Polysulfite, a hypothetical allotrope of sulfur dioxide? A molecular and periodic quantum investigation of covalent oligomeric and one-dimensional XO_2-based compounds (X=S,Se)

摘要

Covalent oligomeric and polymeric phases of SeO_2 and SO_2 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 SO_2 , is calculated to be energetically less stable than free molecular sulfur dioxide by less than 11 kcal mol-l. This small energy difference #delta#E 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 SeO_2 by 20 kcal mol-l. 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 X_2O_4 (X = S, Se; C_2v and C_2h symmetry) and S_40S (D4J are also investigated at the B_3L YP level using extended basis sets.