UC Berkeley

Chapter 1. The overarching hypothesis and goals of this work are stated. Actinide molecules and nanomaterials are introduced as model systems for nuclear fuels and nuclear forensics. Routes to develop new actinide molecules and materials from bespoke molecular precursors are described.

Chapter 2. The current state of nuclear forensic chemistry is reviewed, with discussion of pre- and post-detonation scenarios. Advances in synthetic chemistry and actinide nanomaterials are emphasized, and their relevance to modern nuclear forensic capabilities is highlighted. Numerous real-world case studies from nuclear smuggling and weapons fallout are analyzed and discussed.

Chapter 3. Volatile uranium(IV) amidate complexes are synthesized as single-source molecular precursors to uranium oxide films. These complexes are found to decompose to UO2 through an alkene elimination mechanism, enabling epitaxial stabilization of stoichiometric UO2 on {111} silicon substrates. Chemical vapor deposition (CVD) of these single-source precursors yields crystalline, phase-pure UO2 films with a fir tree-like microstructure and a high surface area.

Chapter 4. Thorium(IV) amidate complexes are synthesized as volatile single-source molecular precursors for thorium dioxide. The effects of different ligand substituents towards the thermal properties and decomposition mechanism of the precursors are explored. Using X-ray diffraction and spectroscopy to characterize the decomposition products, the purity and crystallinity of ThO2 samples formed from these precursors are compared.

Chapter 5. The syntheses of the first homoleptic uranium(III) and uranium(IV) amidate complexes are described. These can be interconverted by chemical reduction/oxidation, showing an unusual change in coordination number from four in the uranium(III) complex to eight in the uranium(IV) complex in the solid state structures.

Chapter 6. Three new bridging uranium nitride complexes are synthesized from amidinate-supported precursors and their structural and magnetic properties are explored. The amidinate ligand substituents are seen to affect the composition and nuclearity of the nitride products. Using 15N labeling and acid hydrolysis, the nitrido ligands in all three complexes are proven to form via two-electron reduction of azide. Uranium complexes in the +3, +4, and +5 oxidation states are synthesized and magnetically characterized to provide a reference for the magnetic behavior of the nitrides, all three of which are found to contain uranium(IV) at each metal center.

Appendix. Various projects that have not yet been published are discussed. These include uranium(IV) and uranium(VI) amidate precursors, uranium(IV) heterometallic complexes, actinide triazenide complexes, and precursors for thorium nitride materials.