Preparation and crystal structure of the paramagnetic solid F3CCSSSCCF3AsF6: implications for the identity of RCSSCR˙+

Abstract

4,5-Bis(trifluoromethyl)-1,2,3-trithiolylium hexafluoroarsenate, which contains the 7π F3C[graphic omitted]CF3˙+ radical cation, the first example of a cationic carbon–sulfur heterocycle, has been prepared and characterised. It was prepared as a purple solid in 90% yield by the reaction of F3CCCCF3 with a 1 : 1 mixture of S4(AsF6)2 and S8(AsF6)2 in SO2 at 50 °C for 2 weeks. Small amounts of a homopolyatomic sulfur cation (probably S82+) were removed by work-up with fresh F3CCCCF3 and AsF5 in SO2 at 50 °C for 8 d. The F3C[graphic omitted]CF3AsF6 was characterised in the solid state by chemical analyses, IR, mass spectrometry [M+ at m/z 258 (100%)] and X-ray crystallography. The crystal structure consists of layers containing both monomeric, planar F3C[graphic omitted]CF3˙+ radical cations and AsF6– anions [space group Pnma, a= 12.241(4), b= 8.232(5), c= 37.39(3)A, Z= 12 and R= 0.086]. A powder photograph of the bulk product correlated with the single-crystal data, and a variable-temperature magnetic susceptibility study indicated that F3C[graphic omitted]CF3AsF6 is a paramagnetic solid, exhibiting ordinary Curie–Weiss behaviour, µ= 1.68, θ=–0.6 K (µ= 2.1 in SO2 solution at room temperature). The ESR spectrum of F3C[graphic omitted]CF3˙+ in SO2 is identical to that previously reported for F3C[graphic omitted]CF3˙+[g= 2.014, a(19F)= 1.3 G, ‘a(33S)’= 8.6 G], which suggested that spectra long assigned to 1,2-dithiete cations are in fact due to 1,2,3-trithiolylium cations. This is supported by the ESR spectrum of MeO2C[graphic omitted]CO2Me˙+, which consisted of a singlet at g= 2.017, with two sets of 33S satellites in a 2:1 intensity ratio, with very similar 33S coupling constants (8.0 and 8.9 G). The salt F3C[graphic omitted]CF3AsF6 is reduced by KI to give a mixture of neutral cyclic polysulfides including F3C[graphic omitted]CF3(43%) and the previously unknown F3C[graphic omitted]CF3(23%). Attempts to oxidise F3C[graphic omitted]CF3˙+ with AsF5 were unsuccessful.