Hydride and Oxides
The reaction of technetium with hydrogen produces the negatively charged hydride TcH2−
9 ion, which has the same type of crystal structure as (is isostructural with) ReH2−
9. It consists of a trigonal prism with a technetium atom in the center and six hydrogen atoms at the corners. Three more hydrogen atoms make a triangle lying parallel to the base and crossing the prism in its center. Although those hydrogen atoms are not equivalent geometrically, their electronic structure is almost the same. This complex has a coordination number of 9 (meaning that the technetium atom has nine neighbors), which is the highest for a technetium complex. Two hydrogen atoms in the complex can be replaced by sodium (Na+) or potassium (K+) ions.
Metallic technetium slowly tarnishes in moist air, and in powder form, will burn in oxygen. Two oxides have been observed: TcO2 and Tc2O7. Under oxidizing conditions, which tend to strip electrons from atoms, technetium(VII) will exist as the pertechnetate ion, TcO−
4.
At temperatures of 400–450 °C, technetium oxidizes to form the pale-yellow heptoxide:
- 4 Tc + 7 O2 → 2 Tc2O7
This compound adopts a centrosymmetric structure with two types of Tc-O bonds; their bond lengths are 167 and 184 pm, and the O-Tc-O angle is 180°.
Technetium heptoxide is the precursor to sodium pertechnetate:
- Tc2O7 + 2 NaOH → 2 NaTcO4 + H2O
Black-colored technetium dioxide (TcO2) can be produced by reduction of heptoxide with technetium or hydrogen.
Pertechnetic acid (HTcO4) is produced by reacting Tc2O7 with water or oxidizing acids, such as nitric acid, concentrated sulfuric acid, aqua regia, or a mixture of nitric and hydrochloric acids. The resulting dark red, hygroscopic (water absorbing) substance is a strong acid and easily donates protons. In concentrated sulfuric acid Tc(VII) tetraoxidotechnetate anion converts to the octahedral form of technetic(VII) acid TcO3(OH)(H2O)2.
The pertechnate (tetroxidotechnetate) anion TcO−
4 consists of a tetrahedron with oxygens in the corners and a technetium atom in the center. Unlike permanganate (MnO−
4), it is only a weak oxidizing agent. Pertechnate is often used as a convenient water-soluble source of technetium isotopes, such as 99mTc, and as a catalyst.
Read more about this topic: Technetium Compounds, Characteristics, Chemical Properties