The Reaction of the Aquopentamminechromium(III) Complex Ion in Aqueous Solution. I. Substitution Reaction of a Coordinated Water with a Chloride Ion

Abstract

Abstract The substitution reaction of aquopentamminechromium(III) ion in which a coordinated water molecule is replaced by a chloride ion was investigated spectrophotometrically. The reaction proceeds according to the second order rate law, d[[Cr(NH3)5Cl]2+]/dt=\overrightarrowk2[[Cr(NH3)5OH2]3+]. [Cl−], and the rate constant varies regularly with the ionic strength of solution according to the Debye-Hückel type equation. The formation of outer sphere association complex in the solution was detected from the change in ultraviolet absorption. From these results the ratedetermining process of this reaction was inferred to be a unimolecular process through the outer sphere association complex. The experimental activation energy and the frequency factor of this reaction were determined to be 24.6 kcal.mol−1 and 1.2×1014l. mol−1min−1 (ω∼0.52), respectively. The aquation of chloropentamminechromium(III) ion was also studied in the solutions of various ionic strengths and the reaction rate was found to vary to some extent with ionic environment.