The hydrolysis of iridium(III)

Abstract

The hydrolysis of aquairidium(III) has been investigated at 5, 15, 25, and 35 °C in aqueous solutions of constant [ClO₄]^– molality (1.05 mol kg^–1). A series of gravimetric titrations has been performed and the pH followed potentiometrically using hydrogen electrodes. The measurements are fully reversible even in the heterogeneous range and can be explained assuming the following equilibria: [Ir(OH₂)₆]³⁺⇌[Ir(OH₂)₅(OH)]²⁺+ H⁺; *K₁=[Ir(OH)][H⁺][Ir]^–1, [Ir(OH₂)₅(OH)]²⁺⇌[Ir(OH₂)₄(OH)₂]⁺+ H⁺; *K₂=[Ir(OH)₂][H⁺][Ir(OH)]^–1, [Ir(OH₂)₃(OH)₃](s)+ 3H⁺⇌[Ir(OH₂)₆]³⁺; *K₈₀=[Ir][H⁺]^–3

The individual equilibrium constants (using the molality scale) obtained at 25 °C (errors 1σ) are log *K₁=–4.37 ± 0.02, log *K₂=–5.20 ± 0.15, and log *K₈₀= 10.22 ± 0.05. These results are compared with general predictions for the hydrolysis behaviour of aqua-cations.