Difference between revisions of "Manganese tetrafluoride"

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Manganese tetrafluoride is in [[Chemical equilibrium| equilibrium]] with [[manganese(III) fluoride]] and elemental [[fluorine]]:
 
Manganese tetrafluoride is in [[Chemical equilibrium| equilibrium]] with [[manganese(III) fluoride]] and elemental [[fluorine]]:
 
:MnF<sub>4</sub> {{eqm}} MnF<sub>3</sub> + ½ F<sub>2</sub>
 
:MnF<sub>4</sub> {{eqm}} MnF<sub>3</sub> + ½ F<sub>2</sub>
−
Decomposition is favoured by increasing temperature, and disfavoured by the presence of fluorine gas, but the exact parameters of the equilibrium are unclear, with some sources saying that MnF<sub>4</sub> will decompose slowly at room temperature,<ref>{{Cotton&Wilkinson4th|page=745}}.</ref><ref>{{Housecroft&Sharpe|page=710}}.</ref> others placing a practical lower temperature limit of 70&nbsp;°C,<ref name="AstorPrepn"/> and another claiming that MnF<sub>4</sub> is essentially stable up to 320&nbsp;°C.<ref>{{citation | first1 = M. | last1 = Adelhelm | first2 = E. | last2 = Jacob | title = MnF<sub>4</sub>: preparation and properties | journal = J. Fluorine Chem. | volume = 54 | issue = 1–3 | year = 1991 | page = 21 | doi = 10.1016/S0022-1139(00)83531-9}}.</ref> The equilibrium pressure of fluorine above MnF<sub>4</sub> at room temperature has been estimated at about 10<sup>−4</sup>&nbsp;Pa (10<sup>−9</sup>&nbsp;bar), and the enthalpy change of reaction at {{nowrap|+44(8) kJ mol<sup>−1</sup>}}.<ref>{{citation | first1 = T. C. | last1 = Ehlert | first2 = M. | last2 = Hsia | title = Mass spectrometric and thermochemical studies of the manganese fluorides | journal = J. Fluorine Chem. | volume = 2 | issue = 1 | year = 1972 | pages = 33–51 | doi = 10.1016/S0022-1139(00)83113-9}}.</ref>{{#tag:ref|These two results are inconsistent with one another, as Δ<sub>r</sub>''H''<sup><s>o</s></sup> would have to be about {{nowrap|+80 kJ mol<sup>−1</sup>}} for ''p''<sub>eq</sup>(F<sub>2</sub>)&nbsp;≈ 10<sup>−9</sup>&nbsp;bar at 298&nbsp;K, given that the overwhelming contribution to Δ<sub>r</sub>''S''<sup><s>o</s></sup> is ''S''<sup><s>o</s></sup>(F<sub>2</sub>)&nbsp;= {{nowrap|202.791(5) J K<sup>−1</sup> mol<sup>−1</sup>}}.<ref>{{CODATA thermo}}.</ref> The quoted value of Δ<sub>r</sub>''H''<sup><s>o</s></sup> is consistent with most reported decomposition temperatures.|group=Note}}
+
Decomposition is favoured by increasing temperature, and disfavoured by the presence of fluorine gas, but the exact parameters of the equilibrium are unclear, with some sources saying that MnF<sub>4</sub> will decompose slowly at room temperature,<ref>{{Cotton&Wilkinson4th|page=745}}.</ref><ref>{{Housecroft&Sharpe|page=710}}.</ref> others placing a practical lower temperature limit of 70&nbsp;°C,<ref name="AstorPrepn"/> and another claiming that MnF<sub>4</sub> is essentially stable up to 320&nbsp;°C.<ref>{{citation | first1 = M. | last1 = Adelhelm | first2 = E. | last2 = Jacob | title = MnF<sub>4</sub>: preparation and properties | journal = J. Fluorine Chem. | volume = 54 | issue = 1–3 | year = 1991 | page = 21 | doi = 10.1016/S0022-1139(00)83531-9}}.</ref> The equilibrium pressure of fluorine above MnF<sub>4</sub> at room temperature has been estimated at about 10<sup>−4</sup>&nbsp;Pa (10<sup>−9</sup>&nbsp;bar), and the enthalpy change of reaction at {{nowrap|+44(8) kJ mol<sup>−1</sup>}}.<ref>{{citation | first1 = T. C. | last1 = Ehlert | first2 = M. | last2 = Hsia | title = Mass spectrometric and thermochemical studies of the manganese fluorides | journal = J. Fluorine Chem. | volume = 2 | issue = 1 | year = 1972 | pages = 33–51 | doi = 10.1016/S0022-1139(00)83113-9}}.</ref>{{#tag:ref|These two results are inconsistent with one another, as Δ<sub>r</sub>''H''<sup><s>o</s></sup> would have to be about {{nowrap|+80 kJ mol<sup>−1</sup>}} for ''p''<sub>eq</sub>(F<sub>2</sub>)&nbsp;≈ 10<sup>−9</sup>&nbsp;bar at 298&nbsp;K, given that the overwhelming contribution to Δ<sub>r</sub>''S''<sup><s>o</s></sup> is ''S''<sup><s>o</s></sup>(F<sub>2</sub>)&nbsp;= {{nowrap|202.791(5) J K<sup>−1</sup> mol<sup>−1</sup>}}.<ref>{{CODATA thermo}}.</ref> The quoted value of Δ<sub>r</sub>''H''<sup><s>o</s></sup> is consistent with most reported decomposition temperatures.|group=Note}}
  
