Hexafluoride: Difference between revisions
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[[Image:Hexafluorides 17.svg|thumb|250px|Hexafluoride-forming elements]] |
[[Image:Hexafluorides 17.svg|thumb|250px|Hexafluoride-forming elements]] |
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[[Image:Sulfur-hexafluoride-3D-balls.png|thumb|125px|Octahedral structure of SF<sub>6</sub>]] |
[[Image:Sulfur-hexafluoride-3D-balls.png|thumb|125px|Octahedral structure of SF<sub>6</sub>]] |
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Seventeen elements are known to form binary hexafluorides. |
Seventeen elements are known to form binary hexafluorides.<ref name=Seppelt/> Nine of these elements are [[transition metal]]s, three are [[actinide]]s, four are [[chalcogen]]s, and one is a [[noble gas]]. Most hexafluorides are [[molecule|molecular]] compounds with low [[melting point|melting]] and [[boiling point]]s. Four hexafluorides (S, Se, Te, and W) are gases at room temperature (25 °C) and a pressure of 1 [[atmosphere (unit)|atm]], two are liquids (Re, Mo), and the others are volatile solids. The [[group 6 element|group 6]], [[chalcogen]], and [[noble gas]] hexafluorides are colourless, but the other hexafluorides have colours ranging from white, through yellow, orange, red, brown, and grey, to black. |
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The molecular geometry of binary hexafluorides is generally [[octahedral molecular geometry|octahedral]], although some derivatives are distorted from O<sub>h</sub> [[symmetry group|symmetry]]. For the main group hexafluorides, distortion is pronounced for the 14-electron noble gas derivatives. Distortions in gaseous [[Xenon hexafluoride|XeF<sub>6</sub>]] are caused by its non-bonding [[lone pair]], according to [[VSEPR theory]]. In the solid state, it adopts a complex structure involving tetramers and hexamers. According to [[quantum chemical]] calculations, ReF<sub>6</sub> and RuF<sub>6</sub> should have tetragonally distorted structures (where the two bonds along one axis are longer or shorter than the other four), but this has not been verified experimentally.<ref name="D_BLOCK_XF6">{{cite journal |author1=Drews, T. |author2=Supeł, J. |author3=Hagenbach, A. |author4=Seppelt, K. |title= Solid state molecular structures of transition metal hexafluorides |journal= Inorganic Chemistry |year= 2006 |volume= 45 |issue= 9 |pages= 3782–3788 |doi= 10.1021/ic052029f |pmid= 16634614 }}</ref> |
The molecular geometry of binary hexafluorides is generally [[octahedral molecular geometry|octahedral]], although some derivatives are distorted from O<sub>h</sub> [[symmetry group|symmetry]]. For the main group hexafluorides, distortion is pronounced for the 14-electron noble gas derivatives. Distortions in gaseous [[Xenon hexafluoride|XeF<sub>6</sub>]] are caused by its non-bonding [[lone pair]], according to [[VSEPR theory]]. In the solid state, it adopts a complex structure involving tetramers and hexamers. According to [[quantum chemical]] calculations, ReF<sub>6</sub> and RuF<sub>6</sub> should have tetragonally distorted structures (where the two bonds along one axis are longer or shorter than the other four), but this has not been verified experimentally.<ref name="D_BLOCK_XF6">{{cite journal |author1=Drews, T. |author2=Supeł, J. |author3=Hagenbach, A. |author4=Seppelt, K. |title= Solid state molecular structures of transition metal hexafluorides |journal= Inorganic Chemistry |year= 2006 |volume= 45 |issue= 9 |pages= 3782–3788 |doi= 10.1021/ic052029f |pmid= 16634614 }}</ref> |
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[[Polonium hexafluoride]] is known, but not well-studied. It could not be made from <sup>210</sup>Po, but using the longer-lived isotope <sup>208</sup>Po and reacting it with fluorine found a volatile product that is almost certainly PoF<sub>6</sub>.<ref name=Seppelt/> The quoted boiling point in the table below is a prediction. |
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The status of [[polonium hexafluoride]] is unclear: some experimental results suggest that it may have been synthesized, but it was not well characterized. The quoted boiling point in the table below is thus a prediction. Despite this situation, some sources describe it without comment as a known compound. |
