Technetium hexafluoride

{{chembox | verifiedrevid = 412172680 | Name = Technetium(VI) fluoride | ImageFile = Technetium-hexafluoride-2D.png | ImageSize = 120 | ImageClass = skin-invert-image | ImageName = | OtherNames = |Section1={{Chembox Identifiers | CASNo_Ref = {{cascite|correct|??}} | CASNo = 13842-93-8 | ChemSpiderID = 57450770 | SMILES = F[Tc](F)(F)(F)(F)F | PubChem = 57470148 | StdInChI=1S/6FH.Tc/h6*1H;/q;;;;;;+6/p-6 | StdInChIKey = PRVOBRCYHYXCMU-UHFFFAOYSA-H }} |Section2={{Chembox Properties | Formula = TcF₆ | MolarMass = 212 g/mol (⁹⁸Tc) | Appearance = golden-yellow crystals<ref name="CRC_HANDBOOK_TcF6"/> | Density = 3,58 g/cm³ (−140 °C), solid<ref name="D_BLOCK_XF6">{{cite journal | last1 = Drews | first1 = T. | last2 = Supeł | first2 = J. | last3 = Hagenbach | first3 = A. | last4 = Seppelt | first4 = K. | year = 2006 | title = Solid State Molecular Structures of Transition Metal Hexafluorides | journal = Inorganic Chemistry | volume = 45 | issue = 9| pages = 3782–3788 | doi = 10.1021/ic052029f | pmid = 16634614 }}</ref> | MeltingPtC = 37.4 | MeltingPt_ref = <ref name="CRC_HANDBOOK_TcF6">''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.&nbsp;4-93.</ref> | BoilingPtC = 55.3 | BoilingPt_ref = <ref name="CRC_HANDBOOK_TcF6"/> }} |Section3={{Chembox Structure | CrystalStruct = cubic }}<!-- | Solubility | |- --> |Section7={{Chembox Hazards }} }}

'''Technetium hexafluoride''' or '''technetium(VI) fluoride''' (TcF₆) is a yellow inorganic compound with a low melting point. It was first identified in 1961.<ref name = "selig1">{{cite journal| title = The Preparation and Properties of TcF₆ |author1=Selig, H. |author2=Chernick, C.L. |author3=Malm, J.G. | year = 1961 | journal = Journal of Inorganic and Nuclear Chemistry | volume = 19 | issue= 3–4 | pages =377–381 | doi=10.1016/0022-1902(61)80132-2 }}</ref> 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.<ref>{{Greenwood&Earnshaw}}</ref> 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.

== Preparation == Technetium hexafluoride is prepared by heating technetium metal with an excess of F₂ at 400&nbsp;°C.<ref name = "selig1"/>

:Tc + 3 {{chem|F|2}} → {{chem|TcF|6}}

== Description == Technetium hexafluoride is a golden-yellow solid at room temperature. Its melting point is 37.4&nbsp;°C and its boiling point is 55.3&nbsp;°C.<ref name="CRC_HANDBOOK_TcF6"/>

Technetium hexafluoride undergoes a solid phase transition at −4.54&nbsp;°C. Above this temperature (measured at 10&nbsp;°C), the solid structure is cubic. Lattice parameters are ''a''&nbsp;=&nbsp;6.16&nbsp;Å. There are two formula units (in this case, discrete molecules) per unit cell, giving a density of 3.02&nbsp;g·cm⁻³. Below this temperature (measured at −19&nbsp;°C), the solid structure is orthorhombic space group ''Pnma''. Lattice parameters are ''a''&nbsp;=&nbsp;9.55&nbsp;Å, ''b''&nbsp;=&nbsp;8.74&nbsp;Å, and ''c''&nbsp;=&nbsp;5.02&nbsp;Å. There are four formula units (in this case, discrete molecules) per unit cell, giving a density of 3.38&nbsp;g·cm⁻³. At −140&nbsp;°C, the solid structure is still orthothombic, but the lattice parameters are now ''a''&nbsp;=&nbsp;9.360&nbsp;Å, ''b''&nbsp;=&nbsp;8.517&nbsp;Å, and ''c''&nbsp;=&nbsp;4.934&nbsp;Å, giving a density of 3.58&nbsp;g·cm⁻³.<ref name="D_BLOCK_XF6"/>

