Reactions of µ-hydroxo-dicobalt(III) complexes. Part XII. Equilibrium and kinetic studies on hydroxo-bridge cleavage reactions of two triply-bridged dicobalt(III) complexes in aqueous perchloric acid solutions

Abstract

The equilibration kinetics of the first hydroxo-bridge cleavage of the triply-bridged complexes tri-µ-hydroxo-bis[triamminecobalt(III)], [(NH3)3Co·µ(OH,OH,OH)·Co(NH3)3]3+, (I), and µ-amido-di-µ-hydroxo-bis[tri-amminecobalt(III)], [(NH3)3Co·µ(NH2,OH,OH)·Co(NH3)3]3+, (II), have been studied, I= 1·0M(LiClO4). Within the range [H+]= 0·01–0·5M first-order rate constants, kobs, for the equilibration of (I) fit the dependence (i)kobs=k1KP[H+]//1 +KP[H+]+k–1(i) where KP, k1, and k–1 are for the reaction sequence (ii) and (iii). [graphic omitted] (ii), [graphic omitted] (iii) At 25 °C KP= 1·51 (±0·18) l mol–1, k1= 1·86 (±0·15)× 10–1 s–1, and k–1= 6·62 (±0·36)× 10–3 s–1. For (II) the dependence of kobs′ on [H+] is of the simpler form (iv), kobs′=k2KP′[H+]+k–2(iv) and at 25 °C KP′ <0·05 l mol–1, k2KP′= 1·01 (±0·02) l mol–1 s–1, and k–2= l·96 (±0·4)× 10–2 s–1. Activation parameters for k1, k–1, k2KP′, and k–2 have been determined. Equilibrium data have also been evaluated from spectrophotometric measurements.