Highly efficient separation of actinides from lanthanides by a phenanthroline-derived bis-triazine ligand

The synthesis, lanthanide complexation, and solvent ex- traction of actinide(III) and lanthanide(III) radiotracers from nitric acid solutions by a phenanthroline-derived quadridentate bis-triazine ligand are described. The ligand separates Am(III) and Cm(III) from the lanthanides with remarkably high efficiency, high selectivity, and fast extraction kinetics compared to its 2,2'-bipyridine counterpart. Structures of the 1:2 bis-complexes of the ligand with Eu(III) and Yb(III) were elucidated by X-ray crystallography and force field calculations, respec-tively. The Eu(III) bis-complex is the first 1:2 bis-complex of a quadridentate bis-triazine ligand to be characterized by crystallography. The faster rates of extraction were verified by kinetics measurements using the rotating membrane cell technique in several diluents. The improved kinetics of metal ion extraction are related to the higher surface activity of the ligand at the phase interface. The improvement in the ligand's properties on replacing the bipyridine unit with a phenanthroline unit far exceeds what was anticipated based on ligand design alone

Interaction of 6,6′′-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2′:6′,2′′-terpyridine (CyMe4-BTTP) with some trivalent ions such as lanthanide(iii) ions and americium(iii)

The new ligand 6,6 ''-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)2,2':6 ',2 ''-terpyridine (CyMe4-BTTP) has been synthesized in 4 steps from 2,2':6',2 ''-terpyridine. Detailed NMR and mass spectrometry studies indicate that the ligand forms 1 : 2 complexes with lanthanide(III) perchlorates where the aliphatic rings are conformationally constrained whereas 1 : 1 complexes are formed with lanthanide(III) nitrates where the rings are conformationally mobile. An optimized structure of the 1 : 2 solution complex with Yb(III) was obtained from the relative magnitude of the induced paramagnetic shifts. X-Ray crystallographic structures of the ligand and of its 1 : 1 complex with Y(III) were also obtained. The NMR and mass spectra of [Pd(CyMe4-BTTP)](n)(2n+) are consistent with a dinuclear double helical structure (n = 2). In the absence of a phase-modifier, CyMe4-BTTP in n-octanol showed a maximum distribution coefficient of Am(III) of 0.039 (+/-20%) and a maximum separation factor of Am(III) over Eu(III) of 12.0 from nitric acid. The metal(III) cations are extracted as the 1 : 1 complex from nitric acid. The generally low distribution coefficients observed compared with the BTBPs arise because the 1 : 1 complex of CyMe4-BTTP is considerably less hydrophobic than the 1 : 2 complexes formed by the BTBPs. In M(BTTP)(3+) complexes, there is a competition between the nitrate ions and the ligand for the complexation of the metal

Applications of Nuclear Magnetic Resonance to actinide chemistry and nuclear waste reprocessing.

This research work is dedicated to develop and bring to light the contribution of nuclear magnetic resonance (NMR) in the study of the actinide ions and their complexes in aqueous or in organic solvents. We use several advanced NMR techniques. The dispersion of the longitudinal relaxation time T1 of solvent nuclei with the magnetic field (NMRD) yields information on the magnetic properties of paramagnetic actinide ions. The sensitivity of NMR to the exact nature of the ground state of actinide ions is also illustrated by detailed studies on the complexes of U, Np, Pu, Am and Cm in different oxidation states. It will be shown that the paramagnetic shifts induced by the actinide ions originate from both a through space dipolar contribution and a through bonds contact contribution. The latter gives access to delocalized unpaired electron densities that are directly related to the covalency of the actinide-ligand bonds. However, electronic densities can only be obtained after separation of the two contributions. This separation made thanks three different methods based on studies with variable temperature and by synthesizing highly symmetric and anisotropic complexes. The use of dipolar contribution can be, as for her, related to the geometry of complexes formed in solution. This method of determination of solution structure is illustrated in the case of four specially designed N-polyaromatic ligands actinide/lanthanide partitioning by liquid-liquid extraction, an essential step for the ultimate nuclear fuel reprocessing. Besides their structure determination, the use of NMR techniques allowed of determined the stoechiometry and speciation in solution of these complexes.Ce travail de recherche est consacré à développer et mettre en évidence l’apport de la résonance magnétique nucléaire (RMN) dans l’étude des ions actinide et de leurs complexes en milieu aqueux ou organique. L’emploi de plusieurs techniques RMN est ainsi utilisé. La dispersion du temps de relaxation longitudinal T1 des molécules de solvants avec le champ magnétique fournit d’importantes informations sur les propriétés magnétiques des ions actinides paramagnétiques. La sensibilité de la RMN à la nature exacte de l’état fondamental des ions actinides est mise en évidence au moyen d’études détaillées de complexes de U, Np, Pu, Am et Cm dans différents états d’oxydation. Il est montré que les déplacements paramagnétiques induits par les actinides sont dus à une interaction dipolaire à travers l’espace et à une contribution de contact transmise par les liaisons. Cette dernière contribution donne directement accès à la délocalisation de la densité d’électrons non appariés liée à la covalence des liaisons actinide-ligand. Cependant, cette densité électronique ne peut être obtenue qu’après séparation des deux contributions. Celle-ci a été effectuée au moyen de trois méthodes différentes basées sur des études à température variable et en synthétisant des complexes hautement symétriques et anisotropes. L’emploi de la contribution dipolaire du déplacement paramagnétique peut quant à elle être reliée à la géométrie des complexes formés en solution. Cette méthode de détermination de la structure tridimensionnelle des complexes est illustrée par l’étude de quatre ligands N-polyaromatiques spécialement élaborés pour séparer les actinides des lanthanides par extraction liquide-liquide, étape essentielle dans le retraitement ultime des combustibles nucléaires. Outre la détermination de leur structure, l’emploi des techniques RMN a permis de déterminer la stœchiométrie et la spéciation de ces complexes en solution

Développements récents dans l’élaboration de composés radiopharmaceutiques au 99mTc.

