Ab initio study of the 1,5-dithiacyclooctane radical cation and its dimer dication

An ab initio molecular orbital study of the radical cation of 1,5-dithiacyclooctane and its dimer dication is reported. The calculations performed range from HF/3-21G (∗) to MP2/6-31G ∗ . Nine energy-minimum structures were located for the monomer, of which a boat–chair (BC) form was calculated to be the most stable consistent with the liquid-phase ESR spectra reported. However, barriers to conformational interconversion are predicted to be less than 10 kcal mol −1 for the isolated radical cation, which is not consistent with the ESR results at various temperatures. Therefore, it is likely that the solvent and/or counter ion prevent conformational changes. The dimer is predicted to adopt structures which have a four-center six-electron bond consisting of linearly aligned sulfur atoms.