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

The crystal structures of two crystalline phases of 1,4-di­thiane 1,1,4,4-tetra­oxide, C(4)H(8)O(4)S(2), 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 P2(1)/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 (1)H 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 –SO(2)– 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.