Structural and mechanistic studies of co-ordination compounds. Part 31. The chromium(II) reduction of some trans-tetra-aminedichloro-ruthenium(III) cations

The kinetics of the reduction of trans-[RuLCl₂]⁺ [L = L¹, bis(ethane-1,2-diamine); L², 3,7-diazanonane-1,9-diamine; or L³, 1,4,8,11-tetra-azacyclotetradecane] by chromium(II) have been investigated. These reactions follow the general rate expression k_obs. = (k₁ + k_x[X^-])[Cr^II], where X^- represents either Cl^- or Br^- added to the reaction solutions. The second-order rate constants, k₁, and activation parameters at I = 0.50 mol dm^-3 are: k₁ = 30.2, 47.3, and 64.4 dm³ mol^-1 s^-1; ΔH‡ = 20.3 ± 1.0, 26.6 ± 3.0, and 26.8 ± 1.5 kJ mol^-1; and ΔS‡ = -149 ± 4, -124 ± 12, and -120 ± 6 J K^-1 mol^-1 for L = L¹, L², and L³ complexes respectively. These reactions are consistent with an inner-sphere mechanism.