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

Abstract

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 ] , [S ] , and [S ] ) 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 ] is presented. The radical cation [S ] represents the first step of the oxidation of the S molecule present in elemental sulfur. It has a structure similar to the known structure of [S ] , but the transannular sulfur⋅⋅⋅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 ] is also in accord with previous ESR investigations.

Synthesis, Electronic Structures, and Electrochemistry of 3‐Triarylphosphoraniminato‐1,3,5‐trithia‐2,4,6,8‐tetrazocines: Detection of Trithiatetrazocinyl Radical Anions

“…For example, the transannular S2⋅⋅⋅S3 contact in 5 d is 2.4369(8) Å, which cannot be differentiated from that found in 4 d at the 95 % confidence level. Similar transannular contacts have been observed in mono‐ and dications of S 8 rings by crystallography as reported very recently …”

“…Similar transannular contacts have been observed in monoand dications of S 8 rings by crystallography as reported very recently. [20]…”

Homopolyatomic Chalcogen Radical Cations of Selenium and Tellurium

“…The radical cation [S 5 ] + was unambiguously identified by ESR spectroscopy using 33 S enriched sulfur in superacidic solution . Structures of homopolyatomic cationic chalogen radicals could not be determined until our recent publication on the crystal structure of the [S 8 ] + radical cation stabilized by a weakly coordinating boron cluster anion in the solid state . This open shell radical cation has a structure related to that of the previously known [S 8 ] 2+[25] dication but possesses a significantly elongated transannular contact, which was reproduced by DFT calculations and is in accord with a theoretical bonding model .…”

“…Structures of homopolyatomic cationic chalogen radicals could not be determined until our recent publication on the crystal structure of the [S 8 ] + radical cation stabilized by a weakly coordinating boron cluster anion in the solid state . This open shell radical cation has a structure related to that of the previously known [S 8 ] 2+[25] dication but possesses a significantly elongated transannular contact, which was reproduced by DFT calculations and is in accord with a theoretical bonding model . DFT calculations taking solvation effects into account indicate that in liquid sulfur dioxide [S 5 ] + and [S 8 ] + should be thermodynamically stable radical cations and that [S 7 ] + might be a borderline case .…”

“…The chalcogens sulfur, selenium and tellurium are able to form stable element‐element bonds, which results in the formation of various neutral and charged homopolyatomic rings, chains and clusters Sulfur preferentially forms neutral rings of different sizes and negatively charged polysulfides,, but some cations are known as well , . In contrast, the heavier elements selenium and tellurium show a higher tendency to form cationic clusters.…”