Abstract
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 ∼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′,N′-triacetic acid (HEDTA). The results indicate substantially enhanced phase-transfer kinetic rates for mixtures containing HEDTTA.
| Original language | English |
|---|---|
| Pages (from-to) | 1722-1733 |
| Number of pages | 12 |
| Journal | Inorganic Chemistry |
| Volume | 56 |
| Issue number | 3 |
| DOIs | |
| State | Published - Feb 6 2017 |
Funding
The experimental work conducted by T.S.G., C.R.H., M.N., and P.R.Z. at the Idaho National Laboratory was supported by the U.S. Department of Energy, Office of Nuclear Energy, DOE Idaho Operations Office, under contract DE-AC07-05ID14517. The synthetic work by S.J.-P. and computational studies by V.S.B. and S.G.S. were supported by the Fuel Cycle Research and Development Program, Office of Nuclear Energy, U.S. Department of Energy. DFT calculations used resources of the National Energy Research Scientific Computing Center and the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, both of which are supported by the Office of Science of the U.S. Department of Energy under contract nos. DE-AC02- 05CH11231 and DE-AC05-00OR22725, respectively.
| Funders | Funder number |
|---|---|
| DOE Idaho Operations Office | DE-AC07-05ID14517 |
| Fuel Cycle Research and Development Program | |
| U.S. Department of Energy | |
| Office of Science | DE-AC05-00OR22725, DE-AC02- 05CH11231 |
| Office of Nuclear Energy | |
| Oak Ridge National Laboratory | |
| Japan Society for the Promotion of Science | 16K18351, 14J00202 |