 
===Other reactions===
 
===Other reactions===

Revision as of 11:05, 12 September 2010

Manganese tetrafluoride
IUPAC name manganese tetrafluoride
Other names manganese(IV) fluoride
Identifiers
InChI InChI=1/4FH.Mn/h4*1H;/q;;;;+4/p-4
Standard InChI InChI=1S/4FH.Mn/h4*1H;/q;;;;+4/p-4
Standard InChIKey KWKYNMDHPVYLQQ-UHFFFAOYSA-J
CAS number [15195-58-1]
Properties
Chemical formula MnF4
Molar mass 130.93 g mol−1
Appearance blue solid
Melting point

70 °C decomp.

Solubility in water reacts violently
Related compounds
Other cations Manganese(II) fluoride
Manganese(III) fluoride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Manganese tetrafluoride, MnF4, is the highest fluoride of manganese. It is used as a powerful oxidizing agent and as a means of purifying elemental fluorine.[1][2]

Preparation

Manganese tetrafluoride was first unequivocally prepared in 1961[Note 1] by the reaction of manganese(II) fluoride (or other MnII compounds) with a stream of fluorine gas at 550 °C: the MnF4 sublimes into the gas stream and condenses onto a cold finger.[5][6] This is still the commonest method of preparation, although the sublimation can be avoided by operating at increased fluorine pressure (4.5–6 bar at 180–320 °C) and mechanically agitating the powder to avoid sintering of the grains.[1][7] The reaction can also be carried out starting from manganese powder in a fluidized bed.[8][9]

Other preparations of MnF4 include the fluorination of MnF2 with krypton difluoride,[10] or with F2 in liquid hydrogen fluoride solution under ultraviolet light.[11] Manganese tetrafluoride has also been prepared (but not isolated) in an acid–base reaction between antimony pentafluoride and K2MnF6 as part of a chemical synthesis of elemental fluorine.[12]

K2MnF6 + 2 SbF5 → MnF4 + 2 KSbF6

Chemistry

Decomposition

Manganese tetrafluoride is in equilibrium with manganese(III) fluoride and elemental fluorine:

MnF4 ⇌ MnF3 + ½ F2

Decomposition is favoured by increasing temperature, and disfavoured by the presence of fluorine gas, but the exact parameters of the equilibrium are unclear, with some sources saying that MnF4 will decompose slowly at room temperature,[13][14] others placing a practical lower temperature limit of 70 °C,[1] and another claiming that MnF4 is essentially stable up to 320 °C.[15] The equilibrium pressure of fluorine above MnF4 at room temperature has been estimated at about 10−4 Pa (10−9 bar), and the enthalpy change of reaction at +44(8) kJ mol−1.[16][Note 2]

Other reactions

Manganese tetrafluoride reacts violently with water and even with sodium dried petroleum ether. It immediately decomposes on contact with moist air.

Reaction with alkali metal fluorides or concentrated hydrofluoric acid gives the yellow hexafluoromanganate(IV) anion [MnF6]2−.

Applications

Fluoromanganate(IV) complexes

Notes and references

Notes

  1. ↑ Reports of the preparation of MnF4 date back to the nineteenth century,[3] but are inconsistent with the now-known chemistry of the genuine compound. However, the more stable hexafluoromanganate(IV) compounds were prepared as early as 1899.[4]
  2. ↑ These two results are inconsistent with one another, as ΔrHo would have to be about +80 kJ mol−1 for peq(F2) ≈ 10−9 bar at 298 K, given that the overwhelming contribution to ΔrSo is So(F2) = 202.791(5) J K−1 mol−1.[17] The quoted value of ΔrHo is consistent with most reported decomposition temperatures.

