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

Abstract

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)Å, 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)Å, 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.