Notes. Kinetics and mechanism of the oxidation of ruthenium(II) ammines by tetra-ammine(oxalato)- and penta-ammine(hydrogenoxalato)-cobalt(III) complexes

Abstract

The oxidations of [Ru(NH₃)₆]²⁺ and [Ru(NH₃)₅(OH₂)]²⁺ by [Co(NH₃)₄(C₂O₄)]⁺ and [Co(NH₃)₅(HC₂O₄)]²⁺ have been investigated at an ionic strength of 0.20 mol dm^–3(LiCl) at various acid (HCl) concentrations. The oxidation of both ruthenium(II) species by [Co(NH₃)₄(C₂O₄)]⁺ is acid-independent whereas that by [Co(NH₃)₅(HC₂O₄)]²⁺ is acid-inhibited. The activation parameters ΔH^‡(kJ mol^–1) and ΔS^‡(J K^–1 mol^–1) for the reactions of [Co(NH₃)₄(C₂O₄)]⁺ with [Ru(NH₃)₆]²⁺ and [Ru(NH₃)₅(OH₂)]²⁺ are respectively: 60.5 ± 5.9, –24.6 ± 3.1; 66.3 + 6.1, –11.9 ± 1.8. All the reactions studied occur by an outer-sphere mechanism.