Unpublished conference/Abstract (Scientific congresses and symposiums)
NMR studies on radioactive actinide complexes. A completely foolish idea?
Vidick, Geoffrey; Bouslimani, Nouri; Desreux, Jean-François
2010ninth One-day Symposium of Young Belgian Magnetic Resonance Scientists
 

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Keywords :
NMR; Actinide; paramagnetisme
Abstract :
[en] 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.
Disciplines :
Chemistry
Author, co-author :
Vidick, Geoffrey ;  Université de Liège - ULiège > Centre de recherches du cyclotron
Bouslimani, Nouri
Desreux, Jean-François ;  Université de Liège - ULiège > Département de chimie (sciences) > Département de chimie (sciences)
Language :
English
Title :
NMR studies on radioactive actinide complexes. A completely foolish idea?
Publication date :
26 November 2010
Number of pages :
29
Event name :
ninth One-day Symposium of Young Belgian Magnetic Resonance Scientists
Event organizer :
F.N.R.S.
Event place :
Bruxelles, Belgium
Event date :
26 novembre 2010
Available on ORBi :
since 14 February 2012

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