# How many fluorine environments exist in PF_5? Are the fluorines equivalent?

Of course, there is a catch. Let us consider typical 5-coordinate compound, $P C {l}_{5}$, and $P {F}_{5}$ are suitable, and have to a first approx. trigonal bipyramidal ${D}_{3 h}$ symmetry. $P {F}_{5}$ is especially suitable given that both atoms are 100% $I = \frac{1}{2}$, and ""^19F{""^1H}, and ""^31P{""^1H} $\text{NMR spectroscopies}$ are VERY convenient means to monitor their solution behaviour.
For $P {F}_{5}$ there are CLEARLY 2 fluorine environments, axial and equatorial. Under normal conditions, however, only one $F$ environment is observed in the spectrum (as a doublet due to ${\text{^31P,}}^{19} F$ coupling). There exists a fairly soft mechanism of intramolecular exchange thru so-called $\text{pseudorotation}$ or $\text{turnstile rotation}$, which exchanges the axial ligands for equatorial ligands and vice versa. At lower temperatures, this exchange can be frozen out, and the two enviroments observed in the solution spectrum.