Molecular Precursors to Actinide Oxide and Nitride Nanomaterials By Mark D. Straub A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemistry in the Graduate Division of the University of California, Berkeley Committee in charge: Professor John Arnold, Chair Professor Kenneth Raymond Professor Karl van Bibber Spring 2021 Molecular Precursors to Actinide Oxide and Nitride Nanomaterials All rights reserved. Copyright of this Dissertation is held by Mark D. Straub. This work is protected against unauthorized copying under Title 17, United States Code. Chapter 2 was adapted with permission from Mark D. Straub, John Arnold, Julianna Fessenden, and Jaqueline Kiplinger. “Recent Advances in Nuclear Forensic Chemistry.” Anal. Chem., 2021, 93, 3-22. Copyright 2021 American Chemical Society. Chapter 3 was adapted with permission from Mark D. Straub, Jennifer Leduc, Michael Frank, Aida Raauf, Trevor D. Lohrey, Stefan G. Minasian, Sanjay Mathur, and John Arnold. “Chemical Vapor Deposition of Phase‐Pure Uranium Dioxide Thin Films from Uranium(IV) Amidate Precursors.” Angew. Chem., 2019, 58, 5749-5753. Copyright 2019 Wiley-VCH. Chapter 4 was adapted with permission from Mark D. Straub, Erik T. Ouellette, Michael A. Boreen, Jacob A. Branson, Alex Ditter, A. L. David Kilcoyne, Trevor D. Lohrey, Matthew A. Marcus, Maria Paley, José Ramirez, David K. Shuh, Stefan G. Minasian, and John Arnold. “Thorium Amidates Function as Single-Source Molecular Precursors for Thorium Dioxide.” Chem. Commun., 2021, in press, with permission from the Royal Society of Chemistry. Chapter 5 was adapted with permission from Mark D. Straub, Stephan Hohloch, Stefan G. Minasian, and John Arnold. “Homoleptic U(III) and U(IV) Amidate Complexes.” Dalton Trans., 2018, 47, 1772-1776, with permission from the Royal Society of Chemistry. Chapter 6 was adapted with permission from Mark D. Straub, Liane M. Moreau, Yusen Qiao, Erik T. Ouellette, Michael A. Boreen, Trevor D. Lohrey, Nicholas S. Settineri, Stephan Hohloch, Corwin H. Booth, Stefan G. Minasian, and John Arnold. “Amidinate Supporting Ligands Influence Molecularity in Formation of Uranium Nitrides.” Inorg. Chem., 2021, in press. Copyright 2021 American Chemical Society. Abstract Molecular Precursors to Actinide Oxide and Nitride Nanomaterials By Mark D. Straub Doctor of Philosophy in Chemistry University of California, Berkeley Professor John Arnold, Chair 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 1 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. 2 Molecular Precursors to Actinide Oxide and Nitride Nanomaterials Table of Contents Acknowledgements ......................................................................................................................iv Chapter 1. Motivations for the Study of Actinide Molecules and Materials ................................ 1 Actinide Nanomaterials as Model Systems for Nuclear Fuels ....................................................... 2 Selection of Precursors for Actinide Oxide and Nitride Nanomaterials ......................................... 4 Linking the Molecular and Materials Chemistry of the Actinides ................................................. 6 References ..................................................................................................................................... ..7 Chapter 2. Recent Advances in Nuclear Forensic Chemistry.....................................................10 Introduction ................................................................................................................................... 11 Nuclear Forensics: Objectives and Scope ..................................................................................... 11 Overview of Analytical Methods .................................................................................................. 12 Electromagnetic Spectroscopy and Diffraction ............................................................................ 15 Radiochemical Techniques ........................................................................................................... 20 Mass Spectrometry........................................................................................................................ 22 Microanalytical Techniques .......................................................................................................... 24 Interface with Synthetic Chemistry .............................................................................................. 30 Post-detonation Analysis .............................................................................................................. 34 Conclusions ................................................................................................................................... 39 References ..................................................................................................................................... 40 Chapter 3. Chemical Vapor Deposition of Phase-Pure Uranium Dioxide Thin Films from Uranium(IV) Amidate Precursors ........................................................................................ 49 Introduction ................................................................................................................................... 50 Results and Discussion ................................................................................................................. 51 Summary and Conclusions ........................................................................................................... 58 Experimental ................................................................................................................................. 58 i References ..................................................................................................................................... 66 Chapter 4. Thorium Amidates Function as Single-Source Molecular Precursors for Thorium Dioxide .......................................................................................................................................... 68 Introduction ................................................................................................................................... 69 Results and Discussion ................................................................................................................. 69 Summary and Conclusions ........................................................................................................... 73 Experimental ................................................................................................................................. 74 References ....................................................................................................................................
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