Nature of the Paramagnetic Cation in Solutions of Sulphur in Oleum

Abstract

SINCE the discovery that blue solutions of sulphur in oleum contain a paramagnetic species^1,2, theories regarding its identity have abounded. Recently two accounts of the e.s.r. spectra of the interesting blue solutions formed by dissolution of elemental sulphur in 65% oleum have appeared^3–5. In the first, for which sulphur enriched with 25% ³³S was used, a seven line e.s.r. spectrum was interpreted in terms of the ion S₈⁺, because a simulation of the spectrum seemed to favour eight equivalent sulphur atoms rather than the four required by S₄⁺. The differences were small, however, and more weight was placed on the results at 77 K which clearly required that the sulphur atoms were not equivalent. This seemed to rule out S₄⁺. Only S₄⁺ and S₈⁺ were seriously considered because of the convincing work of Gillespie et al.⁶, who consider that the blue oleum solutions contain S₄⁺ rather than S₈⁺.