MOLECULAR COMPLEXES OF SULPHUR DIOXIDE WITH N,O-CONTAINING ORGANIC BASES (REVIEW)

Abstract

The literature data on the synthesis, stoichiometry, structure and relative stability of molecular complexes of sulphur dioxide with N,O-containing organic bases have been systematized and generalized. It was shown that the yield of the reaction product of sulfur dioxide with organic bases (such as amines) are strongly influenced by the conditions of synthesis: the nature of the solvent (basicity, polarity), the temperature and SO2:L ratio in the reaction medium. The stoichiometry of SO2*nL molecular complexes depends on ligand denticity, as well as its ability to H-bonding. The reaction of the sulfur oxide (IV) with organic bases can give S←N and S←O complexes. With the increase of the value of base proton affinity the decrease ΔrSN values has been marked. Characteristic parameter Δr SN = r SN – a1(rS+ rN) (where rSNis the S←N donor-acceptor bond length) has been determined by microwave spectroscopy and X-ray analysis, rSand rNwere the tabulated values of the homopolar covalent radii of sulphur and nitrogen heteroatoms. The dependence of formation enthalpy of molecular complexes of basic amines and spectral characteristics has been noted; enthalpy-entropy compensation for S←N and S←O complex-es has been stated. Despite the limited experimental data on the thermodynamics of complex formation and the lengths of donor-acceptor bonds for the same compounds it has been found bond S←N strength in SO2 molecular complexes to depend on the intrinsic value of ΔrSN. The contribution of van der Waals forces and charge transfer forces to the formation of molecular complexes of sulphur dioxide has been stated.