Electrochemical properties of the newly synthesized 2-amino thiophenolatobis (2,2'-bipyridine)ruthenium(II) [Ru(bpy)(2)(NH2. S)cat](+) (bpy = 2,2'-bipyridine, (NH2. S) = 2-aminothiophenolate) are reported, using microelectrode, disk electrode, rotating disk electrode cyclic voltammetry, spectroelectrochemistry, and differential pulse voltammetry. The results are compared with the electrochemical properties of the previously studied [Ru-II(bpy)(2)-LL](n+) compounds, where LL are 1,2-dihydroxybenzene (O . O), 2-aminophenol (NHm. O), and 1,2-diaminobenzene (NHm. NHm). These ligands can exist in protonated (m = 2) or deprotonated (m = 1) forms. By means of cyclic voltammetry, the deprotonated [Ru-II(bpy)(2)(NH . S)](0) displayed a series of one-electron reversible redox waves, consistent with the previously observed results for the [Ru-II(bpy)(2)LL](n+) complexes. However, the reversible waves observed for protonated [Ru-II(bpy)(2)(NH2. S) cat](+) are inconsistent with the irreversible waves observed for protonated [Ru-II(bpy)(2)LL](n+) complexes. An ECE mechanism is proposed to account for these differences and is used to interpret and simulate the cyclic voltammograms (CV)s of [Ru-II(bpy)(2)(NH2. S)cat](+) in organic solvents.