Knowledge Bank

Although $PF3,PF5$ and $PF+6\mathrm{<mrow\; data-mjx-texclass="ORD">-</mrow>}$ are stable, well characterized species, as is the four coordinate $PF+6$ cation, the $PF4\mathrm{<mrow\; data-mjx-texclass="ORD">-</mrow>}$ anion has only recently been detected, and is relatively poorly characterized. It has bee observed in both mass spectrometry and ion cyclotron resonance, leading to a value for $\Delta Hf\mathrm{<mrow\; data-mjx-texclass="ORD">0</mrow>}=-335$ Kcal/mole and a fluoride ion affinity of $PF3$ of about 50 Kcal/mole. The $PF4\mathrm{<mrow\; data-mjx-texclass="ORD">-</mrow>}$ has now been synthesized by the salt/molecule matrix isolation technique. Reaction of CsF and $PF3$ in an argon matrix leads to the appearance of four bands, at 620, 711, 781 and $790cm-1$. These bands have been assigned to the four P-F stretching vibrations of the $PF4\mathrm{<mrow\; data-mjx-texclass="ORD">-</mrow>}$ anion in a $C2y$ structure analogous to SF. A study of the mixed chlorofluoro system gave similar results, but with a substantial decrease in yield as the number of chlorine atoms increased and fluorine atoms decreased.