Phosphorus pentafluoride

Chembox new
Name = Phosphorus pentafluoride
ImageFile = Phosphorus-pentafluoride-2D-dimensions.png ImageName = Structure of the phosphorus pentafluoride molecule
ImageFile1 = Phosphorus-pentafluoride-3D-vdW.png ImageName1 = Space-filling model of the phosphorus pentafluoride molecule
IUPACName = phosphorus pentafluoride
OtherNames = phosphorus(V) fluoride
pentafluorophosphorus(V)
Section1 = Chembox Identifiers
CASNo = 7647-19-0
RTECS =
Section2 = Chembox Properties
Formula = phosphorusfluorine|5
MolarMass = 125.9685 g mol⁻¹
Appearance = colourless gas
Density =
Solubility = decomposes
MeltingPt = −93.78 °C (179.4 K)
BoilingPt = −84.5 °C (188.7 K)
Section3 = Chembox Structure
MolShape = trigonal bipyramidal
CrystalStruct = e.g. triclinic, monoclinic, orthorhombic, hexagonal, trigonal, tetragonal, cubic, and mention "close packed" or similar. You may also cite what class it belongs to, e.g. CdCl₂
Dipole = 0 D
Section7 = Chembox Hazards
ExternalMSDS =
MainHazards =
RPhrases =
SPhrases =
Section8 = Chembox Related
Function = phosphorus halides
OtherFunctn = PF₃
PCl₅
sulfur tetrafluoride
Function = pentafluorides
OtherFunctn = SbF₅, ClF₅, BrF₅, IF₅, TaF₅, UF₅
OtherCpds = VOF₃

Phosphorus pentafluoride, PF₅, is a phosphorus halide. The phosphous atom is in the highest oxidation state possible, +5. PF₅ is a highly reactive compound, existing as a colourless gas at room temperature and pressure.

tructure

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.

¹⁹F 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. [Gutowsky, H. S.; McCall, D. W.; Slichter, C. P. "Nuclear Magnetic Resonance Multiplets in Liquids" Journal of Chemical Physics 1953, volume 21, 279.] . The explanation was first described by R. Stephen Berry, after whom the Berry mechanism is named. Berry pseudorotation influences the¹⁹F 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

*

External links

* [http://www.chemsoc.org/ExemplarChem/entries/2003/durham_shah/trig_bipyram.htm/ PF5]