Abstract
The trivalent f-element coordination chemistry of a novel aminopolycarboxylate complexant was investigated. The novel reagent is an octadentate complexant that resembles diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA), but a single N-acetate pendant arm was substituted with a N-2-pyrazinylmethyl functional group. Thermodynamic studies of ligand protonation and trivalent lanthanide, americium and curium, complexation by N-2-pyrazinylmethyldiethylenetriamine-N,N′,N″,N″-tetraacetic acid (DTTA-PzM) emphasize the strong electron withdrawing influence of the N-2-pyrazinylmethyl group. Specifically, DTTA-PzM is more acidic compared to a N-2-pyridinylmethyl-substituted structural equivalent, DTTA-PyM, with a substantial lowering of pK7, corresponding to the protonation of a second aliphatic amine site. The participation of the pyrizyl nitrogen in the metal ion coordination sphere is evident from the fluorescence lifetime decay measurements of metal hydration and the interpretation of the stability constants for ML- and MHL(aq) complexes. The overall conditional stability constants for the trivalent f-element complexation by DTTA-PzM complexes decrease, relative to DTTA-PyM, as expected based on the lower basicity of pyrazine in water relative to pyridine. Replacement of the N-2-pyridinylmethyl group with N-2-pyrazinylmethyl, while enhancing the total acidity of DTTA-PzM, also reduces its softness, as manifested by a small lowering of β101Am/Nd and liquid-liquid separation of trivalent lanthanides from trivalent americium. Despite this, the 4f/5f separation is doubled when DTTA-PzM replaces DTPA as an aqueous complexant in solvent extraction.
Original language | English |
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Pages (from-to) | 138-150 |
Number of pages | 13 |
Journal | Inorganic Chemistry |
Volume | 59 |
Issue number | 1 |
DOIs | |
State | Published - Jan 6 2020 |
Funding
This work was supported by the Fuel Cycle Research and Development Program, Office of Nuclear Energy, U.S. Department of Energy. The experimental work conducted by T.S.G., C.R.H., and P.R.Z. at Idaho National Laboratory was performed under Contract DE-AC07-05ID14517. This research used resources of the National Energy Research Scientific Computing Center and the Computer and Data Environment for Science (CADES) at Oak Ridge National Laboratory, both of which are supported by the Office of Science, U.S. Department of Energy, under Contracts DE-AC02-05CH11231 and DE-AC05-00OR22725, respectively.
Funders | Funder number |
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Data Environment for Science | |
Fuel Cycle Research and Development Program | |
National Energy Research Scientific Computing Center | |
U.S. Department of Energy | |
Office of Science | DE-AC05-00OR22725, DE-AC02-05CH11231 |
Office of Nuclear Energy | |
Oak Ridge National Laboratory |