Technetium hexafluoride

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Technetium(VI) fluoride
Technetium-hexafluoride-2D.png
Identifiers
3D model (JSmol)
ChemSpider
PubChem CID
  • InChI=1S/6FH.Tc/h6*1H;/q;;;;;;+6/p-6
    Key: PRVOBRCYHYXCMU-UHFFFAOYSA-H
  • F[Tc](F)(F)(F)(F)F
Properties
TcF6
Molar mass 212 g/mol (98Tc)
Appearancegolden-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 their standard state (at 25 °C [77 °F], 100 kPa).
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Technetium hexafluoride or technetium(VI) fluoride (Tc F6) 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. 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 (spontaneous fission in natural uranium, possible contamination from induced fission inside the reactor in reprocessed uranium). The fact that the boiling point of the hexafluorides of uranium and technetium are very close to each other presents a problem in using fluoride volatility in nuclear reprocessing.

Contents

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]

Related Research Articles

<span class="mw-page-title-main">Uranium hexafluoride</span> Chemical compound

Uranium hexafluoride (UF
6), (sometimes called "hex") is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile white solid that reacts with water, releasing corrosive hydrofluoric acid. The compound reacts mildly with aluminium, forming a thin surface layer of AlF3 that resists any further reaction from the compound. UF6 is used in the process of enriching uranium, which produces fuel for nuclear reactors and nuclear weapons.

Xenon tetroxide is a chemical compound of xenon and oxygen with molecular formula XeO4, remarkable for being a relatively stable compound of a noble gas. It is a yellow crystalline solid that is stable below −35.9 °C; above that temperature it is very prone to exploding and decomposing into elemental xenon and oxygen (O2).

<span class="mw-page-title-main">Xenon hexafluoride</span> Chemical compound

Xenon hexafluoride is a noble gas compound with the formula XeF6. It is one of the three binary fluorides of xenon, the other two being XeF2 and XeF4. All known are exergonic and stable at normal temperatures. XeF6 is the strongest fluorinating agent of the series. It is a colorless solid that readily sublimes into intensely yellow vapors.

Fluoride volatility is the tendency of highly fluorinated molecules to vaporize at comparatively low temperatures. Heptafluorides, hexafluorides and pentafluorides have much lower boiling points than the lower-valence fluorides. Most difluorides and trifluorides have high boiling points, while most tetrafluorides and monofluorides fall in between. The term "fluoride volatility" is jargon used particularly in the context of separation of radionuclides.

<span class="mw-page-title-main">Uranium tetrafluoride</span> Chemical compound

Uranium tetrafluoride is the inorganic compound with the formula UF4. It is a green solid with an insignificant vapor pressure and low solubility in water. Uranium in its tetravalent (uranous) state is important in various technological processes. In the uranium refining industry it is known as green salt.

<span class="mw-page-title-main">Uranium pentafluoride</span> Chemical compound

Uranium pentafluoride is the inorganic compound with the chemical formula UF5. It is a pale yellow paramagnetic solid. The compound has attracted interest because it is related to uranium hexafluoride, which is widely used to produce uranium fuel. It crystallizes in two polymorphs, called α- and β-UF5.

Osmium compounds are compounds containing the element osmium (Os). Osmium forms compounds with oxidation states ranging from −2 to +8. The most common oxidation states are +2, +3, +4, and +8. The +8 oxidation state is notable for being the highest attained by any chemical element aside from iridium's +9 and is encountered only in xenon, ruthenium, hassium, iridium, and plutonium. The oxidation states −1 and −2 represented by the two reactive compounds Na
2[Os
4(CO)
13] and Na
2[Os(CO)
4] are used in the synthesis of osmium cluster compounds.

<span class="mw-page-title-main">Plutonium hexafluoride</span> Chemical compound

Plutonium hexafluoride is the highest fluoride of plutonium, and is of interest for laser enrichment of plutonium, in particular for the production of pure plutonium-239 from irradiated uranium. This pure plutonium is needed to avoid premature ignition of low-mass nuclear weapon designs by neutrons produced by spontaneous fission of plutonium-240.

<span class="mw-page-title-main">Rhenium heptafluoride</span> Chemical compound

Rhenium heptafluoride is the compound with the formula ReF7. It is a yellow low melting solid and is the only thermally stable metal heptafluoride. It has a distorted pentagonal bipyramidal structure similar to IF7, which was confirmed by neutron diffraction at 1.5 K. The structure is non-rigid, as evidenced by electron diffraction studies.

A hexafluoride is a chemical compound with the general formula QXnF6, QXnF6m−, or QXnF6m+. Many molecules fit this formula. An important hexafluoride is hexafluorosilicic acid (H2SiF6), which is a byproduct of the mining of phosphate rock. In the nuclear industry, uranium hexafluoride (UF6) is an important intermediate in the purification of this element.

<span class="mw-page-title-main">Iridium hexafluoride</span> Chemical compound

Iridium hexafluoride, also iridium(VI) fluoride, (IrF6) is a compound of iridium and fluorine and one of the seventeen known binary hexafluorides. It is one of only a few compounds with iridium in the oxidation state +6.

<span class="mw-page-title-main">Molybdenum hexafluoride</span> Chemical compound

Molybdenum hexafluoride, also molybdenum(VI) fluoride, is the inorganic compound with the formula MoF6. It is the highest fluoride of molybdenum. A colourless solid, it melts just below room temperature and boils in 34 °C. It is one of the seventeen known binary hexafluorides.

