Crystallization of Tri- and Tetravalent Plutonium Diglycolamides

Used nuclear fuel (UNF) creates a significant obstacle when it comes to the widespread adoption of nuclear power. Over time, transuranic and lanthanide fission products accumulate, the latter of which are neutron poisons that reduce the efficiency of nuclear fuel. From here, the UNF must be recycled/reprocessed to remove these problematic isotopes. Of particular interest is the separation of minor actinides (Am, Cm, and Np) from the UNF as they are very long lived and responsible for the majority of the heat and radiotoxic burden of UNF. Many proposed strategies for separating the minor actinides employ liquid-liquid extraction methods that utilize chelating ligands to preferentially complex the minor actinides over the lanthanides. One such proposed class of chelating ligands are the diglycolamides (DGA). These ligands have shown great promise due to their high affinity towards the trivalent transuranic elements, particularly that of americium and curium. Additionally, DGAs fall under the CHON doctrine, where the ligand only consists of carbon, hydrogen, oxygen, and nitrogen, thereby reducing the level of waste generated as compared to methods utilizing phosphorus and sulphur-based extractants. However, these separation processes are subject to intense, multicomponent radiation fields which results radiolytic reactions in these environments to produce transient tetravalent actinide species. Understanding the interactions between these transient species and DGAs is vital. In this study, plutonium was crystallized with the hydrophilic tetramethyl diglycolamide (TMDGA) and characterized by single-crystal X-ray crystallography. Homoleptic crystalline products were produced containing plutonium(III) and plutonium(IV), providing an opportunity to study subtle differences across oxidation states in the same compound. Geometry calculations were also performed on the coordinating oxygens atoms and the solid-state absorption spectra were analysed and compared to similar plutonium structures. (authors)