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Krypton difluoride

Krypton difluoride


IUPAC name	krypton(II) fluoride
Other names	krypton difluoride, krypton fluoride
Identifiers
CAS number	13773-81-4
Properties
Molecular formula	KrF₂
Molar mass	121.7968 g mol⁻¹
Appearance	colourless solid^[1]
Density	3.24 g/cm³, solid^[1]
Structure
Crystal structure	Body Centred Tetragonal
Molecular shape	linear
Dipole moment	0 D
Related Compounds
Related compounds	Kr(OTeF₅)₂; XeF₂
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Krypton difluoride, KrF₂, was the first compound of krypton discovered.^[2] It is a volatile, colourless solid. The structure of the KrF₂ molecule is linear, with Kr−F distances of 188.9 pm. It reacts with strong Lewis acids to form salts of the KrF⁺ and Kr₂F₃⁺ cations.^[3]

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Synthesis

Krypton difluoride can be synthesized using many different methods including electrical discharge, photochemical, irradiation, hot wire and proton bombardment.

Electrical discharge

The first method used to make krypton difluoride and the only one ever reported to produce krypton tetrafluoride was the electrical discharge method.^[4] The electrical discharge method involves having 1:1 to 2:1 mixtures of F₂ to Kr at a pressure of 40 to 60 torr and then arcing large amounts of energy between it.^[5] Rates of almost 0.25g/h can be achieved.^[6] The problem with this method is that it is unreliable with respect to yield.

Proton Bombardment

Using proton bombardment for the production of KrF₂ has a maximum production rate of about 1g/h.^[7] This is achieved by bombarding mixtures of Kr and F₂ with a proton beam that is operating at an energy level of 10MeV and at a temperature of about 133K.^[8] It is a fast method of producing relatively large amounts of KrF₂, it runs into difficulties in that it requires a source of α-particles which usually would come from a cyclotron.^[9]

Photochemical

The photochemical process for the production of KrF₂ involves the use of UV light and can produce under ideal circumstances 1.22g/h.^[10] The ideal wavelengths to use are in the range of 303-313nm.^[11] It is important to note that harder UV radiation is detrimental to the production of KrF₂.^[12] In order to avoid the harder wavelengths, simply using Pyrex glass or Vycor or quartz will significantly increase yield because they all block harder UV light.^[13] In a series of experiments performed by S. A Kinkead et. al, is was shown that a quartz insert (UV cut off of 170nm) produced on average 158mg/h, Vycor 7913 (UV cut off of 210nm) produced on average 204mg/h and Pyrex 7740 (UV cut off of 280nm) produced on average 507mg/h.^[14] It is clear from these results that higher energy ultra violet light reduces the yield significantly. The ideal circumstances for the production KrF₂ by a photochemical process appear to occur when Kr is a solid and Fluorine is a liquid which occur at 77K.^[15] The biggest problem with this method is that is requires the handling of liquid F₂ and the potential of it being released if it becomes over pressurized.^[16]

Hot Wire

The hot wire method for the production of KrF₂ involves having the krypton in a solid state with a hot wire running a few centimeters away from it as fluorine gas is then run past the wire.^[17] The wire has a large current, causing it to reach temperatures around 680C.^[18] This causes the fluorine gas to split into its radicals which then can react with the solid krypton.^[19] Under ideal conditions, it has been known to reach a maximum yield of 6g/h.^[20] In order to achieve optimal yields the gap between the wire and the solid krypton should be 1cm, giving rise to a temperature gradient of about 900C/cm.^[21] The only major downside to this method is the amount of electricity that has to be passed through the wire thus making it dangerous if not properly set up.^[22]

Cystallographic Morphologies

Krypton difluoride can exist in one of two possible cystallographic morphologies: α-phase and β-phase. β-KrF₂ generally exists at above -80C, while the α- KrF₂ is more stable at lower temperatures.^[23] The unit cell of α-KrF₂ is body centred tetragonal.

