Technetium is a transition metal for which there are only radioactive isotopes. Technetium-99 (Tc, t1/2: 2.1 x 105 years; βmax: 293.7 keV), the most abundant, exists in 9 oxidation states (-1 to +7). Its redox chemistry is highly interesting and facile. Understanding the relationship between Tc oxidation states and coordination environments that lead to stable complexes is important to address global problems. Tc is a major by-product of uranium fission and its separation from used nuclear fuel is a particular challenge. Likewise, separation of Tc from legacy waste from World War II and later defense activities is complicated because the Tc oxidation states and “ligands” present are largely unknown. Leakage of waste tanks results in release of the highly mobile pertechnetate ion, TcVIIO4- to the environment and remediation efforts are considering reduction to low valent Tc. Moreover, there are no suitable storage matrices for Tc largely due to the lack of knowledge of coordination environments necessary to stabilize appropriate Tc oxidation states. Polyoxometalates (POMs) are inorganic ligands that provide distinctive environments to stabilize Tc in unique oxidation states. POMs mimic “surface” binding sites and “defect” binding sites that are found in minerals, solid-state metal oxides and potential metal oxide wasteforms. Studies of Tc complexes of POMs as a function of Tc oxidation state report on Tc coordination, Tc redox chemistry, and Tc stability in these relevant matrices.

Fundamental chemistry of technetium-99 incorporated into polyoxometalates: Connecting metal oxide coordination sites with Tc oxidation state and speciation

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