Liquid-liquid extractions are used in nuclear waste reprocessing, to separate the actinides from the shorter-lived fission products. High binding affinities are necessary to selectively extract the actinide from the mixture and tetrahydrofuran-2,3,4,5-tetracarboxylic acid (THFTCA) is an effective ligand in separating uranium from other lanthanides and actinides1 present in the waste stream. In this study, we explore the selective crystallizations of actinide-THFTCA complexes to understand binding modes and affinities. Heterometallic solutions containing either UO2-Cu, UO2-Sr, La-Cu, Sr-Cu, or Ce-Cu yielded homometallic crystalline materials. In total, three novel structures containing THFTCA and either the uranyl(VI) or copper(II) cation were synthesized and characterized with single crystal X-ray diffraction, powder X-ray diffraction and Raman spectroscopy. Compound 1 ((C4H10N2)[UO2(C8H8O9)2] 2H2O) is a molecular monomer with piperazinium acting as a charge balancing counter-cation. Compound 2 (Na[(UO2)2(C8H8O9)OH] 2H2O) contained a 3D framework assembled via electrostatic interactions with Na+ cations, whereas 3 (Cu(C10H8N2)(C8H8O9)) formed 1D chains that were further linked through π-π stacking. The solid-state Raman shows vibrational differences in bands associated with the THFTCA upon coordination. Solution-state Raman was used to evaluate 1, 2, and 3 over time to identify how the vibrational modes changed over the crystallization period. Further, isothermal titration calorimetry was used to determine the binding constants for uranyl and copper to THFTCA in solution and evaluate the selectivity of the complexes synthesized from the heterometal systems.

Exploring actinide complexes with tetrahydrofuran-2,3,4,5-tetracarboxylic acid

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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