Synthesis and Characterization of Actinide-Bearing Compounds Using Ionic Liquid Media

The goal of this dissertation is to explore the fundamental chemistry of various hexavalent uranium and neptunium compounds with a focus on crystal structure determination to better understand the formation and stabilization of actinide compounds in the solid-state. Solvothermal synthetic approaches using both aqueous and ionic liquid solvents were implemented to grow crystals yielding a variety of different organic-inorganic hybrid structures. Special emphasis is placed on the use of ionic liquids as the main reaction medium, given the relatively few reports of their use in the synthesis of actinide-bearing compounds.

Projects were developed to further study organically stabilized uranyl sulfate materials, which are known for their rich structural diversity. The goal of the first of these is systematically changing solvothermal synthetic parameters to better understand how the chemical and heat treatment variables influence the resultant crystal structures. The second study investigates the way in which the organic cations and interstitial species coordinate to and stabilize uranyl sulfate structural units.

Projects were also developed to investigate uranyl phosphate chemistry, which has importance to separations and environmental remediation strategies. The first produced four novel uranyl phosphate crystal structures with unique topologies influenced by the incorporation of the diethyl phosphate anion from the ionic liquid. The role the organic on the organophosphate anion is further investigated by replacing the diethyl phosphate with dimethyl and dibutyl phosphate to see how the chemical system and the resulting crystal structures change.

The third set of projects explores more complex chemical systems, namely the addition of vanadium into the uranyl phosphate system and neptunium with ionic liquids. The addition of vanadium precursors promotes the crystallization of novel uranyl vanadate clusters with unusual shell architectures that are described and the solution speciation was analyzed. In the final study, isostructural uranyl and neptunyl compounds are synthesized to compare spectroscopic details to understand differences between the uranyl and neptunyl ions. Overall, these studies highlight the use of ionic liquids in the synthesis of novel uranyl and neptunyl compounds.