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===Binary hexafluorides of the chalcogens=== |
===Binary hexafluorides of the chalcogens=== |
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{| class="wikitable" |
{| class="wikitable" |
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! Compound !! [[Chemical formula|Formula]] !! [[Melting point|m.p]] (°C) !! [[boiling point|b.p.]] (°C) !! [[sublimation point|subl.p.]] (°C) !! [[molar mass|MW]] !! solid [[density|ρ]] (g cm<sup>−3</sup>) (at m.p.)<ref>Wilhelm Klemm and Paul Henkel "Über einige physikalische Eigenschaften von SF<sub>6</sub>, SeF<sub>6</sub>, TeF<sub>6</sub> und CF<sub>4</sub>" Z. anorg. allgem. Chem. 1932, vol. 207, pages 73–86. {{ |
! Compound !! [[Chemical formula|Formula]] !! [[Melting point|m.p]] (°C) !! [[boiling point|b.p.]] (°C) !! [[sublimation point|subl.p.]] (°C) !! [[molar mass|MW]] !! solid [[density|ρ]] (g cm<sup>−3</sup>) (at m.p.)<ref>Wilhelm Klemm and Paul Henkel "Über einige physikalische Eigenschaften von SF<sub>6</sub>, SeF<sub>6</sub>, TeF<sub>6</sub> und CF<sub>4</sub>" Z. anorg. allgem. Chem. 1932, vol. 207, pages 73–86. {{doi|10.1002/zaac.19322070107}}</ref> !! Bond distance ([[picometer|pm]]) !! Colour |
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| [[Sulfur hexafluoride]] || {{chem|SF|6}} || −50.8 || || −63.8 || 146.06 || 2.51 (−50 °C) || 156.4 || colourless |
| [[Sulfur hexafluoride]] || {{chem|SF|6}} || −50.8 || || −63.8 || 146.06 || 2.51 (−50 °C) || 156.4 || colourless |
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| [[Tellurium hexafluoride]]<ref>{{cite book |title= [[CRC Handbook of Chemistry and Physics]] |edition= 90 |publisher= CRC Press |location= Boca Raton, FL |year= 2009 |isbn= 978-1-4200-9084-0 |chapter= 4. Physical Constants of Inorganic Compound |pages= 4–95 }}</ref> || {{chem|TeF|6}} || −38.9 || −37.6 || || 241.59 || 3.76 || 184 || colourless |
| [[Tellurium hexafluoride]]<ref>{{cite book |title= [[CRC Handbook of Chemistry and Physics]] |edition= 90 |publisher= CRC Press |location= Boca Raton, FL |year= 2009 |isbn= 978-1-4200-9084-0 |chapter= 4. Physical Constants of Inorganic Compound |pages= 4–95 }}</ref> || {{chem|TeF|6}} || −38.9 || −37.6 || || 241.59 || 3.76 || 184 || colourless |
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| [[Polonium hexafluoride]]<ref>CAS #35473-38-2</ref><ref name="Holleman&Wiberg">{{Holleman&Wiberg|page=594}}</ref> || {{chem|PoF|6}} || || ≈ −40? || |
| [[Polonium hexafluoride]]<ref>CAS #35473-38-2</ref><ref name="Holleman&Wiberg">{{Holleman&Wiberg|page=594}}</ref> || {{chem|PoF|6}} || || ≈ −40? || || 322.99 || || || colourless<ref name="Holleman&Wiberg"/> |
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! Compound !! [[Chemical formula|Formula]] !! [[Melting point|m.p]] (°C) !! [[boiling point|b.p.]] (°C) !! [[sublimation point|subl.p.]] (°C) !! [[molar mass|MW]] !! solid [[density|ρ]] (g cm<sup>−3</sup>) !! Bond ([[picometer|pm]]) !! Colour |
! Compound !! [[Chemical formula|Formula]] !! [[Melting point|m.p]] (°C) !! [[boiling point|b.p.]] (°C) !! [[sublimation point|subl.p.]] (°C) !! [[molar mass|MW]] !! solid [[density|ρ]] (g cm<sup>−3</sup>) !! Bond ([[picometer|pm]]) !! Colour |
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| [[Xenon hexafluoride]] || {{chem|XeF|6}} || 49.5 || 75.6 || || 245.28 || 3.56 || || colourless (solid)<br>yellow (gas) |
| [[Xenon hexafluoride]] || {{chem|XeF|6}} || 49.5 || 75.6 || || 245.28 || 3.56 || || colourless (solid)<br />yellow (gas) |
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===Applications of binary hexafluorides=== |
===Applications of binary hexafluorides=== |
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Some metal hexafluorides find applications due to their volatility. [[Uranium hexafluoride]] is used in the [[uranium enrichment]] process to produce fuel for [[nuclear reactor]]s. [[Fluoride volatility]] can also be exploited for [[nuclear fuel reprocessing]]. [[Tungsten hexafluoride]] is used in the production of [[semiconductors]] through the process of [[chemical vapor deposition]].<ref>http://www.timedomaincvd.com/CVD_Fundamentals/films/W_WSi.html</ref> |
