title: The structures of CyMe4-BTBP complexes of americium(iii) and europium(iii) in solvents used in solvent extraction, explaining their separation properties.
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.
authors.affiliation: Nuclear Chemistry/Industrial materials recycling, Chalmers University of Technology, SE-412 96 Göteborg, Sweden. che@chalmers.se.
authors.forename: Christian
authors.initials: C
authors.lastname: Ekberg
authors.forename: Elin
authors.initials: E
authors.lastname: Löfström-Engdahl
authors.forename: Emma
authors.initials: E
authors.lastname: Aneheim
authors.forename: Mark R StJ
authors.initials: MR
authors.lastname: Foreman
authors.forename: Andreas
authors.initials: A
authors.lastname: Geist
authors.forename: Daniel
authors.initials: D
authors.lastname: Lundberg
authors.forename: Melissa
authors.initials: M
authors.lastname: Denecke
authors.forename: Ingmar
authors.initials: I
authors.lastname: Persson
mesh_terms: D020003:1-Octanol / Q000737:chemistry; D000576:Americium / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D004553:Electric Conductivity; D005063:Europium / Q000737:chemistry*; D000441:Hexanols / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry
chemical_list: D056831:Coordination Complexes; D000441:Hexanols; D007477:Ions; D011725:Pyridines; D012997:Solvents; D005063:Europium; C036260:1-hexanol; D020003:1-Octanol; D000576:Americium