Complexes of Hydrogen Peroxide with Dioxoactinide(VI) Species in Aqueous Carbonate and Bicarbonate Media. Formation of An(VI)–H2O2 Complexes

The spectra for 1:1 complexes formed between triscarbonatouranium(VI) + H2O2 and triscarbanatoneptunium(VI) + H2O2 are presented. The respective rates of formation (25°C, 0.05 M NA2CO3) are 565 ± 41 M−1 s−1 and (2.19 ± .01) X 103 M−1 s−1. The corresponding activation parameters are ΔH* = 67.8 ± 3.2 kJ/m, 43.6 ± 2.0 kJ/m, ΔS* = 30 ± 11 J/m °K and −36 ± 7 J/m °K, respectively. The U(VI) complex appears to be stable over a period of months while the Np(VI) complex is formed as a transient species that disappears via a complex process.