Complexation of An( vi ) with succinic acid in aqueous acid solutions: uranyl vs. plutonyl

The complexation of U( vi ) and Pu( vi ) with succinic acid in aqueous acid solutions is investigated and compared. Affinity capillary electrophoresis (ACE) has been used to study the interaction of U( vi ) with succinic acid in perchloric acid aqueous solutions ( p [H] 2.0–2.5, 0.1 M ionic strength). The speciation model for uranyl is deduced in the presence of succinic acid. The existence of protonated complexes UO 2 HSuc + and UO 2 (HSuc) 2 is supposed and the stability constant values for these complex species are calculated. The interaction of Pu( vi ) with succinic acid has been investigated using UV-vis spectrophotometry. The equilibria with the formation of PuO 2 (HSuc) 2 , PuO 2 HSuc 2 − and PuO 2 (Suc) 2 2− complex species are found. The stability constant values are calculated at 0.1 M and 1 M ionic strengths. The existence of UO 2 (HSuc) 2 , PuO 2 (HSuc) 2 and PuO 2 HSuc 2 − is suggested for the first time. It is noticed that the complex species of U( vi ) with succinic acid are more stable than the ones of Pu( vi ). The U( vi ) and Pu( vi ) systems with succinic acid are also investigated using density functional theory (DFT). It is observed that actinyl has a bidentate coordination with a succinate anion. Using DFT calculations the experimental finding that uranyl–succinate species are more stable than the corresponding plutonyl–succinate ones is confirmed. This trend in stability is explained by a stronger electrostatic interaction in the uranyl–succinate complexes.