The trans-effect in octahedral complexes. Part IV. Kinetic trans-effect of OH–, OH2, and NH3 in complexes of the form trans-RhA2L(OH2)n+, where A = ethylenediamine (en)

Abstract

Anation reactions of trans-Rh en₂L(OH₂)ⁿ⁺(where L = OH^–, OH₂, or NH₃) have been studied over a temperature range. Consideration of the kinetic parameters enables a quantitative measure of the kinetic trans-effects of OH^–, OH₂, and NH₃ to be obtained. These are compared with those of NH₃ and the halide ions obtained previously. In terms of the enthalpies of activation, H₂O has the lowest trans-effect yet found in these rhodium complexes, while OH^– and NH₃ have a trans-effect close to that of the chloride ion. The activation entropy for the anation of the diaquo-complexes is much more positive than that of the aquopenta-amminerhodium(III) complex, the latter being thought to react via an associative mechanism. Therefore, the trans-diaquo-complex, like the hexa-aquo-complex, probably reacts via a dissociative mechanism.