Properties of Pertechnic Acid

Abstract

Dilute aqueous pertechnic acid has long been known as strong monoprotic acid that behaves as a simple pertechnetate ion in aqueous solution. As pertechnic acid concentrates by evaporation, it becomes yellow and then dark red, and dark-red crystalline material may ultimately be obtained. We show that as pertechnic acid concentrates, at least three compounds are formed: a yellow viscous liquid, a colorless (not red) crystalline solid, and a small amount of an intensely colored red–purple compound. The colorless crystalline compound melts at 118 °C and can be melted and recrystallized several times with little decomposition. The red–purple compound is apparently not stable at room temperature and quickly decomposes if it is isolated. UV–vis spectra show that Beer’s law does not hold as pertechnic acid concentrates by evaporation. We report densities, 99Tc nuclear magnetic resonance spectra, and ultraviolet–visible absorption spectra for highly pure aqueous pertechnic acid (accompanied by the other technetium compounds that form) ranging from 1 to 14 M in technetium concentration.

Intramolecular Re···O Nonvalent Interactions as a Stabilizer of the Polyoxorhenate(VII)

“…The process of changing the color of pertechnetic acid is described in the work. 25 After 20 days, a dark green viscous liquid formed at the bottom of the flask, from which yellow-green crystals formed. Due to the high sensitivity of the crystals to humidity, the flask with the precipitate was transferred to a drybox, which was filled with dried argon.…”

A 70‐Year‐Old Mystery in Technetium Chemistry Explained by the New Technetium Polyoxometalate [H7O3]4[Tc20O68] ⋅ 4H2O

“…For Group 7, concentration of permanganic acid (HMnO 4 ) led to the Mn(MnO 4 ) 6 2− species [10] . A similar reaction with pertechnetic acid (HTcO 4 ) gave a mixture of products: a yellow species and a “mysterious” red product [11] . Despite numerous experimental and theoretical efforts, the nature of the red species has been an ongoing controversy in technetium chemistry for many decades.…”

“…The conditions for the observation of red color from the concentration of HTcO 4 solutions have been described and primarily depend on the reaction time. The rapid concentration (evaporation of warm solution under an N 2 gas flow) leads to the formation of a yellow species and ultimately to a solid described as HTcO 4 ⋅H 2 O; the authors state that a “ component intensively red will appear if the evaporation is done slowly .” [11] …”

Ammonium Pertechnetate in Mixtures of Trifluoromethanesulfonic Acid and Trifluoromethanesulfonic Anhydride

“… [26] In contrast, concentrated HTcO 4 is dark‐yellow and forms a dark‐red solid upon further evaporation. [27] A hypothetic “HReO 4 ” does not exist and must be described as a hydrated rhenium oxide Re 2 O 7 (OH 2 ) 2 . [28] In addition, the chemistry of oxocations (“metalyl” ions) of oxidation states +7 or higher are limited to a few compounds, such as rare group 8 complexes of the perosmyl(VIII) trioxo dication OsO 3 2+ or the perosmyl(VIII) dioxo tetracation OsO 2 4+ .…”