<span class="mw-page-title-main">Chromyl fluoride</span> Chemical compound

Chromyl fluoride is an inorganic compound with the formula CrO2F2. It is a violet-red colored crystalline solid that melts to an orange-red liquid.

<span class="mw-page-title-main">Rhodium hexafluoride</span> Chemical compound with formula RhF₆

Rhodium hexafluoride, also rhodium(VI) fluoride, (RhF6) is the inorganic compound of rhodium and fluorine. A black volatile solid, it is a highly reactive material, and a rare example of a rhodium(VI) compound. It is one of seventeen known binary hexafluorides.

<span class="mw-page-title-main">Rhenium hexafluoride</span> Chemical compound

Rhenium hexafluoride, also rhenium(VI) fluoride, (ReF6) is a compound of rhenium and fluorine and one of the seventeen known binary hexafluorides.

Ruthenium hexafluoride, also ruthenium(VI) fluoride (RuF6), is a compound of ruthenium and fluorine and one of the seventeen known binary hexafluorides.

<span class="mw-page-title-main">Osmium hexafluoride</span> Chemical compound

Osmium hexafluoride, also osmium(VI) fluoride, (OsF6) is a compound of osmium and fluorine, and one of the seventeen known binary hexafluorides.

<span class="mw-page-title-main">Uranium hexachloride</span> Chemical compound

Uranium hexachloride (UCl6) is an inorganic chemical compound of uranium in the +6 oxidation state. UCl6 is a metal halide composed of uranium and chlorine. It is a multi-luminescent dark green crystalline solid with a vapor pressure between 1-3 mmHg at 373.15 K. UCl6 is stable in a vacuum, dry air, nitrogen and helium at room temperature. It is soluble in carbon tetrachloride (CCl4). Compared to the other uranium halides, little is known about UCl6.

<span class="mw-page-title-main">Neptunium(VI) fluoride</span> Chemical compound

Neptunium(VI) fluoride (NpF6) is the highest fluoride of neptunium, it is also one of seventeen known binary hexafluorides. It is an orange volatile crystalline solid. It is relatively hard to handle, being very corrosive, volatile and radioactive. Neptunium hexafluoride is stable in dry air but reacts vigorously with water.

Nitride fluorides containing nitride and fluoride ions with the formula NF4-. They can be electronically equivalent to a pair of oxide ions O24-. Nitride fluorides were discovered in 1996 by Lavalle et al. They heated diammonium technetium hexafluoride to 300 °C to yield TcNF. Another preparation is to heat a fluoride compound with a nitride compound in a solid state reaction. The fluorimido ion is F-N2- and is found in a rhenium compound.

References

  1. 1 2 3 4 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.
  2. 1 2 3 Drews, T.; Supeł, J.; Hagenbach, A.; Seppelt, K. (2006). "Solid State Molecular Structures of Transition Metal Hexafluorides". Inorganic Chemistry . 45 (9): 3782–3788. doi:10.1021/ic052029f. PMID   16634614.
  3. 1 2 3 Selig, H.; Chernick, C.L.; Malm, J.G. (1961). "The Preparation and Properties of TcF6". Journal of Inorganic and Nuclear Chemistry. 19 (3–4): 377–381. doi:10.1016/0022-1902(61)80132-2.
  4. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN   978-0-08-037941-8.
  5. ↑ Selig, H.; Cafasso, F. A.; Gruen, D. M.; Malm, J. G. (1962). "Magnetic Susceptibility of ReF6". Journal of Chemical Physics . 36 (12): 3440. Bibcode:1962JChPh..36.3440S. doi:10.1063/1.1732477.
  6. ↑ Howard H. Claassen; Henry Selig & John G. Malm (1962). "Vibrational Spectra of MoF6 and TcF6". Journal of Chemical Physics. 36 (11): 2888–2890. Bibcode:1962JChPh..36.2888C. doi:10.1063/1.1732396.
  7. ↑ Howard H. Claassen; Gordon L. Goodman; John H. Holloway & Henry Selig (1970). "Raman Spectra of MoF6, TcF6, ReF6, UF6, SF6, SeF6, and TeF6 in the Vapor State". Journal of Chemical Physics. 53 (1): 341–348. Bibcode:1970JChPh..53..341C. doi:10.1063/1.1673786.
  8. ↑ Siegel S, Northrop DA (1966). "X-Ray Diffraction Studies of Some Transition Metal Hexafluorides". Inorganic Chemistry. 5 (12): 2187–2188. doi:10.1021/ic50046a025.
  9. ↑ Selig, H; Cafasso, F A.; Gruen, D M.; Malm, J G. (1962). "Magnetic Susceptibility of ReF6". Journal of Chemical Physics. 36 (12): 3440–3444. Bibcode:1962JChPh..36.3440S. doi:10.1063/1.1732477.
  10. ↑ Edwards, A. J.; Hugill, D.; Peacock, R. D. (1963). "New Fluorine Compounds of Technetium". Nature. 200 (4907): 672. Bibcode:1963Natur.200..672E. doi: 10.1038/200672a0 . S2CID   4259399.
  11. ↑ D. Hugill & R. D. Peacock (1966). "Some quinquevalent fluorotechnetates". Journal of the Chemical Society A: 1339–1341. doi:10.1039/J19660001339.
  12. ↑ Frlec B; Selig H & Hyman H.H (1967). "Hydrazinium(+2) Hexafluorometalates(IV) and -(V) in the 4d and 5d Transition Series". Inorganic Chemistry. 6 (10): 1775–1783. doi:10.1021/ic50056a004.
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