Inner to outer-sphere coordination of plutonium(IV) with N,N-dialkyl amide: influence of nitric acid

N,N-Dialkylamides are extensively studied as alternative organic ligands to achieve the extraction and separation of uranium(VI) and plutonium(IV). We report here the coordination structures of the plutonium(IV) ion with N,N-di(2-ethylhexyl)-n-butanamide as a function of nitric acid concentration in the aqueous phase. The coordination structure of Pu(IV) evolves gradually with increasing nitric acid concentration from an inner-sphere with two coordinated amide ligands toward an outer-sphere hexanitrate complex with only nitrate ions in the first coordination sphere and protonated amide ligands in the outer shell.