Hydrogen Peroxide in the Chemistry of f-Elements

Abstract

The properties of H₂O₂ and its reactions with lanthanide and actinide ions are considered. The potential values of pairs involving H₂O₂ in acidic and alkaline solutions are given. Depending on the oxidative potential of the f-element ion and pH, H₂O₂ exhibits oxidizing or reducing properties. The kinetics and mechanisms of reactions of H₂O₂ with lanthanides(II–IV) and with actinides(III–VII) in acidic, carbonate, and alkaline media have been analyzed. Ions of f-elements(III–VI) form peroxide complexes. The peroxo group occupies either one (OOH) or two (OO) coordination sites. U(VI), Np(IV) binds up to 3 peroxo groups. Oxidation or reduction reactions proceed intramolecularly. In the case of Yb²⁺, Sm²⁺, U³⁺, Ce⁴⁺ (in an acid solution), Pr(IV) and Am(IV) (in a weakly acidic medium), the bimolecular rate constants are 10⁵–n × 10⁶ L/(mol s), which exceeds the rate of ligand exchange in the coordination sphere of the f-element ion. Therefore, charge transfer occurs in the outer sphere. Coordination spheres of Ce(IV) oxalate, Tb(IV) with P₂W₁₇O₆₁^10–, and Np(VI) with NO₃^– slow down the charge transfer between H₂O₂ and the f-element ion. H₂O₂ arising during the radiolysis of aqueous solutions is in an excited state and is more active than H₂O₂ introduced from the outside. Of particular interest are the reactions of H₂O₂ with ions of f-elements in strongly complexing or nonaqueous (organic) media, as well as structural studies of solid compounds of peroxides of f-elements.