The synthesis, electrochemical and spectroelectrochemical properties of (TMA)[Rh(ox)(CO)2], (TMA)[Rh(ox)(COD)] and [Rh2(ox)(COD)2], where TMA is tetramethylammonium, COD is 1, 5-cyclooctadiene and ox is oxalate dianion, are reported. The monometallic complexes, (TMA)[Rh(ox)(CO)2] and (TMA)[Rh(ox)(COD)], can be oxidized by two electrons. However their oxidation is followed by a chemical reaction to form a solvated Rh complex and two equivalents of CO2 due to decomposition of the oxalate. The bimetallic complex, [Rh2(ox)(COD)2], is oxidized electrochemically in two successive two-electron steps without decomposition of the coordinated oxalate. An equilibrium reaction between [Rh(ox)(COD)]-, [Rh(COD)(CH3CN)2]+ and [Rh2(COD)2(ox)] is present which complicates the electron transfer mechanism. Chemical oxidations of (TMA)[Rh(ox)(COD)] and [Rh2(ox)(COD)2] were performed to further establish the products of the oxidation reactions and the formation of [Rh2(CH3CN)(COD)2(ox)]BF4 is reported. © 1993.