Kinetics of aquation of hexachloroiridate(III) and of chloride anation of pentachloroaquoiridate(III)

Abstract

A kinetic study of the reversible reaction ▪ by electrophoresis and neutron activation analysis had led to evaluation of rate and equilibrium constants and a discussion of mechanisms. Aquation of IrCl 6 3− was followed at 3–50°C in 0–1·0 M HClO 4 (μ = 0·0025-1·030 M). At 25°C and μ = 0·130 M, k 1 = (3·40±0·05) × 10 − sec −, E α1 =28·11±0·57 Mcal mole −1 and log PZ = 16·13 ± 0·40. At this temperature k 1 is independent of [IrCl 6 3−] 0 (1 and 5mF), of [H +] (10 3−−1·0 M) and of μ (up to 0·04 M). Cl − anation of Ir(H 2 O)Cl 5 2− was studied at 25–50°C and μ=1·030 M, in 1·030 M, in 0·5-1·0 M HCl. In 1·0 M HCl, the pseudo-first order rate constant at 25°C is k −1′ = (0·133 ± 0·003) × 10 −5 sec −1, and {E{in a}−1=28·24 ± 1·03 Kcal mole −1, log PZ = 14·81 ± 0·71}. At this temperature, k −1′ conforms equation k ′=k a[ Cl −]/( k b k c +[ Cl − ] ) where k a =0·382×10 −5 and k b k c=1·85 M. At same temperature and μ=1·030 M, K=12 M. The rate constant for aquation of Ir(H 2O)Cl 5 2− is k 2=(0·119±0·003)×10 −5 sec −1 at 25°C in 0·1 M HClO 4 (μ=0·130 M).