Pertechnetic acid

Pertechnetic acid (HTcO₄) is a compound of technetium that is produced by reacting technetium(VII) oxide (Tc₂O₇) with water or strong oxidizing acids, such as nitric acid, concentrated sulfuric acid, aqua regia. The dark red hygroscopic substance is a strong acid, with a pK_a of 0.32, as such it exists almost etirely as the pertechnetate ion in aqueous solution.

Use of strong enough acid solution, for example, concentrated sulfuric acid, can generate the protonated form, which then exists as the octahedral TcO₃(OH)(H₂O)₂ dihydrate complex.