Some metal hexafluorides find applications due to their volatility. [[Uranium hexafluoride]] is used in the [[uranium enrichment]] process to produce fuel for [[nuclear reactor]]s. [[Fluoride volatility]] can also be exploited for [[nuclear fuel reprocessing]]. [[Tungsten hexafluoride]] is used in the production of [[semiconductors]] through the process of [[chemical vapor deposition]].<ref>{{Cite web |title=Tungsten and Tungsten Silicide Chemical Vapor Deposition |url=http://www.timedomaincvd.com/CVD_Fundamentals/films/W_WSi.html |archive-url=https://web.archive.org/web/20140208223005/http://www.timedomaincvd.com:80/CVD_Fundamentals/films/W_WSi.html |archive-date=2014-02-08 |website=TimeDomain CVD, Inc.}}</ref> |
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===Predicted binary hexafluorides === |
===Predicted binary hexafluorides === |
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====Radon hexafluoride==== |
====Radon hexafluoride==== |
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[[Radon hexafluoride]] ({{chem|RnF|6}}), the heavier homologue of [[xenon hexafluoride]], has been studied theoretically,<ref>{{ cite journal |last1= Filatov |first1= M. |last2= Cremer |first2= D. |title= Bonding in radon hexafluoride: An unusual relativistic problem |journal= Physical Chemistry Chemical Physics |year= 2003 |volume= 2003 |issue= 5 |pages= 1103–1105 |doi= 10.1039/b212460m |bibcode= 2003PCCP....5.1103F }}</ref> but its synthesis has not yet been confirmed. Higher fluorides of radon may have been observed in experiments where unknown radon-containing products distilled together with [[xenon hexafluoride]], and perhaps in the production of radon trioxide: these may have been RnF<sub>4</sub>, RnF<sub>6</sub>, or both.<ref>{{cite journal|author=Stein, L.|date=1970|journal=[[Science (journal)|Science]]|volume =168|doi=10.1126/science.168.3929.362|title=Ionic Radon Solution|pmid=17809133|issue=3929|bibcode=1970Sci...168..362S|pages=362–4|s2cid=31959268}}</ref> It is likely that the difficulty in identifying higher fluorides of radon stems from radon being kinetically hindered from being oxidised beyond the divalent state. This is due to the strong ionicity of [[radon difluoride|RnF<sub>2</sub>]] and the high positive charge on Rn in RnF<sup>+</sup>. Spatial separation of RnF<sub>2</sub> molecules may be necessary to clearly identify higher fluorides of radon, of which RnF<sub>4</sub> is expected to be more stable than RnF<sub>6</sub> due to [[Spin–orbit interaction|spin–orbit]] splitting of the 6p shell of radon (Rn<sup>IV</sup> would have a closed-shell 6s{{su|p=2}}6p{{su|b=1/2|p=2}} configuration).<ref>{{cite journal |last1=Liebman |first1=Joel F. |date=1975 |title=Conceptual Problems in Noble Gas and Fluorine Chemistry, II: The Nonexistence of Radon Tetrafluoride |journal=Inorg. Nucl. Chem. Lett. |volume=11 |issue=10 |pages=683–685 |doi=10.1016/0020-1650(75)80185-1}}</ref> |
[[Radon hexafluoride]] ({{chem|RnF|6}}), the heavier homologue of [[xenon hexafluoride]], has been studied theoretically,<ref>{{ cite journal |last1= Filatov |first1= M. |last2= Cremer |first2= D. |title= Bonding in radon hexafluoride: An unusual relativistic problem |journal= Physical Chemistry Chemical Physics |year= 2003 |volume= 2003 |issue= 5 |pages= 1103–1105 |doi= 10.1039/b212460m |bibcode= 2003PCCP....5.1103F }}</ref> but its synthesis has not yet been confirmed. Higher fluorides of [[radon]] may have been observed in experiments where unknown radon-containing products distilled together with [[xenon hexafluoride]], and perhaps in the production of radon trioxide: these may have been RnF<sub>4</sub>, RnF<sub>6</sub>, or both.<ref>{{cite journal|author=Stein, L.|date=1970|journal=[[Science (journal)|Science]]|volume =168|doi=10.1126/science.168.3929.362|title=Ionic Radon Solution|pmid=17809133|issue=3929|bibcode=1970Sci...168..362S|pages=362–4|s2cid=31959268}}</ref> It is likely that the difficulty in identifying higher fluorides of radon stems from radon being kinetically hindered from being oxidised beyond the divalent state. This is due to the strong ionicity of [[radon difluoride|RnF<sub>2</sub>]] and the high positive charge on Rn in RnF<sup>+</sup>. Spatial separation of RnF<sub>2</sub> molecules may be necessary to clearly identify higher fluorides of radon, of which RnF<sub>4</sub> is expected to be more stable than RnF<sub>6</sub> due to [[Spin–orbit interaction|spin–orbit]] splitting of the 6p shell of radon (Rn<sup>IV</sup> would have a closed-shell 6s{{su|p=2}}6p{{su|b=1/2|p=2}} configuration).