Chlorotrifluorosilane Explained

Chlorotrifluorosilane is an inorganic gaseous compound with formula SiClF₃ composed of silicon, fluorine and chlorine. It is a silane that substitutes hydrogen with fluorine and chlorine atoms.

Production

By heating a mixture of anhydrous aluminium chloride and sodium hexafluorosilicate to between 190 and 250 °C a mixture of gases containing chlorotrifluorosilane is given off. These are condensed at -196 °C degrees and fractionally distilled at temperatures up to -78 °C.^[1]

SiClF₃ can be made by reacting silicon tetrachloride and silicon tetrafluoride gases at 600 °C, producing a mixture of fluorochlorosilanes including about one quarter SiClF₃.^[2]

SiClF₃ can be made by reacting silicon tetrachloride with antimony trifluoride. An antimony pentachloride catalyst assists. The products are distilled to separate it out from tetrafluorosilane and dichlorodifluorosilane.^{[3] [4]}

At high temperatures above 500 °C silicon tetrafluoride can react with phosphorus trichloride to yield some SiClF₃. This is unusual because SiF₄ is very stable.^[5]

Silicon tetrachloride can react with trifluoro(trichloromethyl)silane to yield SiClF₃ and CCl₃SiCl₃.^[6]

2-Chloroethyltrifluorosilane or 1,2-dichloroethyltrifluorosilane can be disassociated by an infrared laser to yield SiClF₃ and C₂H₄ (ethylene) or vinyl chloride. By tuning the laser to a vibration frequency of a particular isotope of silicon, different isotopomers can be selectively broken up in order to have a product that only concentrates one isotope of silicon. So silicon-30 can be increased to 80% by using the 934.5 cm⁻¹ line in a CO₂ laser.^[7]

The first published preparation of SiClF₃ by Schumb and Gamble was by exploding hexafluorodisilane in chlorine: Si₂F₆ + Cl₂ → 2SiClF₃. Other products of this explosion may include amorphous silicon, SiCl₂F₂ and SiF₄.^[8]

Chlorine reacts with silicon tetrafluoride in the presence of aluminium chips at 500-600 °C to make mostly silicon tetra chloride and some SiClF₃.^[9]

Mercuric chloride when heated with SiF₃Co(CO)₄ breaks the bond to form a 90% yield of SiClF₃.^[10]

The combination of SiF₄ and chlorodimethylphosphine yields some SiClF₃.^[11]

Trifluorosilane SiHF₃ reacts with gaseous chlorine to yield SiClF₃ and HCl.^[12]

Properties

Molecular size and angles

Bond length for Si–Cl is 1.996 Å and for Si–F is 1.558 Å. The bond angle ∠FSiCl = 110.2° and ∠FSiF = 108.7°.^[13] The bond length between silicon and chlorine is unusually short, indicating a 31% double bond. This can be explained by the more ionic fluoride bonds withdrawing some charge allowing a partial positive charge on the chlorine.^[14]

The molecular dipole moment is 0.636 Debye.^[13]

Bulk properties

Between 129.18 and 308.83 K the vapour pressure in mm Hg at temperature T in K is given by log₁₀ P = 102.6712 -2541.6/T -43.347 log₁₀ T + 0.071921T -0.000045231 T².^[15]

The heat of formation of chlorotrifluorosilane is -315.0 kcal/mol at 298K.^[16]

Reactions

Chlorotrifluorosilane is hydrolysed by water to produce silica.

Chlorotrifluorosilane reacts with trimethylstannane ((CH₃)₃SnH) at room temperature to make trifluorosilane in about 60 hours.^[17]

Use

Proposed uses include a dielectric gas with a high breakdown voltage, and low global warming potential, a precursor for making fluorinated silica soot, and a vapour deposition gas.

Related substances

Chlorotrifluorosilane can form an addition compound with pyridine with formula SiClF₃.2py (py=pyridine)^[18] An addition compound with trimethylamine exists.^{[19] [20]} This addition compound is made by mixing trimethylamine vapour with Chlorotrifluorosilane and condensing out a solid at -78 °C. If this was allowed to soak in trimethylamine liquid for over eight hours, a diamine complex formed (2Me₃N·SiClF₃).^[20] At 0° the disassociation pressure of the monoamine complex was 23 mm Hg.^[20]

SiClF₃⁻ is a trigonal bipyramidal shape with a Cl and F atom on the axis. It is formed when gamma rays hit the neutral molecule.^[21]

Chlorotetrafluorosilicate (IV) (SiClF₄⁻) can form a stable a pale yellow crystalline compound tetraethylammonium chlorotetrafluorosilicate.^[22]

Extra reading

• Wodarczyk. F.J. Wilson. E.B. Radio frequency-microwave double resonance as a tool in the analysis of microwave spectra. Journal of Molecular Spectroscopy. March 1971. 37. 3. 445–463. 10.1016/0022-2852(71)90176-7. 1971JMoSp..37..445W.
• Sheridan. John. Gordy. Walter. Microwave Spectra and Molecular Constants of Trifluorosilane Derivatives. SiF3H, SiF3CH3, SiF3Cl, and SiF3Br. Physical Review. March 1950. 77. 5. 719. 10.1103/PhysRev.77.719. 1950PhRv...77..719S.
• Sheridan. John. Gordy. Walter. The Microwave Spectra and Molecular Structures of Trifluorosilane Derivatives. The Journal of Chemical Physics. 1951. 19. 7. 965. 10.1063/1.1748418. 1951JChPh..19..965S.
• Ault. Bruce S.. Infrared matrix isolation studies of the M+SiF5- ion pair and its chlorine-fluorine analogs. Inorganic Chemistry. December 1979. 18. 12. 3339–3343. 10.1021/ic50202a012.
• Stanton. C. T.. McKenzie. S. M.. Sardella. D. J.. Levy. R. G.. Davidovits. Paul. Boron atom reactions with silicon and germanium tetrahalides. The Journal of Physical Chemistry. August 1988. 92. 16. 4658–4662. 10.1021/j100327a020.

