Influence of the Redox Potential and Charge of f Element Ions on the Kinetics of Reactions Involving Them

Аннотация

Experimental data on the kinetics of reactions of lanthanide and actinide ions with ОН radicals, e_aq^–, each other, and d element ions are analyzed. The reactions with ОН radicals are kinetically controlled, with the rate constants being independent of the redox potential of the ion. This is due to the fact that the ОН radical abstracts the H atom from Н₂О in the hydration shell, which is followed by the charge transfer. The An⁴⁺ ions are oxidized with the formation of the An⁵⁺ ions, followed by their hydrolysis. The hydrated electrons e_aq^– react with f element ions whose potential is less negative than–2.0 V, with the reaction being diffusion-controlled. The reactions of e_aq^– with An⁴⁺ and AnO₂²⁺ occur by the tunneling mechanism. The reactions of the ions with each other are kinetically controlled, with the rate constants depending on ΔЕ of the reaction. The correlation is broken in the case of formation of AnO₂⁺–An⁴⁺ cation–cation complexes or of reactions involving the structure rearrangement. The stability of heptavalent ions in an alkaline solution decreases with an increase in the oxidation potential and with a decrease in the ion charge.