<ref>{{cite journal |last1=Liebman |first1=Joel F. |date=1975 |title=Conceptual Problems in Noble Gas and Fluorine Chemistry, II: The Nonexistence of Radon Tetrafluoride |journal=Inorg. Nucl. Chem. Lett. |volume=11 |issue=10 |pages=683–685 |doi=10.1016/0020-1650(75)80185-1}}</ref> The ionicity of the Rn–F bond may also result in a strongly fluorine-bridged structure in the solid, so that radon fluorides may not be volatile.<ref name=Seppelt/> Continuing the trend, the heavier [[oganesson]] hexafluoride should be unbound.<ref name=Seppelt/> |
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====Others==== |
====Others==== |
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[[Krypton hexafluoride]] ({{chem|KrF|6}}) has been predicted to be stable, but has not been synthesised due to the extreme difficulty of oxidising krypton beyond Kr(II).<ref>{{Cite journal | last1 = Dixon | first1 = D. A. | last2 = Wang | first2 = T. H. | last3 = Grant | first3 = D. J. | last4 = Peterson | first4 = K. A. | last5 = Christe | first5 = K. O. | last6 = Schrobilgen | first6 = G. J. | title = Heats of Formation of Krypton Fluorides and Stability Predictions for KrF<sub>4</sub> and KrF<sub>6</sub> from High Level Electronic Structure Calculations | journal = Inorganic Chemistry | volume = 46 | issue = 23 | pages = 10016–10021 | year = 2007 | pmid = 17941630 | doi = 10.1021/ic701313h}}</ref> The synthesis of [[americium hexafluoride]] ({{chem|AmF|6}}) by the [[Halogenation#Fluorination|fluorination]] of [[americium(IV) fluoride]] ({{chem|AmF|4}}) was attempted in 1990,<ref>{{cite journal |last1= Malm |first1= J. G. |last2= Weinstock |first2= B. |last3= Weaver |first3= E. E. |title= The Preparation and Properties of NpF<sub>6</sub>; a Comparison with PuF<sub>6</sub> |journal= The Journal of Physical Chemistry |year= 1958 |volume= 62 |issue= 12 |pages= 1506–1508 |doi= 10.1021/j150570a009 }}</ref> but was unsuccessful; there have also been possible thermochromatographic identifications of it and [[curium hexafluoride]] (CmF<sub>6</sub>), but it is debated if these are conclusive.<ref name=Seppelt/> [[Palladium hexafluoride]] ({{chem|PdF|6}}), the lighter homologue of [[platinum hexafluoride]], has been calculated to be stable,<ref>{{cite journal |last1= Aullón |first1= G. |last2= Alvarez |first2= S. |title= On the Existence of Molecular Palladium(VI) Compounds: Palladium Hexafluoride |journal= [[Inorganic Chemistry (journal)|Inorganic Chemistry]] |year= 2007 |volume= 46 |issue= 7 |pages= 2700–2703 |doi= 10.1021/ic0623819 |pmid= 17326630 }}</ref> but has not yet been produced; the possibility of [[silver hexafluoride|silver]] (AgF<sub>6</sub>) and [[gold hexafluoride]]s (AuF<sub>6</sub>) has also been discussed.<ref name=Seppelt>{{cite journal |last1=Seppelt |first1=Konrad |date=2015 |title=Molecular Hexafluorides |journal=Chemical Reviews |volume=115 |issue=2 |pages=1296–1306 |doi=10.1021/cr5001783|pmid=25418862 }}</ref> [[Chromium hexafluoride]] ({{chem|CrF|6}}), the lighter homologue of [[molybdenum hexafluoride]] and [[tungsten hexafluoride]], was reported, but has been shown to be a mistaken identification of the known [[Chromium pentafluoride|pentafluoride]] ({{chem|CrF|5}}).<ref>{{cite journal|last1=Riedel |first1=S. |last2=Kaupp |first2=M. |title=The highest oxidation states of the transition metal elements |journal=Coordination Chemistry Reviews |year=2009 |volume=253 |issue=5–6 |doi=10.1016/j.ccr.2008.07.014 |pages=606–624 |
