Comparison of the C—H...O bonding in two crystalline phases of 1,4-dithiane 1,1,4,4-tetraoxide

Abstract

The crystal structures of two crystalline phases of 1,4-dithiane 1,1,4,4-tetraoxide, C4H8O4S2, have been determined in order to examine the nature of possible intermolecular hydrogen bonds. Phase 1 is monoclinic, space group C2/m, with unit-cell dimensions of a = 9.073 (8), b = 7.077 (6), c = 5.597 (5) Å and β = 105.89 (1)°. The molecule adopts 2/m symmetry and all of the molecules are related by translation and thus have the same orientation. Phase 2 is also monoclinic but in space group P21/n with unit-cell dimensions of a = 7.1305 (5), b = 5.7245 (4), c = 8.3760 (6) Å and β = 91.138 (2)°. In this phase, the molecule sits on an inversion center and the molecules within the unit cell adopt quite different orientations. In both phases, examination of the potential C—H...O hydrogen bonds around each of the independent oxygen atoms (one axial and the other equatorial) shows the general O...H patterns to be quite similar with each oxygen atom in contact with four neighboring H atoms, and each H atom contacting two neighboring O atoms. While none of the H...O contacts is particularly short (all are greater than 2.5 Å), each molecule has 32 such contacts that form an extensive intermolecular network. A 1H NMR spectrum of the compound dissolved in DMSO shows a singlet of 8H at δ 3.677 which indicates that the C—H bonds are only moderately polarized by the single adjacent –SO2– moiety: strongly polarized C—H bonds have δ values in the 5–6 range [Li & Sammes (1983). J. Chem. Soc. Perkin Trans. 1, pp. 1303–1309]. The phase 1 crystal studied was non-merohedrally twinned.