
%0 Journal Article
%A Yandell, JK 
%A Tomlins, LA 
%T The <I>trans</I> effect in cobalt(III) complexes. Kinetics and mechanism of substitution of cobalt(III) sulphito complexes
%J Australian Journal of Chemistry
%D 1978/03/01
%V 31
%N 3
%P 561-571
%K 
%R https://doi.org/10.1071/CH9780561
%U https://www.publish.csiro.au/paper/CH9780561 
%X Equilibrium constants K and rate constants kf have been measured, at 25&#176;C and ionic strength of 1.0, for the substitution of the labile water molecule in trans-[aquabis(ethylenediamine)sulphito-cobalt(III)] ion by thiosulphate ion (K = 1.8&#215;102 mol-1 1., kf = 1.27&#215;103 mol-1 1. s-1), thiocyanate ion (2.5&#215;103, 2.75&#215;102), nitrite ion (1.0&#215;103, 2.06&#215;102), azide ion (2.9&#215;102, 2.4&#215;102) ferricyanide ion (-, 1.72&#215;103), hydrogen azide (< 1.2,1.4&#215;10), ammonia (3.0, 6.7) and imidazole (2.6&#215;102, 5.2).     The correlation of these rate constants with charge on the incoming ligand, as well as a decrease in the apparent second-order rate constants observed at high concentrations of the anionic ligands, requires a rapid outer-sphere pre-equilibrium step followed by a rate- determining dissociative interchange of the incoming ligand with the bound water molecule. The activation energy of the thiocyanate substitution was found to be 48 kJ mol-1. Aquation of cis- [azidobis(ethylenediamine)-sulphitocobalt(III)] ion, in the range of hydrogen ion concentration between 10-2 and 0.2 M, was found to give the trans-aquasulphito complex with a first-order rate constant consistent with the equation                              k = 4.9&#215;10-4[H+]+1.0&#215;10-5 s-1  at 25&#176;C and ionic strength 1.0. 