[[Krypton hexafluoride]] ({{chem|KrF|6}}) has been predicted to be stable, but has not been synthesised due to the extreme difficulty of oxidising [[krypton]] beyond Kr(II).<ref>{{Cite journal | last1 = Dixon | first1 = D. A. | last2 = Wang | first2 = T. H. | last3 = Grant | first3 = D. J. | last4 = Peterson | first4 = K. A. | last5 = Christe | first5 = K. O. | last6 = Schrobilgen | first6 = G. J. | title = Heats of Formation of Krypton Fluorides and Stability Predictions for KrF<sub>4</sub> and KrF<sub>6</sub> from High Level Electronic Structure Calculations | journal = Inorganic Chemistry | volume = 46 | issue = 23 | pages = 10016–10021 | year = 2007 | pmid = 17941630 | doi = 10.1021/ic701313h}}</ref> The synthesis of [[americium hexafluoride]] ({{chem|AmF|6}}) by the [[Halogenation#Fluorination|fluorination]] of [[americium(IV) fluoride]] ({{chem|AmF|4}}) was attempted in 1990,<ref>{{cite journal |last1= Malm |first1= J. G. |last2= Weinstock |first2= B. |last3= Weaver |first3= E. E. |title= The Preparation and Properties of NpF<sub>6</sub>; a Comparison with PuF<sub>6</sub> |journal= The Journal of Physical Chemistry |year= 1958 |volume= 62 |issue= 12 |pages= 1506–1508 |doi= 10.1021/j150570a009 }}</ref> but was unsuccessful; there have also been possible thermochromatographic identifications of it and [[curium hexafluoride]] (CmF<sub>6</sub>), but it is debated if these are conclusive.<ref name=Seppelt/> [[Palladium hexafluoride]] ({{chem|PdF|6}}), the lighter homologue of [[platinum hexafluoride]], has been calculated to be stable,<ref>{{cite journal |last1= Aullón |first1= G. |last2= Alvarez |first2= S. |title= On the Existence of Molecular Palladium(VI) Compounds: Palladium Hexafluoride |journal= [[Inorganic Chemistry (journal)|Inorganic Chemistry]] |year= 2007 |volume= 46 |issue= 7 |pages= 2700–2703 |doi= 10.1021/ic0623819 |pmid= 17326630 }}</ref> but has not yet been produced; the possibility of [[silver hexafluoride|silver]] (AgF<sub>6</sub>) and [[gold hexafluoride]]s (AuF<sub>6</sub>) has also been discussed.<ref name=Seppelt>{{cite journal |last1=Seppelt |first1=Konrad |date=2015 |title=Molecular Hexafluorides |journal=Chemical Reviews |volume=115 |issue=2 |pages=1296–1306 |doi=10.1021/cr5001783|pmid=25418862 }}</ref> [[Chromium hexafluoride]] ({{chem|CrF|6}}), the lighter homologue of [[molybdenum hexafluoride]] and [[tungsten hexafluoride]], was reported, but has been shown to be a mistaken identification of the known [[Chromium pentafluoride|pentafluoride]] ({{chem|CrF|5}}).<ref>{{cite journal|last1=Riedel |first1=S. |last2=Kaupp |first2=M. |title=The highest oxidation states of the transition metal elements |journal=Coordination Chemistry Reviews |year=2009 |volume=253 |issue=5–6 |doi=10.1016/j.ccr.2008.07.014 |pages=606–624}}</ref> |
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== Literature == |
== Literature == |
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* {{cite journal |author1=Galkin, N. P. |author2=Tumanov, Yu. N. |title= Reactivity and Thermal Stability of Hexafluorides |journal= Russian Chemical Reviews |year= 1971 |volume= 40 |issue= 2 |pages= 154–164 |url= http://www.turpion.org/php/paper.phtml?journal_id=rc&paper_id=1902 |doi= 10.1070/RC1971v040n02ABEH001902 |bibcode= 1971RuCRv..40..154G }} |
* {{cite journal |author1= Galkin, N. P. |author2= Tumanov, Yu. N. |title= Reactivity and Thermal Stability of Hexafluorides |journal= Russian Chemical Reviews |year= 1971 |volume= 40 |issue= 2 |pages= 154–164 |url= http://www.turpion.org/php/paper.phtml?journal_id=rc&paper_id=1902 |doi= 10.1070/RC1971v040n02ABEH001902 |bibcode= 1971RuCRv..40..154G |s2cid= 250901336 |access-date= 2012-05-12 |archive-date= 2015-11-30 |archive-url= https://web.archive.org/web/20151130091739/http://www.turpion.org/php/paper.phtml?journal_id=rc&paper_id=1902 |url-status= dead }} |
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== References == |
== References == |
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==Sources== |
==Sources== |
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*{{cite book|last1=Wiberg |first1= Egon |last2= Wiberg |first2=Nils |last3=Holleman |first3=Arnold Frederick|title=Inorganic chemistry|url=https://books.google.com/books?id=Mtth5g59dEIC|access-date=3 March 2011|year=2001|publisher=Academic Press|isbn=978-0-12-352651-9}} |
*{{cite book|last1=Wiberg |first1= Egon |last2= Wiberg |first2=Nils |last3=Holleman |first3=Arnold Frederick|title=Inorganic chemistry|url=https://books.google.com/books?id=Mtth5g59dEIC|access-date=3 March 2011|year=2001|publisher=Academic Press|isbn=978-0-12-352651-9}} |
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{{Commons category|Hexafluorides}} |
{{Commons category|Hexafluorides}} |
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Latest revision as of 13:53, 29 July 2024
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.
