Applying Supramolecular Chemistry to the Synthesis and Characterization of Uranium Bearing Hybrid Materials
Open AccessThis dissertation focuses on the synthesis and characterization of uranium-containing metal-organic hybrid materials. These materials self-assemble under aqueous conditions aided by supramolecular interactions which help define the solid state structures. This work set out to create families of uranium-bearing hybrid materials which may be utilized in discerning the limits of supramolecular inorganic-organic chemistry as a means of crystal engineering. As the many forces which achieve the organization of molecules and ions in the solid state (including hydrogen bonds, π-π and halogen-halogen interactions, and weaker interactions) are not all apparent when attempting syntheses of new materials, known supramolecular synthons are a convenient way of summarizing major interactions. As these synthons are explored in the synthesis of metal-organic hybrid materials, researchers may begin to move away from chance results and towards creating desired structure types. Until our efforts, supramolecular chemistry has been significantly underdeveloped in actinide systems.We first demonstrate the utility of applying supramolecular chemistry to uranium in a system where the [UO2X4]2- anion interacts predictably with linear bipryidinium cations to form a previously observed transition metal synthon (M-Cl2···H-N). The resulting bifurcated "ribbon motif" was realized in many such phases, absent only when the organic tecton diverged from the linear prototypes seen in other work.viiWhile the above uranium-bearing tectons are diverse and may provide a route to many new phases and families of materials, they too have their limitations; namely they semi-regularly produce a `ribbon' motif within the solid state and limit our predictive efforts to 1-D.We next show that limited metal-ligand coordination yields a second method for creating new uranium-bearing tectons, which have the added benefit of utilizing additional supramolecular synthons, such as halogen-halogen interactions. This second approach exploits our knowledge of hard-soft acid base (HSAB) theory to choose a ligand, 4-halobenzoic acid, that coordinates to uranium on one side, while presenting a supramolecular entity outward. This coordination creates a tecton that presents a `face' capable of halogen-halogen interactions with sister tectons in the solid state.Both methods represent a significant step in utilizing crystal engineering to create families of uranyl-bearing hybrid materials.
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