Polysulfite, a hypothetical allotrope of sulfur dioxide? A molecular and periodic quantum investigation of covalent oligomeric and one-dimensional XO2-based compounds (X=S, Se)

Abstract

Covalent oligomeric and polymeric phases of SeO2 and SO2 have been investigated at high levels of density functional calculations on molecular and periodic models. Polysulfite [–S(O)O–]x, a one-dimensional allotropic form of SO2, is calculated to be energetically less stable than free molecular sulfur dioxide by less than 11 kcal mol−1. This small energy difference δE renders polysulfite a candidate for experimental investigation. Its valence isoelectronic analog, the crystalline downeyite phase with linear [–Se(O)O–]x chains, is more stable than the molecular species SeO2 by 20 kcal mol−1. Substituting sulfur for selenium in the one-dimensional [–Se(O)O–]x structure containing sp3 chalcogen atoms slightly favors the 18-valence electron triatomic species. This feature may be related to the s–p energy difference, which diminishes on going down group 16. Finite molecular aggregates such as the four-membered rings X2O4 (X = S, Se; C2v and C2h symmetry) and S4O8 (D4h) are also investigated at the B3LYP level using extended basis sets.