Journal
INORGANIC CHEMISTRY
Volume 56, Issue 3, Pages 1722-1733Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.inorgchem.6b02897
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Funding
- U.S. Department of Energy, Office of Nuclear Energy, DOE Idaho Operations Office [DE-AC07-05ID14517]
- Fuel Cycle Research and Development Program, Office of Nuclear Energy, U.S. Department of Energy
- Office of Science of the U.S. Department of Energy [DE-AC02-05CH11231, DE-AC05-00OR22725]
- Grants-in-Aid for Scientific Research [14J00202, 16K18351] Funding Source: KAKEN
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Potentiometric and spectroscopic techniques were combined with DFT calculations to probe the coordination environment and determine thermodynamic features of trivalent f-element complexation by N-hydroxyethyl-diethylenetriamine-N,N',N '',N ''-tetraacetic acid, HEDTTA. Ligand protonation constants and lanthanide stability constants were determined using potentiometry. Five protonation constants were accessible in I = 2.0 M (H+/Na+)ClO4. UV-vis spectroscopy was used to determine stability constants for Nd3+ and Am3+ complexation with HEDTTA. Luminescence spectroscopy indicates two water molecules in the inner coordination sphere of the Eu/HEDTTA complex, suggesting HEDTTA is heptadentate. Luminescence data was supported by DFT calculations, which demonstrate that substitution of the acetate pendant arm by a N-hydroxyethyl group weakens the metal nitrogen bond. This bond elongation is reflected in HEDTTA's ability to differentiate trivalent actinides from trivalent lanthanides. The trans-lanthanide Ln/HEDTTA complex stability trend is analogous to Ln/DTPA complexation; however, the loss of one chelate ring resulting from structural substitution weakens the complexation by similar to 3 orders of magnitude. Successful separation of trivalent americium from trivalent lanthanides was demonstrated when HEDTTA was utilized as aqueous holdback complexant in a liquid liquid system. Time-dependent extraction studies for HEDTTA were compared to diethylenetriamine-N,N,N',N '',N ''-pentaacetic acid (DTPA) and N-hydroxyethyl-ethylenediamine-N,N',Ni-triacetic acid (HEDTA). The results indicate substantially enhanced phase-transfer kinetic rates for mixtures containing HEDTTA.
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