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Phosphorus pentafluoride

Names
IUPAC name Phosphorus pentafluoride
Other names Phosphorus(V) fluoride Pentafluoridophosphorus Pentafluorophosphorane
Identifiers
CAS Number	7647-19-0
ECHA InfoCard	100.028.730
PubChem CID	24295
RTECS number	TH4070000
CompTox Dashboard (EPA)	DTXSID9064760
Properties
Chemical formula	PF5
Molar mass	125.96577 g/mol
Appearance	colourless gas
Density	5.527 g/cm
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
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is  ?) Infobox references

Phosphorus pentafluoride, PF₅, is a phosphorus halide. It's a colourless gas at room temperature and pressure.

Structure

Single-crystal X-ray studies indicate PF₅ molecule has two distinct P−F bonds (axial and equatorial): P−F_ax = 158.0 pm and P−F_eq = 152.2 pm. Gas-phase electron diffraction analysis gives similar values: P−F_ax = 158 pm and P−F_eq = 153 pm.

Fluorine-19 NMR spectroscopy, 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. The explanation was first described by R. Stephen Berry, after whom the Berry mechanism is named. Berry pseudorotation influences the F NMR spectrum of PF₅ since NMR spectroscopy operates on a millisecond timescale. Electron diffraction and X-ray crystallography do not detect this effect as their timescales are significantly shorter than for NMR spectroscopy.

References

1. Gutowsky, H. S.; McCall, D. W.; Slichter, C. P. (1953). "Nuclear Magnetic Resonance Multiplets in Liquids". J. Chem. Phys. 21: 279. doi:10.1063/1.1698874.{{cite journal}}: CS1 maint: multiple names: authors list (link)

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

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