Related compounds

xenon difluoride, XeF₂

References

^ ^a ^b pp. 442–443, Handbook of Inorganic Chemicals, Pradyot Patnaik, McGraw-Hill Professional, 2003. ISBN 0070494398.
^ Grosse, A. V.; Kirschenbaum, A. D.; Streng, A. G.; Streng, L. V. "Krypton Tetrafluoride: Preparation and Some Properties" Science, 1963, volume 139, pages 1047-1048. doi:10.1126/science.139.3559.1047.
^ Lehmann, J. F.; Dixon, D. A.; Schrobilgen, G. J. "X-ray Crystal Structures of α-KrF₂, [KrF][MF₆] (M = As, Sb, Bi), [Kr₂F₃][SbF₆]^.KrF₂, [Kr₂F₃]₂[SbF₆]₂^.KrF₂, and [Kr₂F₃][AsF₆]^.[KrF][AsF₆]; Synthesis and Characterization of [Kr₂F₃][PF₆]^.nKrF₂; and Theoretical Studies of KrF₂, KrF⁺, Kr₂F₃⁺, and the [KrF][MF₆] (M = P, As, Sb, Bi) Ion Pairs” Inorganic Chemistry 2001, volume 40, pages 3002-3017. doi:10.1021/ic001167w
^ Lehmann, John. F.; Mercier, Hélène P.A.; Schrobilgen, Gary J. The chemistry of Krypton. Coordination Chemistry Reviews. 2002, 233-234, 1-39
^ Lehmann, John. F.; Mercier, Hélène P.A.; Schrobilgen, Gary J. The chemistry of Krypton. Coordination Chemistry Reviews. 2002, 233-234, 1-39
^ Kinkead, S. A.; Fitzpatrick, J. R.; Foropoulos, J. Jr.; Kissane, R. J.; Purson, D. Photochemical and thermal Dissociation Synthesis of Krypton Difluoride. Inorganic Fluorine Chemistry: Toward the 21st Century, Thrasher, Joseph S.; Strauss, Steven H.: American Chemical Society. San Francisco, California, 1994. 40-54.
^ Lehmann, John. F.; Mercier, Hélène P.A.; Schrobilgen, Gary J. The chemistry of Krypton. Coordination Chemistry Reviews. 2002, 233-234, 1-39
^ Lehmann, John. F.; Mercier, Hélène P.A.; Schrobilgen, Gary J. The chemistry of Krypton. Coordination Chemistry Reviews. 2002, 233-234, 1-39
^ Lehmann, John. F.; Mercier, Hélène P.A.; Schrobilgen, Gary J. The chemistry of Krypton. Coordination Chemistry Reviews. 2002, 233-234, 1-39
^ Lehmann, John. F.; Mercier, Hélène P.A.; Schrobilgen, Gary J. The chemistry of Krypton. Coordination Chemistry Reviews. 2002, 233-234, 1-39
^ Lehmann, John. F.; Mercier, Hélène P.A.; Schrobilgen, Gary J. The chemistry of Krypton. Coordination Chemistry Reviews. 2002, 233-234, 1-39
^ Kinkead, S. A.; Fitzpatrick, J. R.; Foropoulos, J. Jr.; Kissane, R. J.; Purson, D. Photochemical and thermal Dissociation Synthesis of Krypton Difluoride. Inorganic Fluorine Chemistry: Toward the 21st Century, Thrasher, Joseph S.; Strauss, Steven H.: American Chemical Society. San Francisco, California, 1994. 40-54.
^ Kinkead, S. A.; Fitzpatrick, J. R.; Foropoulos, J. Jr.; Kissane, R. J.; Purson, D. Photochemical and thermal Dissociation Synthesis of Krypton Difluoride. Inorganic Fluorine Chemistry: Toward the 21st Century, Thrasher, Joseph S.; Strauss, Steven H.: American Chemical Society. San Francisco, California, 1994. 40-54.
^ Kinkead, S. A.; Fitzpatrick, J. R.; Foropoulos, J. Jr.; Kissane, R. J.; Purson, D. Photochemical and thermal Dissociation Synthesis of Krypton Difluoride. Inorganic Fluorine Chemistry: Toward the 21st Century, Thrasher, Joseph S.; Strauss, Steven H.: American Chemical Society. San Francisco, California, 1994. 40-54.
^ Kinkead, S. A.; Fitzpatrick, J. R.; Foropoulos, J. Jr.; Kissane, R. J.; Purson, D. Photochemical and thermal Dissociation Synthesis of Krypton Difluoride. Inorganic Fluorine Chemistry: Toward the 21st Century, Thrasher, Joseph S.; Strauss, Steven H.: American Chemical Society. San Francisco, California, 1994. 40-54.
^ Lehmann, John. F.; Mercier, Hélène P.A.; Schrobilgen, Gary J. The chemistry of Krypton. Coordination Chemistry Reviews. 2002, 233-234, 1-39
^ Kinkead, S. A.; Fitzpatrick, J. R.; Foropoulos, J. Jr.; Kissane, R. J.; Purson, D. Photochemical and thermal Dissociation Synthesis of Krypton Difluoride. Inorganic Fluorine Chemistry: Toward the 21st Century, Thrasher, Joseph S.; Strauss, Steven H.: American Chemical Society. San Francisco, California, 1994. 40-54.
^ Lehmann, John. F.; Mercier, Hélène P.A.; Schrobilgen, Gary J. The chemistry of Krypton. Coordination Chemistry Reviews. 2002, 233-234, 1-39
^ Lehmann, John. F.; Mercier, Hélène P.A.; Schrobilgen, Gary J. The chemistry of Krypton. Coordination Chemistry Reviews. 2002, 233-234, 1-39
^ Kinkead, S. A.; Fitzpatrick, J. R.; Foropoulos, J. Jr.; Kissane, R. J.; Purson, D. Photochemical and thermal Dissociation Synthesis of Krypton Difluoride. Inorganic Fluorine Chemistry: Toward the 21st Century, Thrasher, Joseph S.; Strauss, Steven H.: American Chemical Society. San Francisco, California, 1994. 40-54.
^ Kinkead, S. A.; Fitzpatrick, J. R.; Foropoulos, J. Jr.; Kissane, R. J.; Purson, D. Photochemical and thermal Dissociation Synthesis of Krypton Difluoride. Inorganic Fluorine Chemistry: Toward the 21st Century, Thrasher, Joseph S.; Strauss, Steven H.: American Chemical Society. San Francisco, California, 1994. 40-54.
^ Lehmann, John. F.; Mercier, Hélène P.A.; Schrobilgen, Gary J. The chemistry of Krypton. Coordination Chemistry Reviews. 2002, 233-234, 1-39
^ Lehmann, John. F.; Mercier, Hélène P.A.; Schrobilgen, Gary J. The chemistry of Krypton. Coordination Chemistry Reviews. 2002, 233-234, 1-39

General reading

Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.

Categories: Fluorides | Krypton compounds

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Krypton_difluoride". A list of authors is available in Wikipedia.