1. The NMR techniques: a powerful method to study solution structure of new agents for actinides/lanthanides extraction.
G.Vidick, J.F. Desreux
University of Liège, Coordination and Radiochemistry
INTRODUCTION
The gestion of nuclear waste remains a major challenge for futur generations, specially the stockage of high radiotoxic wastes.
The minor actinides [AM] (Am, Cm) represent to long time ( y) the principal contribution of waste radiotoxicity.
The transmutation of AM (transformation of nuclides to an other nuclides by particles bombardment) is going to allow of important
decrease of waste radiotoxicity, but require the separation of AM from neutrophage lanthanides [Ln].
The partitioning of AM from Ln is one of the biggest problem for chemists because the very similar properties of Ln and trivalent actinides.
U, Pu
Np, Tc, I
Fission Products + Cs Ln
Used Fuel
PUREX
DIAMEX
SANEX
An+Ln
Am+Cm
Stratégy for the Nuclear Fuel Cycle in th 21st Century.
A way for AM/Ln separation is the liq.-liq extraction. The 1,2,4-triazin-3-yl oligopyridines (BTP)
is found to separate AM from Ln with an excellent distribution ratio AM/Ln.
We study the solution structure of Ln-BTP and Ac-BTP complexes to determine
the causes of selectivity of BTP for Ac in liq-liq extraction experiences.
DETERMINATION OF STOECHIOMETRIE COMPLEX IN SOLUTION
The additions of BTP ligands produce a decrease of relaxivity
of Gd because BTP remove solvent molecules
from paramagnetic center and relax more slowly
in the bulk of the solution.
A plateau is observed for ligand/metal ratio of 3/1.
The highest stoechiometry of complex with BTP is Ln(R-BTP)3.
The NMR1H spectrums of BTP/Yb with ratio 1/1 to 3/1
are the same.
The BTP ligands form in solution tris-complex with Ln.
NMR spectrum of Yb(ClO4)3 with 1,2 and 3 equivament of CyMe4BTP
NMRD titration courbe of Gd(ClO4)3 by Me4BTP and CyMe4BTP
DETERMINATION OF STRUCTURE COMPLEX IN SOLUTION
Yb(CyMe4BTP)3:: CH ;4.2;1.3;-0.4 CH2 6.5; 5;4;2.3 Ar 0.9;-01
Paramagnetic shifts vs dipolar geometric factor of Yb(CyMe4BTP)3
The dipolar paramagnetic shift induced by Yb3+ are directly related to the geometry of complex and allow to deduce the solution structure of Ln(BTP)3.
The excellent correlation between experimental shifts and geometric factor G indicate that the solution and solid state structure are similar.
COSY spectrum of Yb(CyMe4BTP)3
COSY spectrum of Eu(Pr4BTP)3.
HSQC specrtum of Eu(Pr4BTP)3.
The conformation of Cy substituent is blocked. The Pr substituent of BTP become highly rigid when the complexe with Ln is formed.
CONCLUSION
The BTP ligands form high symmetric tris-complex with Ln and are extremely rigid. To our knowledge, is the first example of a rigidification
of substituent of ligand caused by the formation of a complex and induced an inequivalence brought about in methylene groups
that belong to substituents rather than to the core part of ligand. The futur NMR and NMRD studies of Am-BTP and Cm-BTP will help us
to explain causes of selectivity of BTP for Ac in liquid-liquid extraction experiences.
ACKNOWLEDGEMENTS
The authors wish to acknowledge the financial support of I.I.S.N (F.N.R.S.) and the ACSEPT Project (European Commission).