We report on a mechanistic investigation regarding the reduction of [Co-III(dmgH)(2)(py)(Cl)] (dmg = dimethylglyoxime) by several complementary techniques. The reduction of [Co-III(dmgH)(2)(py)(Cl)] was initiated by either electrochemical, photochemical, or pulse radiolytical techniques, and the corresponding products were analyzed by ESI mass spectrometry. In addition, all of the rate constants for each step were determined. We have found solid experimental as well as theoretical evidence for the appearance of a dinuclear complex [(CoCoIII)-Co-II(dmgH)(4)(py)(2)(H2O)(2)](+) to be the final product of reduction, implying the initially reduced form of [Co-III(dmgH)(2)(py)(Cl)] undergoes a dimerization with the starting material in solution.