Kinetics of the rapid monomer–dimer equilibration of molybdenum(VI) in aqueous perchloric acid solutions

Abstract

The monomer–dimer equilibration of molybdenum(VI) in 0·2–3·0M perchloric acid solutions, I= 3·0M(LiClO₄), has been studied at 25 °C. Spectrophotometric measurements are consistent with the presence of a monomeric species, [HMoO₃]⁺, and dimeric species, [H₂Mo₂O₆]²⁺ and [H₃Mo₂O₆]³⁺, in agreement with previous work by Krumenacker. Evidence for the further monomeric species [H₂MoO₃]²⁺ has been obtained. Kinetic studies using the temperature-jump technique indicate a major pathway (i) for equilibration, with rate constant K₁=[HMoO₃]⁺+[HMoO₃]⁺ [graphic omitted] [H₂Mo₂O₆]²⁺(i)(1·71 ± 0·10)× 10⁵ l mol^–1s^–1 and k_–1=(3·20 ± 0·20)× 10³s^–1. The equilibration(ii), appears to contribute [H₂MoO₃]²⁺+[HMoO₃]⁺ [graphic omitted] [H₃Mo₂O₆]³⁺(ii) to a small extent with k₂=(0·3 ± 0·3)× 10⁵ l mol^–1s^–1 and k_–2=(30 ± 20) s^–1.