AB-INITIO STUDIES ON HALOSULFITE IONS

High level ab initio studies were performed to investigate the stability of halosulfite ions. The basis set 6-31+G(3df) was used for the fluorosulfite and chlorosulfite ions. Pseudopotential functions were used for describing the core electrons of the heavier halogen atoms. Hartree-Fock and MP2 optimizations were carried out and various levels of theory up to QCISD(T) were used for the energy calculations. Additional calculations were performed to investigate the stability of the ions in polar environments. The calculated stability trend with respect to halosulfite ion formation from SO2 and the halide ion (SO2F-(approximate to 50 kcal mol(-1)) much greater than SO2Cl-(approximate to 20 kcal mol(-1) > SO2Br-(approximate to 18 kcal mol(-1)) > SO2I-(approximate to 13 kcal mol(-1)) is in agreement with the experimentally observed trend. From these calculations, only the fluorosulfite ion appears to be stable in polar solvents, while all the other anions may dissociate.