.