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

Abstract

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.