KINETICS OF AQUATION OF HEXACHLOROIRIDATE(3) AND OF CHLORIDE ANATION OF PENTACHLOROAQUOIRIDATE(3)

A kinetic study of the reversible reaction {A figure is presented} by electrophoresis and neutron activation analysis had led to evaluation of rate and equilibrium constants and a discussion of mechanisms. Aquation of IrCl63- was followed at 3-50°C in 0-1·0 M HClO4 (μ = 0·0025-1·030 M). At 25°C and μ = 0·130 M, k1 = (3·40±0·05) × 10- sec-, Eα1=28·11±0·57 Mcal mole-1 and log PZ = 16·13 ± 0·40. At this temperature k1 is independent of [IrCl63-]0 (1 and 5mF), of [H+] (103--1·0 M) and of μ (up to 0·04 M). Cl- anation of Ir(H2O)Cl52- 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{ina}-1=28·24 ± 1·03 Kcal mole-1, log PZ = 14·81 ± 0·71}. At this temperature, k-1′ conforms equation k′=ka[Cl-]/( kb kc+[Cl-]) where ka=0·382×10-5 and kb kc=1·85 M. At same temperature and μ=1·030 M, K=12 M. The rate constant for aquation of Ir(H2O)Cl52- is k2=(0·119±0·003)×10-5 sec-1 at 25°C in 0·1 M HClO4 (μ=0·130 M). © 1969.