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][AuIII(Lt-Bu)2] (1) reacts with iodine in acetone affording the neutral paramagnetic species [Au(Lt-Bu)2] (1a) (S = 1/2) where H2[Lt-Bu] represents the ligand 3,5-di-tert-butyl-1,2-benzenedithiol. The corresponding complexes containing the unsubstituted ligand H2[L], 1,2-benzenedithiol, namely [N(n-Bu)3H][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. 197Au 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 mixedvalent species 1a 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.