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Technetium‐99 (half‐life of 2.1 × 105 yrs, βmax = 0.29 MeV) is a hazardous radiological contaminant, which, in its predominant form of pertechnetate (TcO4–), is highly mobile in the environment. Most strategies for the removal of pertechnetate from the environment involve uptake and/or absorption of pertechnetate using resins, clays, cationic metal‐organic frameworks and even thorium borate ceramic like materials. Alternative approaches have involved the reduction and subsequent sequestration of lower valent technetium species using iron, sulfides, or iron sulfides. Our lab has explored this strategy using the lacunary alpha‐2 Wells–Dawson polyoxometalate (α2‐[P2W17O61]10–) to both reduce and sequester lower valent technetium, and we have reported on the ligand features that stabilize the reduced species. In this work we investigate the potential of "plenary" Keggin POMs (XW12O40n–) (X = P, Si, Al, n = 3, 4, 5, respectively) to both reduce TcO4– and stabilize the reduced Tc species. Specifically, we report on the mechanism by which the reduction of technetium occurs and find that PW12, SiW12, and AlW12 promote the reduction of TcO4– to lower valent states. X‐ray absorption spectroscopy was used to confirm a combination of TcIV {in the form of TcO2·2H2O and Tc2(µ‐O)24+} and TcV, which is subsequently complexed into a POM defect as a TcV=O species. [ABSTRACT FROM AUTHOR]

Synthesis of technetium-99 (99Tc; t1/2: 2.1 × 105 years, βmax: 253 keV) materials is of importance in studies of the nuclear fuel cycle where Tc is a major fission product (6 % thermal yield from 235U and 239Pu), in understanding radioactive tank waste composition, and in identifying 99mTc compounds for nuclear medicine imaging. One of the most useful synthetic starting materials, (NBu4)TcOCl4, is susceptible to disproportionation in water to form TcO4- and TcIV species, especially TcO2 ·2H2O. This unwanted reaction is especially problematic when working with ligands bearing 'hard' donor atoms, such as oxygen, where the stability with the 'soft' TcV=O3+ core may be low. Polyoxometalates (POMs) are such ligands. They possess defect sites with four hard oxygen atoms and show low (ca. 108) stability constants with transition metals. Tc complexes of POMs are molecular-level models for Tc metal oxide solid-state materials and can provide information on coordination and redox environments of metal oxides that stabilize low-valent Tc. In order to synthesize pure Tc POM complexes [TcVO(α1-P2W17O61)]7- (TcVO- α 1) and [TcVO(α2-P2W17O61)]7- (TcVO- α 2) from (NBu4)TcOCl4, we have identified strategies that minimize formation of TcIV species and optimize the formation of pure TcV species. The parameters that we consider are the amount of ethylene glycol, which is employed as a 'transfer ligand' to prevent hydrolysis of (NBu4)TcOCl4, and the precipitating agent. The TcIV species that contaminates the non-optimized syntheses is likely a TcIV μ-oxido-bridged dimer [TcIV-(μ-O)2-TcIV]. We also employ a novel procedure where the α 2 ligand is photoactivated and reduced (in the presence of a sacrificial electron donor) to subsequently reduce TcVIIO4- to an isolatable TcVO- α 2 product that is remarkably free of TcIV. [ABSTRACT FROM AUTHOR]

B The Front Cover b shows the New York City skyline as a backdrop to the general reaction depicting the photoreduction of pertechnetate (TcO SB 4 sb SP - sp ) to low valent Tc. The skyline of New York City accentuates the excellent science conducted in New York City and CUNY's proud service to the diverse population of NYC. The skyline of New York City accentuates the excellent science conducted in New York City and CUNY's proud service to the diverse population of NYC. [Extracted from the article]