Complex formation reaction of the iron(iii) hydroxo dimer with periodate ion

Abstract

The kinetics and mechanism of the ligand substitution reaction between Fe₂(OH)₂⁴⁺ and periodate ion has been studied. This process is unique among the reactions of the iron(III) hydroxo dimer because the initial rate is second-order with respect to Fe₂(OH)₂⁴⁺. The formation of a bi- and a tetranuclear complex, Fe₂(OH)₂(H₄IO₆)³⁺ and Fe₄(OH)₄(H₄IO₆)⁷⁺, is proposed. Comprehensive fitting of the kinetic data was used to show that the proposed model, which is very similar to earlier models used with other inorganic oxoanions, gives a reasonable interpretation of all observations. It is shown that the lifetime of Fe₂(OH)₂(H₄IO₆)³⁺ is relatively long and it can open a pathway to form oligomeric and less soluble products at higher initial concentrations. The speciation of aqueous periodate ion solution was also studied and it is proposed that the tetrahedral form, IO₄⁻, is less dominant over the octahedral form, H₄IO₆⁻, than previously thought.