Hexafluoride cations
[edit]Cationic hexafluorides exist but are rarer than neutral or anionic hexafluorides. Examples are the hexafluorochlorine (ClF6+), and hexafluorobromine (BrF6+) cations.[1]
Hexafluoride anions
[edit]
Many elements form anionic hexafluorides. Members of commercial interest are hexafluorophosphate (PF6−) and hexafluorosilicate (SiF62−).
Many transition metals form hexafluoride anions. Often the monoanions are generated by reduction of the neutral hexafluorides. For example, PtF6− arises by reduction of PtF6 by O2. Because of its highly basic nature and its resistance to oxidation, the fluoride ligand stabilizes some metals in otherwise rare high oxidation states, such as hexafluorocuprate(IV), CuF2−6 and hexafluoronickelate(IV), NiF2−6.
Binary hexafluorides
[edit]
Seventeen elements are known to form binary hexafluorides.[2] Nine of these elements are transition metals, three are actinides, four are chalcogens, and one is a noble gas. Most hexafluorides are molecular compounds with low melting and boiling points. Four hexafluorides (S, Se, Te, and W) are gases at room temperature (25 °C) and a pressure of 1 atm, two are liquids (Re, Mo), and the others are volatile solids. The group 6, chalcogen, and noble gas hexafluorides are colourless, but the other hexafluorides have colours ranging from white, through yellow, orange, red, brown, and grey, to black.
The molecular geometry of binary hexafluorides is generally octahedral, although some derivatives are distorted from Oh symmetry. For the main group hexafluorides, distortion is pronounced for the 14-electron noble gas derivatives. Distortions in gaseous XeF6 are caused by its non-bonding lone pair, according to VSEPR theory. In the solid state, it adopts a complex structure involving tetramers and hexamers. According to quantum chemical calculations, ReF6 and RuF6 should have tetragonally distorted structures (where the two bonds along one axis are longer or shorter than the other four), but this has not been verified experimentally.[3]
Polonium hexafluoride is known, but not well-studied. It could not be made from 210Po, but using the longer-lived isotope 208Po and reacting it with fluorine found a volatile product that is almost certainly PoF6.[2] The quoted boiling point in the table below is a prediction.
Binary hexafluorides of the chalcogens
[edit]| Compound | Formula | m.p (°C) | b.p. (°C) | subl.p. (°C) | MW | solid ρ (g cm−3) (at m.p.)[4] | Bond distance (pm) | Colour |
|---|---|---|---|---|---|---|---|---|
| Sulfur hexafluoride | SF 6 |
−50.8 | −63.8 | 146.06 | 2.51 (−50 °C) | 156.4 | colourless | |
| Selenium hexafluoride | SeF 6 |
−34.6 | −46.6 | 192.95 | 3.27 | 167–170 | colourless | |
| Tellurium hexafluoride[5] | TeF 6 |
−38.9 | −37.6 | 241.59 | 3.76 | 184 | colourless | |
| Polonium hexafluoride[6][7] | PoF 6 |
≈ −40? | 322.99 | colourless[7] |
Binary hexafluorides of the noble gases
[edit]| Compound | Formula | m.p (°C) | b.p. (°C) | subl.p. (°C) | MW | solid ρ (g cm−3) | Bond (pm) | Colour |
|---|---|---|---|---|---|---|---|---|
| Xenon hexafluoride | XeF 6 |
49.5 | 75.6 | 245.28 | 3.56 | colourless (solid) yellow (gas) |
Binary hexafluorides of the transition metals
[edit]| Compound | Formula | m.p (°C) | b.p. (°C) | subl.p. (°C) | MW | solid ρ (g cm−3) | Bond (pm) | Colour |
|---|---|---|---|---|---|---|---|---|
| Molybdenum hexafluoride | MoF 6 |
17.5 | 34.0 | 209.94 | 3.50 (−140 °C)[3] | 181.7[3] | colourless | |
| Technetium hexafluoride | TcF 6 |
37.4 | 55.3 | (212) | 3.58 (−140 °C)[3] | 181.2[3] | yellow | |
| Ruthenium hexafluoride | RuF 6 |
54 | 215.07 | 3.68 (−140 °C)[3] | 181.8[3] | dark brown | ||
| Rhodium hexafluoride | RhF 6 |
≈ 70 | 216.91 | 3.71 (−140 °C)[3] | 182.4[3] | black | ||
| Tungsten hexafluoride | WF 6 |
2.3 | 17.1 | 297.85 | 4.86 (−140 °C)[3] | 182.6[3] | colourless | |
| Rhenium hexafluoride | ReF 6 |
18.5 | 33.7 | 300.20 | 4.94 (−140 °C)[3] | 182.3[3] | yellow | |
| Osmium hexafluoride | OsF 6 |
33.4 | 47.5 | 304.22 | 5.09 (−140 °C)[3] | 182.9[3] | yellow | |
| Iridium hexafluoride | IrF 6 |
44 | 53.6 | 306.21 | 5.11 (−140 °C)[3] | 183.4[3] | yellow | |
| Platinum hexafluoride | PtF 6 |
61.3 | 69.1 | 309.07 | 5.21 (−140 °C)[3] | 184.8[3] | deep red |
Binary hexafluorides of the actinides
[edit]| Compound | Formula | m.p (°C) | b.p. (°C) | subl.p. (°C) | MW | solid ρ (g cm−3) | Bond (pm) | Colour |
