ABSTRACT
The pursuit of a trivalent plutonium halide phosphine oxide compound, e.g., "PuBr3(OPR)3," instead led to the isolation of the tetravalent trans-PuIVBr4(OPCy3)2, PuBr/Cy, compound by spontaneous oxidation of PuIII. The donating nature of phosphine oxides has allowed the isolation and characterization of PuBr/Cy by crystallographic, multinuclear NMR, solid state, and solution phase UV-vis-NIR spectroscopic techniques. The presence of a putative plutonyl(VI) complex formulated as "trans-PuVIO2Br2(OPCy3)2" was also observed spectroscopically and tentatively by single-crystal X-ray diffraction as a cocrystal of PuBr/Cy. A series of trans-ThX4(OPCy3)2 (X = Cl, ThCl/Cy; Br, ThBr/Cy; I, ThI/Cy) complexes were synthesized for comparison to PuBr/Cy. The triphenylphosphine oxide, OPPh3, complexes, trans-AnI4(OPPh3)2 (An = Th, ThI/Ph; U, UI/Ph), were also synthesized for comparison, completing the series trans-UX4(OPPh3)2 (X = Cl, Br, I), UX/Ph. To enable the synthesis of ThI/Cy and ThI/Ph, a new nonaqueous thorium iodide starting material, ThI4(Et2O)2, was synthesized. The syntheses of organic solvent soluble ThI4L2 (L = Et2O, OPCy3, and OPPh3) are the first examples of crystallographically characterized neutral thorium tetraiodide materials beyond binary ThI4. To show the viability of ThI4(Et2O)2 as a starting material for organothorium chemistry, (C5Me4H)3ThI was synthesized and crystallographically characterized.
ABSTRACT
Perovskite ceramics have been extensively studied as host matrixes for radionuclide entrapment for nuclear waste disposal. As an expansion of these investigations, cerium, neodymium, and plutonium were incorporated into a perovskite phase, ACu3FeTi3O12 (A = Nd, Ce, Pu), using sol-gel methods under oxidizing and reducing atmospheres. The targeted materials contained varying levels of Ce3+ and Nd3+ on the A site, yielding potential compositions of Nd1- xCe xCu3FeTi3O12 ( x = 0, 0.1, 0.2, 0.3, 0.4, 0.8). However, interrogation of these materials shows that the maximum Ce3+ loading is achieved near x ≈ 0.2. A single composition with plutonium was targeted, Nd0.9Pu0.1Cu3FeTi3O12, in order to properly model more realistic loading levels for a repository-destined material. These compounds were characterized using powder X-ray diffraction with Rietveld refinements of the structures and by a variety of spectroscopic techniques. The data suggest that, in order to achieve Pu3+ substitution onto the A sites in the Nd0.9Pu0.1Cu3FeTi3O12, a reducing atmosphere must be employed. Otherwise, the redox activity of plutonium results in substitution onto multiple sites in the material as well as the formation of secondary phases such as TiO2.
