The coordination of actinide cations and pertechnetate anions using expanded porphyrins and other polypyrrolic ligands
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Using nuclear energy for the production of electricity is hindered by significant waste management risks. The production of plutonium from power reactors amounts to as much as 7000 metric tons worldwide. Most of this is dilute and contained in spent reactor fuel, making the optimization of process chemistry and waste management of radioactive materials an environmental issue of tremendous importance. Addressing this concern are efforts to achieve the separation or isolation of radioactive elements, including actinide cations and technetium anions. This encourages the exploration of f-element and radionuclide chemistry, and creates a need for novel systems that are capable of coordinating actinide cations or pertechnetate anions with high specificity. The porphyrins are recognized as being excellent cation complexation agents. While volumes of work have been produced concerning the coordination of transition metals with porphyrin, examples of actinide porphyrin complexes are limited. Research in the Sessler group has focused on the synthesis and characterization of expanded porphyrins and using them in various applications, in particular, lanthanide coordination and anion coordination. This led to the consideration that these ligands or modified analogues, might aid in developing systems for the complexation-based remediation of radioactive wastes, including neptunium, plutonium, and americium cations in various oxidation states, as well as pertechnetate anions. This dissertation describes the development of three distinct projects in this area: using expanded porphyrins to coordinate actinide cations (NpO2 + , PuO2 2+), using sapphyrin (a particular expanded porphyrin shown to coordinate phosphate anions) to coordinate pertechnetate anions (TcO4 - ), and using linear oligopyrroles, (precursors of these expanded porphyrin systems) as extracting agents for americium cations, (Am3+). This has produced the first crystal structure of an all-aza bound neptunium complex, as well as spectroscopic evidence for other expanded porphyrin neptunium and plutonium complexes. Pertechnetate binding by sapphyrin is demonstrated by changes in the ultraviolet and visible absorption spectrum of sapphyrin. Scintillation techniques were used to test the ability of various linear oligopyrroles to extract americium(III) cations into organic solvents. This multifaceted project explores anion binding, organic, and inorganic synthesis, and provides information of a fundamental nature that could be used to generate improved waste remediation processes.