Technetium hexafluoride
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| Identifiers | |
|---|---|
13842-93-8  |
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| Properties | |
| TcF6 | |
| Molar mass | 212 g/mol (98Tc) |
| Appearance | golden-yellow crystals[1] |
| Density | 3,58 g/cm3 (−140 °C), solid[2] |
| Melting point | 37.4 °C (99.3 °F; 310.5 K)[1] |
| Boiling point | 55.3 °C (131.5 °F; 328.4 K)[1] |
| Structure | |
| cubic | |
| Vapor pressure | {{{value}}} |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |
Technetium hexafluoride or technetium(VI) fluoride (TcF6) is a yellow inorganic compound with a low melting point. It was first identified in 1961.[3] In this compound, technetium has an oxidation state of +6, the highest oxidation state found in the technetium halides. The other such compound is technetium(VI) chloride, TcCl6. In this respect, technetium differs from rhenium, which forms a heptafluoride, ReF7.[4] Technetium hexafluoride occurs as an impurity in uranium hexafluoride, as technetium is a fission product of uranium.
Preparation
Technetium hexafluoride is prepared by heating technetium metal with an excess of F2 at 400 °C.[3]
- Tc + 3 F
2 → TcF
6
Description
Technetium hexafluoride is a golden-yellow solid at room temperature. Its melting point is 37.4 °C and its boiling point is 55.3 °C.[1]
Technetium hexafluoride undergoes a solid phase transition at −4.54 °C. Above this temperature (measured at 10 °C), the solid structure is cubic. Lattice parameters are a = 6.16 Å. There are two formula units (in this case, discrete molecules) per unit cell, giving a density of 3.02 g·cm−3. Below this temperature (measured at −19 °C), the solid structure is orthorhombic space group Pnma. Lattice parameters are a = 9.55 Å, b = 8.74 Å, and c = 5.02 Å. There are four formula units (in this case, discrete molecules) per unit cell, giving a density of 3.38 g·cm−3. At −140 °C, the solid structure is still orthothombic, but the lattice parameters are now a = 9.360 Å, b = 8.517 Å, and c = 4.934 Å, giving a density of 3.58 g·cm−3.[2]
The TcF6 molecule itself (the form important for the liquid or gas phase) has octahedral molecular geometry, which has point group (Oh). The Tc–F bond length is 1.812 Å.[2] Its magnetic moment has been measured to be 0.45 μB.[5]
Properties
Physical
TcF6 is octahedral, as shown by infrared and Raman spectra.[6][7] Its low-temperature orthorhombic form converts to the higher symmetry body-centred cubic form at room temperature, like other metal hexafluorides such as RhF6 and OsF6.[8] Preliminary measurements of magnetic moment yield a value of 0.45 µB, which is lower than expected for a d1 octahedral compound.[9]
Chemical
TcF6 reacts with alkaline chlorides in iodine pentafluoride (IF5) solution to form hexafluorotechnetates.[10][11] TcF6 disproportionates on hydrolysis with aqueous NaOH to form a black precipitate of TcO2.[3] In hydrogen fluoride solution, TcF6 reacts with hydrazinium fluoride to yield N2H6TcF6 or N2H6(TcF6)2.[12]
References
- ↑ 1.0 1.1 1.2 1.3 CRC Handbook of Chemistry and Physics, 90th Edition, CRC Press, Boca Raton, Florida, 2009, ISBN 978-1-4200-9084-0, Section 4, Physical Constants of Inorganic Compounds, p. 4-93.
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- ↑ Henry Selig, Fred A. Cafasso, Dieter M. Gruen, John G. Malm: "Magnetic Susceptibility of ReF6", in: Journal of Chemical Physics, 1962, 36 (12), S. 3440–3444; doi:10.1063/1.1732477.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
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