|---|---|---|---|---|---|---|---|---|
| Uranium hexafluoride | UF 6 |
64.052 | 56.5 | 351.99 | 5.09 | 199.6 | colorless | |
| Neptunium hexafluoride | NpF 6 |
54.4 | 55.18 | (351) | 198.1 | orange | ||
| Plutonium hexafluoride | PuF 6 |
52 | 62 | (358) | 5.08 | 197.1 | brown |
Chemical properties of binary hexafluorides
[edit]The hexafluorides have a wide range of chemical reactivity. Sulfur hexafluoride is nearly inert and non-toxic due to steric hindrance (the six fluorine atoms are arranged so tightly around the sulfur atom that it is extremely difficult to attack the bonds between the fluorine and sulfur atoms). It has several applications due to its stability, dielectric properties, and high density. Selenium hexafluoride is nearly as unreactive as SF6, but tellurium hexafluoride is not very stable and can be hydrolyzed by water within 1 day. Also, both selenium hexafluoride and tellurium hexafluoride are toxic, while sulfur hexafluoride is non-toxic. In contrast, metal hexafluorides are corrosive, readily hydrolyzed, and may react violently with water. Some of them can be used as fluorinating agents. The metal hexafluorides have a high electron affinity, which makes them strong oxidizing agents.[8] Platinum hexafluoride in particular is notable for its ability to oxidize the dioxygen molecule, O2, to form dioxygenyl hexafluoroplatinate, and for being the first compound that was observed to react with xenon (see xenon hexafluoroplatinate).
Applications of binary hexafluorides
[edit]Some metal hexafluorides find applications due to their volatility. Uranium hexafluoride is used in the uranium enrichment process to produce fuel for nuclear reactors. Fluoride volatility can also be exploited for nuclear fuel reprocessing. Tungsten hexafluoride is used in the production of semiconductors through the process of chemical vapor deposition.[9]
Predicted binary hexafluorides
[edit]Radon hexafluoride
[edit]Radon hexafluoride (RnF
6), the heavier homologue of xenon hexafluoride, has been studied theoretically,[10] but its synthesis has not yet been confirmed. Higher fluorides of radon may have been observed in experiments where unknown radon-containing products distilled together with xenon hexafluoride, and perhaps in the production of radon trioxide: these may have been RnF4, RnF6, or both.[11] It is likely that the difficulty in identifying higher fluorides of radon stems from radon being kinetically hindered from being oxidised beyond the divalent state. This is due to the strong ionicity of RnF2 and the high positive charge on Rn in RnF+. Spatial separation of RnF2 molecules may be necessary to clearly identify higher fluorides of radon, of which RnF4 is expected to be more stable than RnF6 due to spin–orbit splitting of the 6p shell of radon (RnIV would have a closed-shell 6s2
6p2
1/2 configuration).[12] The ionicity of the Rn–F bond may also result in a strongly fluorine-bridged structure in the solid, so that radon fluorides may not be volatile.[2] Continuing the trend, the heavier oganesson hexafluoride should be unbound.[2]
Others
[edit]Krypton hexafluoride (KrF
6) has been predicted to be stable, but has not been synthesised due to the extreme difficulty of oxidising krypton beyond Kr(II).[13] The synthesis of americium hexafluoride (AmF
6) by the fluorination of americium(IV) fluoride (AmF
4) was attempted in 1990,[14] but was unsuccessful; there have also been possible thermochromatographic identifications of it and curium hexafluoride (CmF6), but it is debated if these are conclusive.[2] Palladium hexafluoride (PdF
6), the lighter homologue of platinum hexafluoride, has been calculated to be stable,[15] but has not yet been produced; the possibility of silver (AgF6) and gold hexafluorides (AuF6) has also been discussed.[2] Chromium hexafluoride (CrF
6), the lighter homologue of molybdenum hexafluoride and tungsten hexafluoride, was reported, but has been shown to be a mistaken identification of the known pentafluoride (CrF
5).[16]
Literature
[edit]- Galkin, N. P.; Tumanov, Yu. N. (1971). "Reactivity and Thermal Stability of Hexafluorides". Russian Chemical Reviews. 40 (2): 154–164. Bibcode:1971RuCRv..40..154G. doi:10.1070/RC1971v040n02ABEH001902. S2CID 250901336. Archived from the original on 2015-11-30. Retrieved 2012-05-12.