Nouveaux développements dans la production de radio-pharmaceutiques au 99mTc et mise en perspective de l'apport de la chimie dans ce domaine

The NMR techniques: a powerful method to study solution structure of new agents for actinides/lanthanides extraction

audience: researcher, studen

AN NMR INVESTIGATION OF THE ACTINIDE IONS AND THEIR COMPLEXES

We currently use several advanced NMR techniques in order to fully characterize actinide ions and their complexes in water or in organic solvents. The dispersion of the longitudinal relaxation time T1 of solvent nuclei with the magnetic field (NMRD) yields information on the magnetic properties and on the dynamic behavior of paramagnetic species. 17O NMR allows the measurement of the water exchange times and 1H and 13C spectra yield information on the solution structures of the complexes and on the covalency of their coordination bonds. The application of NMR in actinide science will be illustrated with studies on the U, Np, Pu and Cm ions in different oxidation states and on their complexes. For instance, Cm3+ ion is the actinide analogue of Gd3+ but is not in a pure 8S state as indicated by much lower relaxation rates and much shortened electronic relaxation rates. In keeping with EPR studies1, Cm3+ does not have a perfectly spherical distribution of its unpaired electronic spins because of a much stronger spin-orbit coupling. Moreover, the Cm3+ relaxivity originates from three different processes: a dipolar coupling between the nuclear and electronic spins, a delocalization of unpaired electronic spins into the solvent orbitals (contact interaction) and a Curie contribution. Each process gives rise to an inflection point in the NMRD curves and the contact interaction reflects the partial covalency of the coordination bonds formed by Cm3+. A contact contribution is also observed in the NMR spectra of Cm3+ complexes. The sensitivity of NMR to the exact nature of the ground state of actinide ions is also illustrated by detailed studies on the U, Np and Pu ions in different oxidation states. For instance, a comparison of the NMRD curves of the 5f2 ions U4+, NpO2+ and PuO22+ indicates that the two dioxo cations have abnormally long electronic relaxation times. However, well-resolved 1H NMR spectra of their complexes can be obtained provided the solution species are sufficiently rigid. It will be shown that NpO2+ and PuO22+ induce dipolar paramagnetic shifts from which the solution structure can be deduced

NMR studies on radioactive actinide complexes. A completely foolish idea?

The complete separation of actinides and lanthanides by solvent extraction is an important step in the reprocessing of nuclear wastes. The trivalent ions of these two families of f elements have very similar properties and it is only recently that an effective separation method has been developed. It is assumed that this separation can be achieved because of small differences in the covalency of the coordination bonds formed by the f ions but this has not been proved so far. We embarked into the first NMR study of the actinide complexes with the hope of better unravelling their solution structures and of clarifying the role of covalency. Nuclear magnetic resonance has nearly never been used for investigating actinide ions and their complexes not only because of their radioactivity and their toxicity but also because of the lack of dedicated spectrometers. It was also assumed that paramagnetism would cause excessive line broadenings. Many difficulties had thus to be overcome and the first step in our work was to show that well-resolved NMR spectra of actinide complexes (U to Cm) could indeed be obtained. Relatively narrow resonances have been observed for a variety of ions in different oxidation states provided their complexes are stable, symmetric and rigid. We used several advanced NMR techniques in order to fully characterize the actinide ions and their chelates in water or in organic solvents. The dispersion of the longitudinal relaxation time T1 of solvent nuclei with the magnetic field (NMRD) yields information on the magnetic properties and on the dynamic behaviour of paramagnetic species; 17O NMR allows the measurement of the water exchange times and 1H and 13C spectra yield information on the solution structures of the complexes. It will be shown that the paramagnetic shifts induced by the actinide ions originate from both a through space dipolar contribution and a through bonds contact contribution. The latter gives access to delocalized unpaired electron densities that are directly related to the covalency of the metal-ligand bonds. However, electron densities can only be obtained after separation of the two contributions. This could be accomplished thanks to variable temperature studies. In another approach, new ligands with rigid aliphatic substituents have been synthesized and contact contribution were deduced with the assumption that delocalization does not proceed to the 1H nuclei most removed from the metal center. This study has been extended to actinides in the trivalent, tetravalent and hexavalent states and new ligands have been synthesized in order to increase the magnetic anisotropy while keeping the symmetry and the rigidity needed to simplify the NMR analyses

Nuclear magnetic resonance applied to actinide ions and their complexes. In search of covalency effects

ACSPE

Nuclear Magnetic Resonance and Nuclear Waste Reprocessing.

audience: researcher, studen