Catalysis by dodeca-µ-chloro-octahedro-hexatantalum (3+) ion of the oxidation of tin(II) by iron(III) in aqueous solution

Abstract

Rate constants have been obtained for the reaction Fe³⁺+[Ta₆Cl₁₂]³⁺→ Fe²⁺+[Ta₆Cl₁₂]⁴⁺ and its reverse, and for the reduction of [Ta₆Cl₁₂]³⁺ and of [Ta₆Cl₁₂]⁴⁺ by Sn²⁺. The results make possible an interpretation of the catalysis of the reaction 2Fe³⁺+ Sn²⁺→ 2Fe²⁺+ Sn^IV by [Ta₆Cl₁₂]³⁺ in aqueous solutions at 25 °C, [H⁺]= 0.50 mol dm^–3, [Cl^–]≈ 0.04 mol dm^–3, and I= 1.1 mol dm^–3(Na[ClO₄]). The dominant path of catalysis at low iron(II) concentrations is as in (i)–(iii). At higher iron (II) concentrations there is a proportionately greater contribution from other reactions, including (iV) and (v). Fe³⁺+[Ta₆Cl₁₂]³⁺⇌ Fe²⁺+[Ta₆Cl₁₂]⁴⁺(i), [Ta₆Cl₁₂]⁴⁺+ Sn²⁺→[Ta₆Cl₁₂]³⁺+ Sn^III [graphic omitted] [Ta₆Cl₁₂]²⁺+ Sn^IV(II), Fe³⁺(or [Ta₆Cl₁₂]⁴⁺)+[Ta₆Cl₁₂]²⁺ [graphic omitted] Fe²⁺(or [Ta₆Cl₁₂]³⁺)+[Ta₆Cl₁₂]³⁺(iii), [Ta₆Cl₁₂]³⁺+ Sn²⁺→[Ta₆Cl₁₂]²⁺+ Sn^III(iv), Fe³⁺(or [Ta₆Cl₁₂]³⁺)+ Sn^III [graphic omitted] Fe²⁺(or [Ta₆Cl₁₂]²⁺)+ Sn^IV(v)