References
[edit]- ^ Wiberg, Wiberg & Holleman 2001, p. 436.
- ^ a b c d e f Seppelt, Konrad (2015). "Molecular Hexafluorides". Chemical Reviews. 115 (2): 1296–1306. doi:10.1021/cr5001783. PMID 25418862.
- ^ a b c d e f g h i j k l m n o p q r s 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.
- ^ Wilhelm Klemm and Paul Henkel "Über einige physikalische Eigenschaften von SF6, SeF6, TeF6 und CF4" Z. anorg. allgem. Chem. 1932, vol. 207, pages 73–86. doi:10.1002/zaac.19322070107
- ^ "4. Physical Constants of Inorganic Compound". CRC Handbook of Chemistry and Physics (90 ed.). Boca Raton, FL: CRC Press. 2009. pp. 4–95. ISBN 978-1-4200-9084-0.
- ^ CAS #35473-38-2
- ^ a b Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, p. 594, ISBN 0-12-352651-5
- ^ Bartlett, N. (1968). "The Oxidizing Properties of the Third Transition Series Hexafluorides and Related Compounds". Angewandte Chemie International Edition. 7 (6): 433–439. doi:10.1002/anie.196804331.
- ^ "Tungsten and Tungsten Silicide Chemical Vapor Deposition". TimeDomain CVD, Inc. Archived from the original on 2014-02-08.
- ^ Filatov, M.; Cremer, D. (2003). "Bonding in radon hexafluoride: An unusual relativistic problem". Physical Chemistry Chemical Physics. 2003 (5): 1103–1105. Bibcode:2003PCCP....5.1103F. doi:10.1039/b212460m.
- ^ Stein, L. (1970). "Ionic Radon Solution". Science. 168 (3929): 362–4. Bibcode:1970Sci...168..362S. doi:10.1126/science.168.3929.362. PMID 17809133. S2CID 31959268.
- ^ Liebman, Joel F. (1975). "Conceptual Problems in Noble Gas and Fluorine Chemistry, II: The Nonexistence of Radon Tetrafluoride". Inorg. Nucl. Chem. Lett. 11 (10): 683–685. doi:10.1016/0020-1650(75)80185-1.
- ^ Dixon, D. A.; Wang, T. H.; Grant, D. J.; Peterson, K. A.; Christe, K. O.; Schrobilgen, G. J. (2007). "Heats of Formation of Krypton Fluorides and Stability Predictions for KrF4 and KrF6 from High Level Electronic Structure Calculations". Inorganic Chemistry. 46 (23): 10016–10021. doi:10.1021/ic701313h. PMID 17941630.
- ^ Malm, J. G.; Weinstock, B.; Weaver, E. E. (1958). "The Preparation and Properties of NpF6; a Comparison with PuF6". The Journal of Physical Chemistry. 62 (12): 1506–1508. doi:10.1021/j150570a009.
- ^ Aullón, G.; Alvarez, S. (2007). "On the Existence of Molecular Palladium(VI) Compounds: Palladium Hexafluoride". Inorganic Chemistry. 46 (7): 2700–2703. doi:10.1021/ic0623819. PMID 17326630.
- ^ Riedel, S.; Kaupp, M. (2009). "The highest oxidation states of the transition metal elements". Coordination Chemistry Reviews. 253 (5–6): 606–624. doi:10.1016/j.ccr.2008.07.014.
Sources
[edit]- Wiberg, Egon; Wiberg, Nils; Holleman, Arnold Frederick (2001). Inorganic chemistry. Academic Press. ISBN 978-0-12-352651-9. Retrieved 3 March 2011.
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