Synthesis and structure of Americium(III) diglycolate oxalate Trihydrate, Am(ODA)(C2O4)(H2O)3

Abstract

Improving f-element separations is important for actinide(III) (An3+) and lanthanide(III) (Ln3+) based technologies. Unfortunately, An3+ and Ln3+ ions are difficult to separate from one another because they have similar chemical characteristics. One successful separation method utilizes anion exchange chromatography. This approach exploits differences in An3+ and Ln3+ Lewis acidities and their varying abilities to attract anionic complexing agents, like oxalates (C2O42–) and diglycolates (ODA2–). The resulting negatively charged complexes are then separated using an anion exchange resin. To better understand how this anion exchange separation works, we reacted Am3+(aq) (aq designates Am3+ dissolved in water) with the anion exchange complexing agents (H2C2O4 and H2ODA). The resulting Am(ODA)(C2O4)(H2O)3 product was characterized using single crystal X-ray diffraction and UV-Vis-NIR spectroscopy. The Am(ODA)(C2O4)(H2O)3 structure was similar to that established previously for Ln3+ analogues, namely Ln(ODA)(C2O4)(H2O)x. These compounds were all isomorphous, had bridging C2O42– and ODA2– ligands, and crystallized as 2-dimensional extended solids. In addition, the Am3+–O bond distances could be predicted based on relative differences in Am3+ and Ln3+ 9-coordinate metal ionic radii. Overall, isolation of Am(ODA)(C2O4)(H2O)3 showcased similarities in complexation and crystallization chemistry for Am3+ and Ln3+.