Kinetics of aquation of the fluoropentaamminecobalt(III) ion

Abstract

The kinetics of the hydrogen-ion-independent pathway for the replacement of fluoride in aqueous (NH₃)₅CoF²⁺ by H₂O 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 ML₅Xⁿ⁺ is discussed.