Technetium is a radioactive metal in group 7 of the periodic table. KMnO₄, a heptavalent oxo-salt of technetium’s lighter analogue manganese, is well known as an oxidant. As a rare and radioactive element, technetium is not a common staple of most laboratories. However, like manganese, it is able to form heptavalent oxo-compounds, for example, the KMnO₄ analogue KTcO₄ and the corresponding acid HTcO₄.

John McCloy, Pacific Northwest Laboratory, Richland, and Washington State University, Pullman, both WA, USA, and colleagues have investigated the behavior of aqueous technic acid (HTcO₄) solutions upon evaporation of water. A pure pertechnic acid solution was prepared from KTcO₄ by a sequence of recrystallization and cation-exchange processes. The technetium content of the resulting solutions was determined by liquid scintillation counting (LSC), making use of technetium’s radioactivity.

The team observed a color change from colorless to yellow to red during the evaporation of water. The concentrated solutions and isolated compounds were analyzed  by ⁹⁹Tc NMR and UV-Vis spectroscopy, density determination, and thermal analysis. Three different compounds were identified. A colorless solid assumed to be the monohydrate of pertechnic acid, a yellow liquid, probably H₅TcO₆, and a dark red solid considered to be Tc₂O₅, which underwent quick disproportionation.

The researchers could show that only a negligible loss of technetium occurred during the evaporation process. They plan to perform X-ray diffraction experiments for the conclusive determination of the structure and composition of the products.

• Properties of Pertechnic Acid,
  Chuck Soderquist, Jamie Weaver, Herman Cho, Bruce McNamara, Sergey Sinkov, John McCloy,
  Inorg. Chem. 2019.
  https://doi.org/10.1021/acs.inorgchem.9b01999