The radical cations of sulphur (S8˙+) and tetrasulphur tetranitride (S4N4˙+): a radiation–electron spin resonance study

Abstract

Exposure of dilute solutions of S₈ and S₄N₄ in trichlorofluoromethane to ⁶⁰Co γ-rays at 77 K gave the corresponding radical cations. The first formed species from sulphur, (A), thought to be S₈⁺, had g_x= 2.069, g_y= 2.057, and g_z= 1.997. Enrichment (99%) with ³³S gave greatly broadened x and y features, with A(³³S)≈± 4 G. The z features showed a clear central line flanked by others with A_Z≈ 28 G. The results suggest the presence of two equally coupled sulphur atoms. On annealing, species (A) changes irreversibly into species (B)(g_x= 2.044, g_y= 2.034, g_z= 2.0035). It is suggested that (B) is also S₈˙⁺ in a relaxed form in which two opposite atoms have formed a weak three-electron bond. The e.s.r. parameters for (B) are very similar to those previously assigned to S₈⁺, formed from S₈²⁺ in oleum. A clear spectrum was produced from S₄N₄ which showed little g-value variation (g_av= 2.004) and no evidence for ¹⁴N splitting. It is concluded that the S₄N₄˙⁺ cation has a relatively isolated semi-occupied molecular orbital, with low spin density on nitrogen.