On the nature of heptavalent technetium in concentrated nitric and perchloric acid

The speciation of Tc(+7) was performed in HClO4 and HNO3 by 99-Tc NMR, UV–Vis and XAFS spectroscopy. The speciation of Tc(+7) depends on the concentration and strength of the acid. Pertechnetic acid, HTcO4, forms above 8 M HClO4 while in concentrated HNO3, [TcO4]− is still the predominant species. EXAFS spectroscopy shows that the structure of HTcO4 in HClO4 is similar to the one in H2SO4. The reactivity of Tc(+7) was analyzed in the frame of the partial charge model. The partial charge calculated on the Tc atoms (ΔTc) indicates that HTcO4 (ΔTc = +057) is more electrophilic than [TcO4]− (ΔTc = +0.52). The difference in the oxidizing properties between [TcO4]− and HTcO4 is given from the reaction of these species with 12 M HCl(aq). In 13 M sulfuric acid HTcO4 is reduced to Tc(+5) while [TcO4]− is not reduced in 6 M H2SO4.

The speciation of Tc(+7) was performed in HClO4 and HNO3 by 99-Tc NMR, UV–Vis and XAFS spectroscopy. In [1–8 M] HClO4 and [1–15.6 M] HNO3, Tc(+7) is present as [TcO4]−. Above 8 M HClO4, [TcO4]− is protonated and HTcO4 is formed.Figure optionsDownload as PowerPoint slideHighlights
► Speciation of Tc(+7) is performed in HClO4 and HNO3.
► In [1–8 M] HClO4 and [1–15.6 M] HNO3, Tc(+7) is present as [TcO4]−.
► For HClO4 > 8 M, Tc(+7) is present as HTcO4.
► In 13 M H2SO4, HTcO4 is reduced by 12 M HCl to Tc(+5).