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 kobs.=(k1+kx[X–])[CrII], 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.