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| Identifiers | |
|---|---|
3D model (JSmol) | |
| ChemSpider | |
| |
| |
| 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 | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Technetium hexafluoride ortechnetium(VI) fluoride (TcF6) is a yellowinorganic compound with a lowmelting point. It was first identified in 1961.[3] In this compound, technetium has anoxidation state of +6, the highest oxidation state found in the technetiumhalides. In this respect, technetium differs from rhenium, which forms a heptafluoride,ReF7.[4] Technetium hexafluoride occurs as an impurity inuranium hexafluoride, as technetium is afission product ofuranium (spontaneous fission innatural uranium, possible contamination frominduced fission inside the reactor inreprocessed uranium). The fact that the boiling point of the hexafluorides of uranium and technetium are very close to each other presents a problem in usingfluoride volatility innuclear reprocessing.
Technetium hexafluoride is prepared by heating technetium metal with an excess of F2 at 400 °C.[3]
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 solidphase transition at −4.54 °C. Above this temperature (measured at 10 °C), the solid structure iscubic.Lattice parameters area = 6.16 Å. There are twoformula units (in this case, discrete molecules) perunit cell, giving a density of 3.02 g·cm−3. Below this temperature (measured at −19 °C), the solid structure isorthorhombic space groupPnma.Lattice parameters area = 9.55 Å,b = 8.74 Å, andc = 5.02 Å. There are fourformula units (in this case, discrete molecules) perunit cell, giving a density of 3.38 g·cm−3. At −140 °C, the solid structure is still orthothombic, but the lattice parameters are nowa = 9.360 Å,b = 8.517 Å, andc = 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) hasoctahedral molecular geometry, which has point group (Oh). The Tc–Fbond length is 1.812 Å.[2] Itsmagnetic moment has been measured to be 0.45μB.[5]
TcF6 isoctahedral, as shown byinfrared andRaman spectra.[6][7] Its low-temperatureorthorhombic form converts to the higher symmetrybody-centred cubic form at room temperature, like other metal hexafluorides such as RhF6 and OsF6.[8] Preliminary measurements ofmagnetic moment yield a value of 0.45μB, which is lower than expected for a d1 octahedral compound.[9]
TcF6 reacts with alkalinechlorides iniodine pentafluoride (IF5) solution to form hexafluorotechnetates.[10][11] TcF6 disproportionates onhydrolysis with aqueousNaOH to form a black precipitate ofTcO2.[3] Inhydrogen fluoride solution, TcF6 reacts withhydrazinium fluoride to yield N2H6TcF6 or N2H6(TcF6)2.[12]
