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Research article - Peer-reviewed, 2015

The structures of CyMe4-BTBP complexes of americium(III) and europium(III) in solvents used in solvent extraction, explaining their separation properties

Ekberg, Christian; Löfström-Engdahl, Elin; Aneheim, Emma; Foreman, Mark R. StJ.; Geist, Andreas; Lundberg, Daniel; Denecke, Melissa; Persson, Ingmar;

Abstract

Separation of trivalent actinoid (An(III)) and lanthanoid (Ln(III)) ions is extremely challenging due to their similar ionic radii and chemical properties. Poly-aromatic nitrogen compounds acting as tetradentate chelating ligands to the metal ions in the extraction, have the ability to sufficiently separate An(III) from Ln(III). One of these compounds, 6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzol[1,2,4]triazin-3-yl)-[2,2]bipyridine, CyMe4-BTBP, has proven to be resistant towards acidic environments and strong radiation from radioactive decomposition. EXAFS studies of the dicomplexes of CyMe4-BTBP with americium(III) and europium(III) in nitrobenzene, cyclohexanone, 1-hexanol, 1-octanol and malonamide (DMDOHEMA) in 1-octanol have been carried out to get a deeper understanding of the parameters responsible for the separation. The predominating complexes independent of solvent used are [Am(CyMe4-BTBP)(2)(NO3)](2+) and [Eu(CyMe4-BTBP)(2)](3+), respectively, which are present as outer-sphere ion-pairs with nitrate ions in the studied solvents with low relative permittivity. The presence of a nitrate ion in the first coordination sphere of the americium(III) complex compensates the charge density of the complex considerably in comparison when only outer-sphere ion-pairs are formed as for the [Eu(CyMe4-BTBP)(2)](3+) complex. The stability and solubility of a complex in a solvent with low relative permittivity increase with decreasing charge density. The [Am(CyMe4-BTBP)(2)(NO3)](2+) complex will therefore be increasingly soluble and stabilized over the [Eu(CyMe4-BTBP)(2)](3+) complex in solvents with decreasing relative permittivity of the solvent. The separation of americium(III) from europium(III) with CyMe4-BTBP as extraction agent will increase with decreasing relative permittivity of the solvent, and thereby also with decreasing solubility of CyMe4-BTBP. The choice of solvent is therefore a balance of a high separation factor and sufficient solubility of the CyMe4-BTBP ligand.

Keywords

Solvent extraction, americium, europium, structure determination, organic solvents

Published in

Dalton Transactions

2015, volume: 44, number: 42, pages: 18395-18402

Authors' information

Ekberg, Christian
Chalmers University of Technology
Löfström-Engdahl, Elin
Chalmers University of Technology
Aneheim, Emma
Chalmers University of Technology
Foreman, Mark R. StJ.
Chalmers University of Technology
Geist, Andreas
Karlsruhe Institute of Technology
Lundberg, Daniel
Swedish University of Agricultural Sciences, The Department of Chemistry and Biotechnology
Denecke, Melissa
University of Manchester
Swedish University of Agricultural Sciences, Department of Chemistry

UKÄ Subject classification

Inorganic Chemistry

Publication Identifiers

DOI: https://doi.org/10.1039/c5dt02859k

URI (permanent link to this page)

https://res.slu.se/id/publ/71845