Phosphorus pentafluoride

Phosphorus pentafluoride
Names
	IUPAC name Phosphorus pentafluoride
	Other names Phosphorus(V) fluoride; Pentafluoridophosphorus; Pentafluorophosphorane
Identifiers
CAS Number	7647-19-0 ;
3D model (JSmol)	Interactive image;
ChemSpider	22715 ;
ECHA InfoCard	100.028.730
EC Number	231-602-3;
PubChem CID	24295;
RTECS number	TH4070000;
UNII	0OU1ESO71L ;
UN number	2198
CompTox Dashboard (EPA)	DTXSID9064760 ;
	InChI InChI=1S/F5P/c1-6(2,3,4)5 Key: OBCUTHMOOONNBS-UHFFFAOYSA-N ; InChI=1/F5P/c1-6(2,3,4)5 Key: OBCUTHMOOONNBS-UHFFFAOYAH;
	SMILES FP(F)(F)(F)F;
Properties
Chemical formula	PF5
Molar mass	125.966 g/mol
Appearance	colourless gas
Odor	unpleasant
Density	5.527 kg/m3 (g/L)
Melting point	−93.78 °C (−136.80 °F; 179.37 K)
Boiling point	−84.6 °C (−120.3 °F; 188.6 K)
Solubility in water	hydrolysis
Structure
Molecular shape	trigonal bipyramidal
Dipole moment	0 D
Hazards
Flash point	Non-flammable
Related compounds
Other anions	Phosphorus pentachloride; Phosphorus pentabromide; Phosphorus pentaiodide
Other cations	Arsenic pentafluoride; Antimony pentafluoride; Bismuth pentafluoride
Related compounds	Phosphorus trifluoride
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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	Infobox references

Phosphorus pentafluoride, P F₅, is a phosphorus halide. It is a colourless, toxic gas that fumes in air.[1][2]

Preparation

Phosphorus pentafluoride was first prepared in 1876 by the fluorination of phosphorus pentachloride using arsenic trifluoride, which remains a favored method:[1]

3 PCl₅ + 5 AsF₃ → 3 PF₅ + 5 AsCl₃

Structure

Single-crystal X-ray studies indicate that the PF₅ has trigonal bipyramidal geometry. Thus it has two distinct types of P−F bonds (axial and equatorial): the length of an axial P−F bond is distinct from the equatorial P−F bond in the solid phase, but not the liquid or gas phases due to Pseudo Berry Rotation.

Fluorine-19 NMR spectroscopy, even at temperatures as low as −100 °C, fails to distinguish the axial from the equatorial fluorine environments. The apparent equivalency arises from the low barrier for pseudorotation via the Berry mechanism, by which the axial and equatorial fluorine atoms rapidly exchange positions. The apparent equivalency of the F centers in PF₅ was first noted by Gutowsky.[3] The explanation was first described by R. Stephen Berry, after whom the Berry mechanism is named. Berry pseudorotation influences the ¹⁹F NMR spectrum of PF₅ since NMR spectroscopy operates on a millisecond timescale. Electron diffraction and X-ray crystallography do not detect this effect as the solid state structures are, relative to a molecule in solution, static and can not undergo the necessary changes in atomic position.

Lewis acidity

Phosphorus pentafluoride is a Lewis acid. This property is relevant to its ready hydrolysis. A well studied adduct is PF₅(pyridine). With primary and secondary amines, the adducts convert readily to dimeric amido-bridged derivatives with the formula [PF₄(NR₂)]₂. A variety of complexes are known with bidentate ligands.[4]

Hexafluorophosphoric acid (HPF₆) is derived from phosphorus pentafluoride and hydrogen fluoride. Its conjugate base, hexafluorophosphate (PF₆^–), is a useful non-coordinating anion.

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References

Kwasnik, W. (1963). "Phosphorus(V) fluoride". In Brauer, G. (ed.). Handbook of Preparative Inorganic Chemistry. 1 (2nd ed.). New York: Academic Press. p. 190.
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
Gutowsky, H. S.; McCall, D. W.; Slichter, C. P. (1953). "Nuclear Magnetic Resonance Multiplets in Liquids". J. Chem. Phys. 21 (2): 279. doi:10.1063/1.1698874.
Wong, Chih Y.; Kennepohl, Dietmar K.; Cavell, Ronald G. (1996). "Neutral Six-Coordinate Phosphorus". Chemical Reviews. 96: 1917-1952. doi:10.1021/cr9410880. PMID 11848816.

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[Brauer-1] Kwasnik, W. (1963). "Phosphorus(V) fluoride". In Brauer, G. (ed.). Handbook of Preparative Inorganic Chemistry. 1 (2nd ed.). New York: Academic Press. p. 190.

[2] Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.

[3] Gutowsky, H. S.; McCall, D. W.; Slichter, C. P. (1953). "Nuclear Magnetic Resonance Multiplets in Liquids". J. Chem. Phys. 21 (2): 279. doi:10.1063/1.1698874.

[4] Wong, Chih Y.; Kennepohl, Dietmar K.; Cavell, Ronald G. (1996). "Neutral Six-Coordinate Phosphorus". Chemical Reviews. 96: 1917-1952. doi:10.1021/cr9410880. PMID 11848816.