Notes and References

1. Schmeißer und Herber t Jenkne r. Martin. Jenkner. Herbert. Zurr Kenntnis anorganischer Säurefluoride (i) Über Reaktione n des Siliciumtetrafluorids (bzw. des Natriumsilicofluorids). Verlag Zeitschrift für Naturforschung. 1952. 191–192. 10.1515/znb-1952-0310. 95929863.
2. US. 2395826. Preparation of chlorofluorosilanes. 3 May 1946. Hill, Julian W. . Lindsey Jr. V, Richard .
3. Booth. Harold Simmons. Swinehart. Carl F.. The Fluorochlorosilanes. Journal of the American Chemical Society. July 1935. 57. 7. 1333–1337. 10.1021/ja01310a050.
4. Book: 151. Annual Reports on the Progress of Chemistry. 1940.
5. Suresh. B.S.. Padma. D.K.. Halogen exchange reactions of silicon tetrafluoride with phosphorus trichloride and phosphoryl chloride. Journal of Fluorine Chemistry. September 1985. 29. 4. 463–466. 10.1016/S0022-1139(00)85111-8. 1985JFluC..29..463S .
6. Weidenbruch. Manfred. Pierrard. Claude. Reaktionen von Halogeniden des Siliciums, Germaniums und Zinns mit Diazomethan und Dichlorcarben- Transfer-Agentien. Chemische Berichte. April 1977. 110. 4. 1545–1554. 10.1002/cber.19771100437. de.
7. Dementyev. Petr S.. Nizovtsev. Anton S.. Chesnokov. Evgenii N.. Infrared photoreaction of 2-chloroethyltrifluorosilane. Journal of Photochemistry and Photobiology A: Chemistry. July 2011. 222. 1. 77–80. 10.1016/j.jphotochem.2011.05.004. 2011JPPA..222...77D .
8. Schumb. Walter C.. Gamble. E. Lee. Fluorochlorides of Silicon. Journal of the American Chemical Society. October 1932. 54. 10. 3943–3949. 10.1021/ja01349a018.
9. Book: Inorganic Reactions and Methods, the Formation of Bonds to Halogens. 361. 9780470145388. Zuckerman. J. J. 2009-09-17. John Wiley & Sons .
10. Book: Organosilicon Chemistry: 2: Plenary Lectures Presented at the Second International Symposium on Organosilicon Chemistry. 443. 9781483284828. 2013-09-03. Zhou. Yong. Elsevier .
11. Book: 450. Journal of the Chinese Chemical Society. 1999. Chinese Chemical Society . 9780021926541.
12. Book: 103. Silicon: Supplement volume. 9783540937289. Gmelin. Leopold. 1996.
13. Cox. A.P.. Gayton. T.R.. Rego. C.A.. Microwave spectrum, structure, quadrupole coupling constant and dipole moment of chlorotrifluorosilane and iodotrifluorosilane. Journal of Molecular Structure. November 1988. 190. 419–434. 10.1016/0022-2860(88)80301-6. 1988JMoSt.190..419C.
14. Book: 312. The Nature of the Chemical Bond and the Structure of Molecules and Crystals: An Introduction to Modern Structural Chemistry. registration. Cornell University Press. 0801403332. Pauling. Linus. January 1960.
15. Book: Yaws. Carl L.. Nijhawan. Sachin. Bu. Li. Handbook of Vapor Pressure. 1995. 4. 352–357. 10.1016/S1874-8813(06)80008-9. Appendix C Coefficients for vapor pressure equation. 9780884153948.
16. Gordon. M. S.. Francisco. J. S.. Schlegel. H. B.. THEORETICAL INVESTIGATIONS OF THE THERMOCHEMISTRY AND THERMAL DECOMPOSITION OF SILANES, HALOSILANES, AND ALKYLSILANES. Advances in Silicon Chemistry. 1993. 2. 153. JAI Press.
17. Book: 83. Silicon: Supplement volume. 9783540937289. Gmelin. Leopold. 1996. Springer .
18. Hensen. Karl. Wagner. Hans Bernhard. Über einige Verbindungen gemischter Siliciumhalogenide mit Pyridin. Chemische Berichte. February 1976. 109. 2. 411–414. 10.1002/cber.19761090201. de.
19. Book: 19–20. Stereochemistry, mechanism and silicon: An introduction to the dynamic stereochemistry and reaction mechanisms of silicon centers. registration. McGraw-Hill. Sommer. Leo Harry. 1965.
20. Fergusson. J. E.. Grant. D. K.. Hickford. R. H.. Wilkins. C. J.. 21. Co-ordination of trimethylamine by halides of silicon, germanium, and tin. Journal of the Chemical Society (Resumed). 1959. 99–103. 10.1039/JR9590000099.
21. Hasegawa. Akinori. Uchimura. Schunichiro. Koseki. Kohji. Hayashi. Michiro. ESR spectrum and structure of the SiF3Cl− radical anion. Chemical Physics Letters. January 1978. 53. 2. 337–340. 10.1016/0009-2614(78)85410-4. 1978CPL....53..337H.
22. Edwards. H.G.M.. Fawcett. V.. Rose. S.J.. Smith. D.N.. The preparation and Raman spectroscopic study of the chlorotetrafluorosilicate (IV) ion, SiF4Cl−. Journal of Molecular Structure. May 1992. 268. 4. 353–361. 10.1016/0022-2860(92)80222-4. 1992JMoSt.268..353E.