Preparation and crystal structures of the isomeric series 4-tolyl-1,2,3,5-dithiadiazolyl, (o-MeC6H4CNSSN)2, (m-MeC6H4CNSSN)2 and (p-MeC6H4CNSSN)2

Abstract

The radicals (p-MeC₆H₄CNSSN)₂ (1) (m-MeC₆H₄CNSSN)₂ (2) and (o-MeC₆H₄CNSSN)₂ (3) were prepared from the corresponding tolunitriles using conventional synthetic methodologies and were crystallised by vacuum sublimation. All three structures comprise cis-cofacial π*–π* dimers with one dimer in the asymmetric unit for 1 and 2 and four dimers in the asymmetric unit for 3. In both 1 and 2 the crystal packing reveals close S⋯π(aryl) interactions which drive formation of a double herringbone motif, analogous to that observed in the parent radical [PhCNSSN]₂. The double herringbone sheets in both 1 and 2 are linked via S^δ+⋯N^δ− contacts. The presence of the methyl group in the ortho-position has a pronounced effect on the solid state structure of 3; the steric demand of the ortho-methyl group generates a substantially larger twist angle between aryl and heterocyclic rings (19.43–28.07° in 3 compared with 5.20–10.91° in 1 and 2). This induces a larger mean intra-dimer separation (mean S⋯S = 3.117(2) Å, cf.1 and 2 at 3.0759(9) and 3.078(1) Å) and also inhibits formation of S⋯π interactions in 3. Instead the structure of 3 reveals a layered arrangement of dimers with intra-layer S^δ+⋯N^δ− contacts. The lengthening of the intramolecular S⋯S bond in 3 leads to a weakening of the π*–π* dimer and is manifested in the observation of a thermally accessible triplet state (S = 1) at room temperature by EPR spectroscopy. Warming above room temperature leads to a rapid increase in EPR intensity above 320 K associated with melting of 3.