Exploration of tetravalent molecular actinide halides
Creators: name: Gotthelf, Garret Israel
Publisher: name: No Publisher Supplied
Year: 2022

description: This thesis focuses on the synthesis and characterization of visually simple, but chemically complex molecular actinide halides. The central goal is to bind fluoride to actinide metals using safe and efficient methods and materials, where the metal fluoride bond can be accessible either in solution or its solid-state. The isolation of molecular uranium fluoride complexes is rare; therefore, novel simplistic methods for synthesizing uranium mono- and difluorides are needed. Using air and moisture-free conditions, uranium metal can be oxidized with elemental halide or copper(II) halides to create different organosoluble monomers. These monomers can be isolated in their solid-state as crystals and characterized by ultraviolet/visible (UV/vis) spectroscopy, infrared (IR) spectroscopy, nuclear magnetic resonance (NMR), and X-ray diffraction (XRD). Chapter two outlines the convenient synthesis and characterization of five unique uranium mono- and difluoride monomers. The monomers included (py)₄UF₂X₂ (X = Cl, Br, I), (DME)(py)₂UF₂I₂, (DME)₂UBr₃F, and the uranium salt [(MeCN)₉U][Cu₃I₆], are each studied for their unique crystallographic and spectroscopic properties.In chapter three, the reactivity of thorium was explored in the presence of elemental iodine and/or CuX₂ (X=F, Cl, Br). Thorium metal was oxidized in organic solvents using elemental halide or copper(II) halide oxidizing reagents to form four unique monomers and a dimer with bound fluoride ions. Reactions were accomplished in multiple solvents, dimethoxyethane (DME) and pyridine (py), and by introducing a bidentate ligand (2,2-bipyridine) as a neutrally charged coordinating ligand. Variations in stoichiometry and solvent environment resulted in the isolation of five new complexes (py)₄ThFX₃ (X= Br, I), (DME)₂ThBr₃F, [(bipy)₂(py)₂ThF₂I][I], and (py)₇Th₂F₂I₃(µ-F)₃. Diamagnetic thorium(IV) reactions were tracked using ¹⁹F-NMR resulting in the first known ¹⁹F resonance for molecular thorium fluorides. A thorough characterization of these thorium complexes and the analysis of their bonding and ¹⁹F-NMR chemical shifts are discussed.The effect of ancillary halides on thorium coordination chemistry was further expanded by exploring soft-donor chalcogenolate ligands. Thorium metal was oxidized in the presence of PhEEPh (E= S, Se), elemental iodine and catalytic mercury. Elemental chalcogen (either sulfur or selenium) was subsequently added to the thorium-chalcogenolate solutions. This reaction resulted in the oxidation of the (EPh)⁻¹ ligands to PhEEPh and the reduction of E to E²⁻, which bind to the electropositive Th(IV) metal centers. This reaction method was used to isolate four hexanuclear thorium compounds (py)₁₂Th₆I₆(E)₉ (E= S, Se), (py)₆(THF)₆Th₆I₆Se₉, and (THF)₁₂Th₆I₆S₉. These products were analyzed by NMR, Polycrystalline X-Ray Diffraction (PXRD), IR, and elemental analysis. The synthesis and characterization of these hexamers, as well as the isolation of a thorium byproduct, dimeric (MeCN)₄Th₂(SPh)₄(µ-SPh)₄, is discussed in chapter four.Chapter five consists of the general methods and synthesis of other complexes, both actinide and non-actinide, that were isolated during this thesis research. Many of the isolated structures were unintended byproducts that could be reproduced or were reproducible products that were difficult to characterize. Future research projects could use these structures to explore the formation of halide clusters, actinide oxide-chalcogen hybrid materials, and low-valence actinide salts. Chapter six describes the experimental synthesis of the 43 structures that were isolated by Low-Temperature X-Ray Diffraction LT-XRD and the experimental results for the 16 structures mentioned in chapters two-four.