The TcF₆ molecule itself (the form important for the liquid or gas phase) has octahedral molecular geometry, which has point group (''O_h''). The Tc–F bond length is 1.812&nbsp;Å.<ref name="D_BLOCK_XF6"/> Its magnetic moment has been measured to be 0.45 ''μ''_B.<ref>{{cite journal |last1=Selig |first1=H. |last2=Cafasso |first2=F. A. |last3=Gruen |first3=D. M. |author3-link=Dieter M. Gruen |last4=Malm |first4=J. G. |year=1962 |title=Magnetic Susceptibility of ReF₆ |journal=Journal of Chemical Physics |volume=36 |issue=12 |pages= 3440|doi=10.1063/1.1732477|bibcode=1962JChPh..36.3440S }}</ref>

== Properties ==

=== Physical === TcF₆ is octahedral, as shown by infrared and Raman spectra.<ref>{{cite journal| title = Vibrational Spectra of MoF₆ and TcF₆ |author1=Howard H. Claassen |author2=Henry Selig |author3=John G. Malm |name-list-style=amp | journal = Journal of Chemical Physics | volume = 36 | issue = 11 | pages = 2888–2890 | year = 1962 |doi = 10.1063/1.1732396|bibcode=1962JChPh..36.2888C }}</ref><ref>{{cite journal| title = Raman Spectra of MoF₆, TcF₆, ReF₆, UF₆, SF₆, SeF₆, and TeF₆ in the Vapor State |author1=Howard H. Claassen |author2=Gordon L. Goodman |author3=John H. Holloway |author4=Henry Selig |name-list-style=amp | journal = Journal of Chemical Physics | volume = 53 | issue = 1 | pages = 341–348 | year= 1970 | doi=10.1063/1.1673786|bibcode=1970JChPh..53..341C }}</ref> 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.<ref>{{cite journal| title =X-Ray Diffraction Studies of Some Transition Metal Hexafluorides |vauthors=Siegel S, Northrop DA | journal = Inorganic Chemistry | volume = 5 | issue = 12 | pages = 2187–2188 | doi =10.1021/ic50046a025| year =1966}}</ref> Preliminary measurements of magnetic moment yield a value of 0.45 μB, which is lower than expected for a d¹ octahedral compound.<ref>{{cite journal| title = Magnetic Susceptibility of ReF₆ |author1=Selig, H |author2=Cafasso, F A. |author3=Gruen, D M. |author4=Malm, J G. | journal = Journal of Chemical Physics | volume = 36 | issue = 12 | pages = 3440–3444 | doi =10.1063/1.1732477| year = 1962|bibcode=1962JChPh..36.3440S }}</ref>

=== Chemical === TcF₆ reacts with alkaline chlorides in iodine pentafluoride (IF₅) solution to form hexafluorotechnetates.<ref>{{cite journal| title = New Fluorine Compounds of Technetium | journal = Nature| year = 1963| volume = 200| page = 672| doi =10.1038/200672a0| last1 = Edwards| first1 = A. J.| last2 = Hugill| first2 = D.| last3 = Peacock| first3 = R. D.| issue=4907| bibcode = 1963Natur.200..672E| s2cid = 4259399| doi-access = free}}</ref><ref>{{cite journal| title = Some quinquevalent fluorotechnetates |author1=D. Hugill |author2=R. D. Peacock |name-list-style=amp | journal =Journal of the Chemical Society A| year = 1966 | pages = 1339–1341 |doi = 10.1039/J19660001339}}</ref> TcF₆ disproportionates on hydrolysis with aqueous NaOH to form a black precipitate of TcO₂.<ref name = "selig1" /> In hydrogen fluoride solution, TcF₆ reacts with hydrazinium fluoride to yield N₂H₆TcF₆ or N₂H₆(TcF₆)₂.<ref>{{cite journal| title = Hydrazinium(+2) Hexafluorometalates(IV) and -(V) in the 4d and 5d Transition Series |author1=Frlec B |author2=Selig H |author3=Hyman H.H |name-list-style=amp | journal = Inorganic Chemistry | volume = 6 | issue = 10 | year =1967 | pages = 1775–1783 | doi =10.1021/ic50056a004}}</ref>

== References == {{reflist}} {{Hexafluorides}} {{Technetium compounds}} {{fluorine compounds}}

Category:Technetium compounds Category:Hexafluorides Category:Octahedral compounds