Influence of a Heterocyclic Nitrogen-Donor Group on the Coordination of Trivalent Actinides and Lanthanides by Aminopolycarboxylate Complexants
- Idaho National Lab. (INL), Idaho Falls, ID (United States)
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Here, the novel metal chelator – N-2-pyridylmethyl-diethylenetriamine-N,N',N'',N''-tetraacetic acid, DTTA-PyM – was designed to replace a single O-donor acetate group of the well-known aminopolycarboxylate complexant diethylenetriamine-N,N,N',N'',N''-pentaacetic acid (DTPA) with an N-donor 2-pyridylmethyl. Potentiometric, spectroscopic, computational, and radioisotope distribution methods show distinct differences for the 4f and 5f coordination environments and enhanced actinide binding due to the nitrogen bearing heterocyclic moiety. The Am3+, Cm3+, Ln3+ complexation studies for DTTA-PyM reveal an enhanced preference, relative to DTPA, for trivalent actinide binding. Fluorescence studies indicate no changes to the octadentate coordination of trivalent curium, while evidence of heptadentate complexation of trivalent europium is found in mixtures containing EuHL(aq) complexes at the same aqueous acidity. The denticity change observed for Eu3+ suggests that complex protonation occurs on the pyridyl nitrogen. Formation of the CmHL(aq) complex is likely due to the protonation of an available carboxylate group since the carbonyl oxygen can maintain octadentate coordination through a rotation. The observed suppressed protonation of the pyridyl nitrogen in the Cm complexes may be attributed to stronger trivalent actinide binding by DTTA-PyM. Density functional theory calculations indicate that added stabilization of the actinide complexes with DTTA-PyM may originate from p back-bonding interactions between singly occupied 5f orbitals of Am3+ and the pyridyl nitrogen. The differences between the stability of trivalent actinide chelates (Am3+, Cm3+) and trivalent lanthanide chelates (La3+-Lu3+) are observed in liquid-liquid extraction systems, yielding unprecedented 4f/5f differentiation when using DTTA-PyM as an aqueous holdback reagent. In addition, the enhanced N-donor softness of the new DTTA-PyM chelator was perturbed by adding a fluorine onto the pyridine group. The comparative characterization of N-(3-fluoro-2-pyridylmethyl)-diethylenetriamine-N,N',N'',N''-tetraacetic acid, DTTA-3-F-PyM, showed subdued 4f/5f differentiation due to the presence of this electron-withdrawing group.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Idaho National Lab. (INL), Idaho Falls, ID (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); USDOE Office of Nuclear Energy (NE)
- Grant/Contract Number:
- AC07-05ID14517
- OSTI ID:
- 1477508
- Report Number(s):
- INL/JOU-17-43766-Rev000
- Journal Information:
- Inorganic Chemistry, Vol. 57, Issue 3; ISSN 0020-1669
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Origin of Selectivity of a Triazinyl Ligand for Americium(III) over Neodymium(III)
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journal | February 2019 |
Pyridine Polyaminocarboxylate Ligands for Use as Actinide-selective Holdback Reagents in Simplified TALSPEAK-like Extraction Systems
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journal | March 2020 |
Pyridine Polyaminocarboxylate Ligands for Use as Actinide-selective Holdback Reagents in Simplified TALSPEAK-like Extraction Systems
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text | January 2020 |
Pyridine Polyaminocarboxylate Ligands for Use as Actinide-selective Holdback Reagents in Simplified TALSPEAK-like Extraction Systems
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text | January 2020 |
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