References

  1. ↑ 1.0 1.1 1.2 Torisu, Junichi; Oka, Masakazu; Kuznetsov, Andrey Sergeyevich, et al. (Astor Electronics/Showa Denko) Method of manufacturing manganese tetrafluoride. WO PCT Appl. 2006033480, published 30 March 2006.
  2. ↑ Seseke-Koyro, Ulrich; Garcia-Juan, Placido; Palsherm, Stefan, et al. (Solvay Fluor) Process for the purification of elemental fluorine. WO PCT Appl. 2009074562, published 18 June 2009.
  3. ↑ Melville, W. H. Contribution towards the History of the Fluorides of Manganese. Proc. Am. Acad. Arts Sci. 1876, 12, 228–34, <http://www.jstor.org/stable/25138452>.
  4. ↑ Weinland, R. F.; Lauenstein, O. Z. Anorg. Allg. Chem. 1899, 20, 40.
  5. ↑ Hoppe, Rudolf; Dähne, Wolfgang; Klemm, Wilhelm Mangantetrafluorid, MnF4. Naturwissenschaften 1961, 48 (11), 429. DOI: 10.1007/BF00621676.
  6. ↑ Hoppe, Rudolf; Dähne, Wolfgang; Klemm, Wilhelm Mangantetrafluorid mit einem Anhang über LiMnF5 und LiMnF4. Justus Liebigs Ann. Chem. 1962, 658 (1), 1–5. DOI: 10.1002/jlac.19626580102.
  7. ↑ Seseke-Koyro, Ulrich; Garcia-Juan, Placido; Palsherm, Stefan, et al. (Solvay Fluor) Method for preparing manganese tetrafluoride. WO PCT Appl. 2009074560, published 18 June 2009.
  8. ↑ Roesky, H.; Glemser, O. A New Preparation of Manganese Tetrafluoride. Angew. Chem., Int. Ed. Engl. 1963, 2 (10), 626. DOI: 10.1002/anie.196306262.
  9. ↑ Roesky, Herbert W.; Glemser, Oskar; Hellberg, Karl-Heinz Darstellung von Metallfluoriden in der Wirbelschicht. Chem. Ber. 1965, 98 (6), 2046–48. DOI: 10.1002/cber.19650980642.
  10. ↑ Lutar, Karel; Jesih, Adolf; Žemva, Boris KrF2/MnF4 adducts from KrF2/MnF2 interaction in HF as a route to high purity MnF4. Polyhedron 1988, 7 (13), 1217–19. DOI: 10.1016/S0277-5387(00)81212-7.
  11. ↑ Mazej, Z. Room temperature syntheses of MnF3, MnF4 and hexafluoromanganete(IV) salts of alkali cations. J. Fluorine Chem. 2002, 114 (1), 75–80. DOI: 10.1016/S0022-1139(01)00566-8.
  12. ↑ Christe, Karl O. Chemical synthesis of elemental fluorine. Inorg. Chem. 1986, 25 (21), 3721–24. DOI: 10.1021/ic00241a001.
  13. ↑ Cotton, F. Albert; Wilkinson, Geoffrey Advanced Inorganic Chemistry, 4th ed.; Wiley: New York, 1980; p 745. ISBN 0-471-02775-8.
  14. ↑ Housecroft, Catherine E.; Sharpe, Alan G. Inorganic Chemistry, 3rd ed.; Prentice Hall: New York, 2007; p 710. ISBN 0131755536.
  15. ↑ Adelhelm, M.; Jacob, E. MnF4: preparation and properties. J. Fluorine Chem. 1991, 54 (1–3), 21. DOI: 10.1016/S0022-1139(00)83531-9.
  16. ↑ Ehlert, T. C.; Hsia, M. Mass spectrometric and thermochemical studies of the manganese fluorides. J. Fluorine Chem. 1972, 2 (1), 33–51. DOI: 10.1016/S0022-1139(00)83113-9.
  17. ↑ Cox, J. D.; Wagman, D. D.; Medvedev, V. A. CODATA Key Values for Thermodynamics; Hemisphere: New York, 1989. ISBN 0891167587, <http://www.codata.org/resources/databases/key1.html>.

Further reading

External links

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