_oxide.png) | |
| Names | |
|---|---|
Other names
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| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider | |
| 873611 | |
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| Properties | |
| TcO2 | |
| Molar mass | 130.00 g/mol |
| Appearance | Black solid |
| Density | 6.9 g/cm3[1] |
| Melting point | 1,100 °C (2,010 °F; 1,370 K)[3] (sublimes) |
| Insoluble | |
| Solubility | Slightly soluble in acid (dihydrate)[2] |
| Structure | |
| Isostructural toMoO2[1] | |
| Thermochemistry | |
Gibbs free energy(ΔfG⦵) | −305.974±3.377[clarification needed units] (dihydrate) |
| Related compounds | |
Otheranions | Technetium(IV) chloride |
Related compounds | Technetium(VII) oxide |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Technetium(IV) oxide, also known astechnetium dioxide, is a chemical compound with the formula TcO2 which forms the dihydrate, TcO2·2H2O, which is also known astechnetium(IV) hydroxide. It is a radioactive black solid which slowly oxidizes in air.[1][4]
Technetium dioxide was first produced in 1949 by electrolyzing a solution ofammonium pertechnetate underammonium hydroxide and this method is used for separating technetium frommolybdenum andrhenium.[1][4][5] There are now more efficient ways of producing the compound, such as the reduction of ammonium pertechnetate byzinc metal andhydrochloric acid,stannous chloride,hydrazine,hydroxylamine,ascorbic acid,[4] by the hydrolysis ofpotassium hexachlorotechnate[3] or by the decomposition of ammonium pertechnetate at 700 °C under an inert atmosphere:[1][6][7]
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 withsodium dithionite.[8]
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 producetechnetium(VII) oxide at 450 °C.[1][3][7] If water is present,pertechnetic acid is produced by the reaction of technetium(VII) oxide with water.[6]
If technetium dioxide is treated with a base, such assodium hydroxide, it forms the hydroxotechnetate(IV) ion, which is easily oxidized topertechnetic acid in numerous ways, such as the reaction with alkalinehydrogen peroxide, concentratednitric acid,bromine, or tetravalentcerium.[1][7]
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 TcO2+ 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 ashumic acid andEDTA, or by the addition ofhydrochloric acid. This can be a problem if technetium(IV) oxide is released into the soil, as it will increase the solubility.[9]
If technetium dioxide is electrolyzed in acidic conditions, the following reaction occurs:
Theelectrode potential measured for this reaction is−837.2±10.0 kJ/mol.[2]
The molarmagnetic susceptibility of TcO2·2H2O was found to beχm =244×106[clarification needed units].[3]
