The aim of this work is to understand the reasons for the selectivity shown in the complexation by unsaturated heteropolyanions (HPA) of actinides (An) which are oxidized to the number +IV. Different studies have been carried out, both in solution and in solid state, on P2W17O6110- and its complexes with Zn2+, UO22+, Ce4+, Th4+ and U4+ to characterize the nature of the complexation site offered to the cation. Among the actinides(IV), the U4+ ion has been selected due to its singular spectroscopic and magnetic properties.An initial series of studies, in solution, using (NMRP)-P-31 has thus enabled us to characterize these complexes and to compare them to those formed with the complexing agent PW11O398-. This body of data allows to identify an identical complexation site for both ligands. An analysis of the (NMRP)-P-31 spectrum of U(P2W17O61)(2)(16-) has shown a plane of symmetry passing through the actinide and enables us to confirm the hypothesis of a transfer of intermetallic charge on the U-O-W bonds, observed in the visible absorption spectrum of the complex.The second part of the work is the study of U(P2W17O61)(2)(16-) in solid state. Following synthesis, elementary and thermogravimetric analyses have confirmed the formula K-16[U(P2W17O61)(2)]. 38 H2O of the compound. This solid, characterized by spectrophotometry of visible and IR absorption, shows absorption bands of energy identical to those of the coordination compound in solution. We then measured magnetic susceptibility as a function of temperature, characteristic of the Curie-Weiss law. The Curie constant is characteristic of a site occupied by the cation U4+ of D-4d symmetry ("Archimedes" antiprism). This eight coordinate form derived from the cube is entirely favourable to the stability of the actinide(IV) and, associated with a high charge density, tends towards selective complexation of these ions.

P-31 NMR is useful for the study of the hydrolytic and radiolytic degradation of tributylphosphate (TBP), extractant used for nuclear fuel reprocessing. Each degradation product can be easily identified and measured. NMR can also be used to study the behaviour of technetium, (Tc-99), a fission product which able to cause problems in the implementation of the process. N,N-dialkylamides are alternative extractants to TBP for fuel reprocessing. Their extracting properties can also be studied using NMR. An NMR conformational analysis helps us to understand the behaviour of these new molecules.