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Template:Chembox new 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.

F 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 theF 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

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1. Gutowsky, H. S.; McCall, D. W.; Slichter, C. P. "Nuclear Magnetic Resonance Multiplets in Liquids" Journal of Chemical Physics 1953, volume 21, 279.

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

External links

• PF5

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