Preparation of 1,3,2-dithiazolium hexafluoroarsenate(V), preparation and crystal structures of 5-methyl-1,3,2,4-dithiadiazolium and 4-methyl-1,3,2-dithiazolium hexafluoroarsenate(V) and the reduction of these salts to stable free radicals

Crystalline CH3[graphic omitted] AsF6–, CH3[graphic omitted] AsF6–, and [graphic omitted] AsF6– were prepared in essentially quantitative yield by the reaction of S2NAsF6 with CH3CN, CH3CCH, and HCCH respectively, in sulphur dioxide solution. The compounds have been characterised by elemental analysis, i.r. and mass spectrometry. The compound CH3[graphic omitted] AsF6– crystallizes in the monoclinic space group P21/c, with unit-cell dimensions a= 8.182(7), b= 9.822(3), c= 11.515(7)A, β= 110.91(6)°, and Z= 4. The structure was solved from low-temperature diffractometer data by direct methods and refined by least-squares techniques to a final R of 0.12 for 893 observed reflections. The structure consists of discrete, planar CH3[graphic omitted] cations and AsF6– anions with some cation–anion interactions. The compound CH3[graphic omitted] AsF6– crystallizes in the monoclinic space group P21/c, with unit-cell dimensions a= 8.539(5), b= 9.941 (2), c= 12.053(5)A, β= 116.69(4)°, and Z= 4. The structure was solved by direct methods and refined by least-squares techniques to a final R of 0.049 for 1 077 observed reflections. The structure contains the hitherto unknown CH3[graphic omitted] cation and the AsF6– anion with some cation–anion interaction. Both CH3[graphic omitted] and [graphic omitted] (R = H or CH3) can be regarded as 6π cyclic systems. The cations have been reduced chemically and electrolytically to form long-lived free radicals identified by their e.s.r. spectra; INDO calculations have yielded values of hyperfine coupling constants in good agreement with those obtained experimentally.