Raman spectra of all the actinide(V) (except Pa) and actinide(VI) complexes in 2 M Na2C03 solutions have been obtained.A resonance Raman effect was observed for Np(VI), Pu(VI), and Am(VI) and found to be related to the position of the charge-transfer bands observed in the corresponding electronic spectra and to the formal potential of actinide(VI)/actinide(V) couples in carbonate solution. No resonance effect was observed in the Raman spectrum of U(VI). The symmetric stretching frequency (¡q) of the M022+ group was shifted in carbonate solutions as compared to acidic noncomplexing solutions and decreased regularly with an increase in the atomic number of the actinide considered. In contrast, the iq frequencies of the M02+ group for actinide(V) species in carbonate solutions did not vary as the atomic number of the actinide increased. In comparison to the iq frequencies in acidic solutions, in carbonate solution a small negative shift was observed for vx of Np(V) and a positive shift was obtained for vx of Am(V). The Raman spectra of Na3M02(C03)2 solid compounds were obtained for M = Np, Pu, and Am. The iq frequencies of the M02+ ions decreased linearly with increasing atomic number of the actinide and were higher than the corresponding values for aqueous M02+ ions. The differences in behavior observed between actinide(V) and -(VI) species in noncomplexing media and in carbonate media may be related to possible hydrogen bonding between the oxygen of the actinide(V) oxycation and water molecules.
The aim of this work is to understand the reasons for the selectivity shown in the complexation by unsaturated heteropolyanions (ΗΡΑ) of actinides (An) which are oxidized to the number +IV. Different studies have been carried out, both in solution and in solid state, on P 2 W 17 OM~ and its complexes with Zn 2+ , UOr, Ce 4+ , Th 4+ and U 4+ to characterize the nature of the complexation site offered to the cation. Among the actinides(IV), the U 4+ ion has been selected due to its singular spectroscopic and magnetic properties.An initial series of studies, in solution, using NMR 3 'P has thus enabled us to characterize these complexes and to compare them to those formed with the complexing agent PWnOf,. This body of data allows to identify an identical complexation site for both ligands. An analysis of the NMR 31 P spectrum of U(P 2 W 17 0 61 )J 6 " 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(P 2 W, 7 0 61 )r in solid state. Following synthesis, elementary and thermogravimetric analyses have confirmed the formula K 16 [U(P 2 W, 7 0 6 ,) 2 ] · 38 H 2 0 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 U 4+ of D id 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.
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