A 70‐year‐old mystery in technetium chemistry explained by the new technetium polyoxometalate [H7O3]4[Tc20O68]∙4H2Oстатья
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Аннотация:[H7O3]4[Tc20O68]∙4H2O [1] was prepared from an aqueous Tc2O7 solution concentrated over anhydrous H2SO4. [Tc20O68]4- is the first polyanionic species to be reported for Tc. The unit cell contains one centrosymmetric [Tc20O68]4- polyanion as well as hydronium ions and water molecules. The core of the structure consists of fourTc(V)O6 octahedra that form a square Tc4O4 ring. The four Tc(V)O6 octahedra are decorated by sixteen Tc(VII)O4 tetrahedra.Calculations show the bonding within the Tc4O4 ring to consist of a 3-center bond formed between each neighbouring pair of Tc atoms and their bridging oxygen. Calculations also indicate that a strong d → d electronic transition at 513 nm is the origin of the red colour of [1]. The characterization of red HTcO4 solutions by X-ray absorption spectroscopy has complemented the description of this compound in aqueous solution. The formation mechanisms in solution, includingthe possible role of technetium’s radioactivity in the formation of [1], are discussed.