Electrochemistry of Ruthenium Ammine Complexes

Abstract

The electrochemistry of ruthenium(III) penta- and tetraammine chloro complexes has been investigated. In each case, the ruthenium(III) species was found to undergo an initial one electron reduction step, followed by hydrolysis of the chloride(s) in the ruthenium(II) product. The rate constants for the substitution steps were evaluated by cyclic voltammetry. An aqueous 0.30 M methane sulfonate electrolyte of pH 2.0 was used at 25 °C.Values for the reversible "E 1/2 " (V υs. SCE) and first order rate constants for the (stepwise) replacement of the Cl − are: Ru(NH 3 ) 5 Cl + , −0.282 V and 17 s −1 ; cis-Ru(NH 3 ) 4 Cl 2 + , −0.328 V, 80 s −1 , and 5 s −1 ; trans-Ru(NH 3 ) 4 Cl 2 + , −0.412 V, 2 s −1 , and 0.4 s −1 .The electrochemistry of Ru(NH 3 ) 5 SO 2 2+ was also investigated. In a 0.10 M CH 3 SO 3 H – 0.20 M CH 3 SO 3 Na electrolyte the ruthenium(II) species was found to undergo an initial one electron oxidation step with "E 1/2 " = +0.50 V, followed by a slow hydrolysis of the SO 2 in the ruthenium(III) product with k = 2.4 × 10 −2 s −1 at 25 °C.