Do S,S′-coordinated o-dithiobenzosemiquinonate(1-) radicals exist in coordination compounds?: The [AuIII(1,2-C6H4S2)2]1-/0 couple

The square planar, light-green, diamagnetic complex [N(n-Bu)(4)][Au-III(Lt-Bu)(2)] (1) reacts with iodine in acetone affording the neutral paramagnetic species [Au(Lt-Bu)(2)] (1a) (S = 1/2) where H-2[Lt-Bu] represents the ligand 3,5-di-tert-butyl-1,2-benzenedithiol. The corresponding complexes containing the unsubstituted ligand H-2[L], 1,2-benzenedithiol, namely [N(n-Bu)(3)H][Au(L)(2)] (2) and [Au(L)(2)] (2a), have also been prepared and characterized by X-ray crystallography; the structure of the latter has been reported in ref 10. Au-197 Mossbauer spectra of 1 and 1a clearly show that the one-electron oxidation is ligand-centered and does not involve the formation of Au(IV) (d(7)). The spectroscopic features of the ligand mixed-valent species la were determined by UV-vis, EPR, and IR spectroscopy which allows the detection of S,S-coordinated 1,2-dithiobenzosemiquinonate(1-) radicals in coordination compounds.