Insights on the Formation of Uranium Bearing Clusters through the Reactivity of Uranyl Triperoxide Species, Synthesis of Uranium-Molybdenum Clusters, and Cluster Formation in Ionic Liquids

It was found that, for uranyl triperoxides (UTs) in solution, gamma radiation promoted the decomposition of terminally bonded peroxides leading to the formation of larger uranyl peroxide species. A solution comprised of only the uranyl peroxide cage cluster U₂₄ then began to degrade and precipitate out a uranyl oxyhydroxide hydrate phase. In the solid-state, after receiving a dose of 2 MGy of gamma radiation, one of the terminally bound peroxides of CaUT reacted with a nearby water to form two hydroxide ligands forming a calcium uranyl diperoxide dihydroxide species. LiUT saw loss of all peroxide upon higher doses of alpha radiation and a subsequent formation of a similar uranyl oxyhydroxide hydrate phase as the solution studies.

LiUT is the least reactive with CO₂ and simply forms layered sheets of uranyl polyhedra connected by oxide and hydroxide ligands. The sodium and potassium salts react with CO₂ to form a variety of mixed carbonate/peroxide species. The speciation of these mixed species is studied under aqueous conditions to reveal the importance of carbonate in the formation of larger uranyl peroxide species.

Ionic liquids were used as bifunctional reagents to provide a ligand source and solvent during syntheses. It was shown that the anion of the ionic liquid could bond to the dissolved uranyl ion to form new uranyl cluster compounds. This technique was then used to make a uranyl succinate framework structure.

Uranium was found to direct the formation of a new type of molybdenum blue polyoxometalate cluster, Mo₇₂U₈. Additionally, it was found that U(IV) could be used as both heterometal and molybdenum reductant in the formation of molybdenum blue wheel clusters. Through a dehydration induced phase change these wheels clusters condensed into sheets that connect through uranyl oxygen atom to molybdenum bridges. This type of bond is unprecedented and marks a new method of study for the so-called cation-cation interactions of the uranyl ion.

Finally, the role of barium and lead in the formation of uranyl phosphonocarboxylates was studied. Two framework structures were found to crystallize due to the use of these counter cations that were unlike any other reported structures.