The First Step of the Oxidation of Elemental Sulfur: Crystal Structure of the Homopolyatomic Sulfur Radical Cation [S8]•+

The oxidation of elemental sulfur in superacidic solutions and melts is one of the oldest topics in inorganic main group chemistry. Thus far, only three homopolyatomic sulfur cations ([S-4](2+), [S-8](2+), and [S-19](2+)) have been characterized crystallographically although ESR investigations have given evidence for the presence of at least two additional homopolyatomic sulfur radical cations in solution. Herein, the crystal structure of the hitherto unknown homopolyatomic sulfur radical cation [S-8](center dot+) is presented. The radical cation [S-8](center dot+) represents the first step of the oxidation of the S-8 molecule present in elemental sulfur. It has a structure similar to the known structure of [S-8](2+), but the transannular sulfur center dot center dot center dot sulfur contact is significantly elongated. Quantum-chemical calculations help in understanding its structure and support its presence in solution as a stable compound. The existence of [S-8](center dot+) is also in accord with previous ESR investigations.