Misplaced Pages

Technetium(IV) oxide

Names
Other names Technetium dioxide
Identifiers
CAS Number	12036-16-7
3D model (JSmol)	Interactive image
ChEBI	CHEBI:26864
ChemSpider	5256775
Gmelin Reference	873611
PubChem CID	6857437
CompTox Dashboard (EPA)	DTXSID601316101
InChI InChI=1S/2O.Tc
SMILES O==O
Properties
Chemical formula	TcO2
Molar mass	130.00 g/mol
Appearance	Black solid
Density	6.9 g/cm
Melting point	1,100 °C (2,010 °F; 1,370 K) (sublimes)
Solubility in water	Insoluble
Solubility	Slightly soluble in acid (dihydrate)
Structure
Crystal structure	Isostructural to MoO2
Thermochemistry
Gibbs free energy (ΔfG)	−305.974±3.377 (dihydrate)
Related compounds
Other anions	Technetium(IV) chloride
Related compounds	Technetium(VII) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Infobox references

Technetium(IV) oxide, also known as technetium dioxide, is a chemical compound with the formula TcO₂ which forms the dihydrate, TcO₂·2H₂O, which is also known as technetium(IV) hydroxide. It is a radioactive black solid which slowly oxidizes in air.

Preparation

Technetium dioxide was first produced in 1949 by electrolyzing a solution of ammonium pertechnetate under ammonium hydroxide and this method is used for separating technetium from molybdenum and rhenium. There are now more efficient ways of producing the compound, such as the reduction of ammonium pertechnetate by zinc metal and hydrochloric acid, stannous chloride, hydrazine, hydroxylamine, ascorbic acid, by the hydrolysis of potassium hexachlorotechnate or by the decomposition of ammonium pertechnetate at 700 °C under an inert atmosphere:

2 NH₄TcO₄ → 2 TcO₂ + 4 H₂O + N₂

All of these methods except the last lead to the formation of the dihydrate. The most modern method of producing this compound is by the reaction of ammonium pertechnetate with sodium dithionite.

Properties

The dihydrate dehydrates to anhydrous technetium dioxide at 300 °C, and if further heated sublime at 1,100 °C under an inert atmosphere, however, if oxygen is present, it will react with the oxygen to produce technetium(VII) oxide at 450 °C. If water is present, pertechnetic acid is produced by the reaction of technetium(VII) oxide with water.

If technetium dioxide is treated with a base, such as sodium hydroxide, it forms the hydroxotechnetate(IV) ion, which is easily oxidized to pertechnetic acid in numerous ways, such as the reaction with alkaline hydrogen peroxide, concentrated nitric acid, bromine, or tetravalent cerium.

The solubility of technetium(IV) oxide is very low and is reported to be 3.9 μg/L. The main species when technetium dioxide is dissolved in water is TcO at pH below 1.5, TcO(OH) pH between 1.5 and 2.5, TcO(OH)₂ pH between 2.5 and 10.9, and TcO(OH)
₃ above pH 10.9. The solubility can be affected by adding various organic ligands such as humic acid and EDTA, or by the addition of hydrochloric acid. This can be a problem if technetium(IV) oxide is released into the soil, as it will increase the solubility.

If technetium dioxide is electrolyzed in acidic conditions, the following reaction occurs:

TcO₂·2H₂O → TcO
₄ + 4 H + 3 e

The electrode potential measured for this reaction is −837.2±10.0 kJ/mol.

The molar magnetic susceptibility of TcO₂·2H₂O was found to be χ_m = 244×10.

References

1. ^ A. G. Sharpe; H. J. Emeléus (1968). Advances in Inorganic Chemistry and Radiochemistry. Elsevier Science. p. 21. ISBN 9780080578606.
2. ^ J. A. Rard (1983). "Critical review of the chemistry and thermodynamics of technetium and some of its inorganic compounds and aqueous species". OSTI.GOV. U.S. Department of Energy Office of Scientific and Technical Information. doi:10.2172/5580852. OSTI 5580852. S2CID 98137163. Retrieved 4 November 2022.
3. ^ C. M. Nelson; G. E. Boyd; Wm. T. Smith Jr. (1954). "Magnetochemistry of Technetium and Rhenium". Journal of the American Chemical Society. 76 (2). ACS Publications: 348–352. doi:10.1021/ja01631a009.
4. ^ Edward Anders (1960). "THE RADIOCHEMISTRY OF TECHNETIUM". OSTI.GOV. U.S. Department of Energy Office of Scientific and Technical Information: 8. doi:10.2172/4073069. OSTI 4073069. Retrieved 4 November 2022.
5. L. B. Rogers (1949). "Electroseparation of Technetium from Rhenium and Molybdenum". Journal of the American Chemical Society. 71 (4): 1507–1508. doi:10.1021/ja01172a520.
6. ^ Bradley Covington Childs (2017). Volatile Technetium Oxides: Implications for Nuclear Waste Vitrification. UNLV Theses, Dissertations, Professional Papers, and Capstones (Thesis). doi:10.34917/10985836.
7. ^ Edward Andrews (1959). "Technetium and Astatine Chemistry". Annual Review of Nuclear Science. 9. Annual Reviews: 203–220. Bibcode:1959ARNPS...9..203A. doi:10.1146/annurev.ns.09.120159.001223.
8. Nancy J. Hess; Yuanxian Xia; Dhanpat Rai; Steven D. Conradson (2004). "Thermodynamic Model for the Solubility of TcO₂·xH₂O(am) in the Aqueous Tc(IV) – Na – Cl – H – OH – H₂O System". Journal of Solution Chemistry. 33 (2): 199–226. doi:10.1023/B:JOSL.0000030285.11512.1f. S2CID 96789279.
9. Baohua Gu; Wenming Dong; Liyuan Liang; Nathalie A. Wall (2011). "Dissolution of Technetium(IV) Oxide by Natural and Synthetic Organic Ligands under both Reducing and Oxidizing Conditions". Environmental Science & Technology. 45 (11): 4771–4777. Bibcode:2011EnST...45.4771G. doi:10.1021/es200110y. PMID 21539349.

• Technetium compounds
• Oxides