The hydrothermal synthesis, characterization, and properties of novel actinide materials containing heavy oxoanions

A series of novel uranium- and neptunium-based materials containing the heavy oxoanions selenite and tellurite are presented. These compounds were synthesized using hydrothermal methods that have consistently shown to provide access to otherwise unattainable compounds that display rich structural chemistry as well as interesting physiochemical properties. Many of the uranium-containing compounds presented herein are related to a handful of rare uranyl minerals. These supergene minerals were believed to form from primary mineral phases generated by hydrothermal environments in nature. Therefore it is of interest to understand the systematics of these compounds by comparing and contrasting newly synthesized compounds with other synthetic phases, as well as with their family of minerals, in order to identify similar uranyl oxoanion topologies and bonding motifs. Also, understanding the complexation of 238U and 237Np by 79SeO32- will help to decipher which species may eventually form from nuclear fuel cycle wastes, and how this complex formation may govern the mobility of these radionuclides over time. Finally, these compounds can display interesting physiochemical properties such as second harmonic generation (SHG), fluorescence, magnetism, ion exchange, and catalysis. The structures presented in this dissertation were elucidated via single crystal X-ray diffraction and were further characterized by a variety of techniques including: IR and UV-Vis spectroscopy, elemental analysis, and Electron Dispersive Analysis by X-rays (EDAX).; This dissertational work presents the hydrothermal synthesis and crystal structures of 22 novel Uranium (VI) and Neptunium (V) selenites and tellurites. A variety of novel structural topologies have been observed in these new compounds, as well as some that mimic naturally occurring minerals. These reactions have led to the formation of the parsonite and phosphuranylite sheet topologies. Furthermore, the unusual Te2O64- anion has been observed and explained through computational experiments. Finally, neptunyl selenites have been synthesized that contain cation-cation interactions (CCIs) and the magnetic properties of these compounds have been investigated.