From the reaction of in situ generated 1,2-di(4-tert-butylphenyl)ethylene-1,2-dithiol, (LH2)-L-2, and Na[AuCl4]center dot 2H(2)O in 1,4-dioxane, green brown crystals of diamagnetic [N(n-Bu)(4)][Au-III(L-2)(2)] (1) were obtained. As shown by cyclic voltammetry, 1 is a member of an electron-transfer series comprising the dianion [Au-II(L-2)(2)](2-), the monoanion [Au-III(L-2)(2)](-), the neutral species [Au-III(L-2(center dot))(L-2)](0) <-> [Au-III(L-2)(L-2(center dot))](0), and the monocation [Au-III(L-2(center dot))(2)](+). (L-2(center dot))(1-) represents the pi radical anion (S-rad = (1)/(2)) of the one-electron oxidized closed-shell dianion (L-2)(2-). Oxidation of 1 in CH2Cl2 with ferrocenium hexafluorophosphate affords green, paramagnetic microcrystals of [Au-III(L-2(center dot))(L-2)] <-> [Au-III(L-2)(L-2(center dot))] (2) (S = (1)/(2)). Complexes 1 and 2 have been characterized by X-ray crystallography. Both species possess square-planar monoanions and neutral molecules, respectively. From the oxidation reaction of 1 or [N(n-Bu)(4)][Au-III(L-3)(2)] with 2-3 equiv of [NO]BF4 in CH2Cl2, a green solution of [Au-III(L-2(center dot))(2)](+) and green microcrystals of [Au-III(L-3(center dot))(2)]BF4 (3) were obtained, respectively; (L-3)(2-) represents the dianion 1,2-di(4-diphenyl)ethylene-1,2-dithiolate, and (L-3(center dot))(1-) is its pi radical monoanion. The electronic structures of this series of gold species have been elucidated by UV-vis, EPR spectroscopies, and DFT calculations. It is shown computationally by density functional theoretical (DFT) methods that the electronic structure of [Au-III(L-1(center dot))(2)](+) is best described as a singlet diradical (S-t = 0); the ligand mixed valency in the neutral species 2 is of class (III) (delocalized); the monoanion in 1 contains a Au-III ion and two closed-shell dianionic ligands; and the corresponding dianions [Au(L)(2)](2-) are best described as an intermediate Au-II/Au-III species with a metal-ligand delocalized SOMO (25% Au 5d, 75% 3p of four S atoms). (L-1)(2-) is the dianion 1,2-di(phenyl)ethylene-1,2-dithiolate, and (L-1(center dot))(1-) is the pi radical monoanion. The neutral species [Pd-II(L-2(center dot))(2)] (4) has also been synthesized and characterized by X-ray crystallography. Its electronic structure is the same as described for [Au-III(L-1(center dot))(2)](+) (singlet diradical), whereas that of the monoanion [Pd-II(L-2(center dot))(L-2)](-) <-> [Pd(L-2)(L-2(center dot))](-) corresponds to that of the neutral gold complex 2. Anodic oxidation of the analogous monoanion [Au-III(mnt)(2)](-), where mnt = maleonitriledithiolate, gave the neutral complex [Au(mnt)(mnt(center dot))] (E-1/2 = 0.91 V vs Fc(+)/Fc). The optical and EPR spectroscopies of [Au(mnt)(mnt(center dot))] were consistent with those observed for the corresponding di(tert-butylphenyl)ethylenedithiolate complex 2.