Kinetics of aquation of the fluoropentaamminecobalt(III) ion

Abstract

The kinetics of the hydrogen-ion-independent pathway for the replacement of fluoride in aqueous (NH 3 ) 5 CoF 2+ by H 2 O have been reinvestigated using a specific fluoride-ion electrode, with due regard for the concomitant autocatalytic loss of the ammine ligands. In perchlorate media of ionic strength 0.1 M, the first-order rate coefficient is 1.22 × 10 −6 s −1 at 45°, and the kinetics are represented by ΔH* = 24.4 kcal mole −1 and ΔS* = −9 cal deg −1 mole −1 over the range 35–75° at least. The relationship of these data to those for the aquation of other species of the type ML 5 X n+ is discussed.