The elusive POF4 - anion has been characterized for the first time. It is formed from N(CH3)4F and POF3 in CHF3 solution at −140 °C and can be observed at this temperature by 19F and 31P NMR spectroscopy. Between −140 and −100 °C it reacts with POF3 forming the OF2P−O−PF5 - anion, which, at higher temperatures, reacts with F- anions to give PO2F2 - and PF6 -. This reaction sequence provides a low activation energy barrier pathway for the highly exothermic dismutation of pseudo-trigonal-bipyramidal POF4 - to tetrahedral PO2F2 - and octahedral PF6 - and explains the previous failures to isolate POF4 - salts. In addition to POF4 -, OF2POPF5 -, and PO2F2 -, the protonated form of OF2POPF5 -, i.e., HOF2POPF5, was also identified as a byproduct by NMR spectroscopy. The structure, vibrational spectra, force field, NMR parameters, and dismutation energy of POF4 - were calculated by ab initio electronic structure methods using, where required, the closely related and well-known PF4 - ion and POF3, PF3, SOF4, and SF4 molecules for the determination of scaling factors. Although the structures and dismutation energies of isoelectronic POF4 - and SOF4 are very similar, their dismutation behavior is strikingly different. While POF4 - dismutates rapidly at low temperatures, SOF4 is kinetically stable toward dismutation to SO2F2 and SF6. This fact is attributed to the lack of a low activation energy barrier pathway for SOF4. Furthermore, the dismutation energy calculations for POF4 -, SOF4, and ClOF3 revealed very large errors in the previously published thermodynamic data for the heats of formations of SO2F2 and SOF4 and the dismutation reaction energy of POF4 -. Energy barriers and the C 4 v transition states for the Berry-style pseudorotational exchange of equatorial and axial fluorines in POF4 -, SOF4, PF4 -, and SF4 were also calculated and can account for the observation that on the NMR time scale the exchange in PF4 - and SF4 can be frozen out at about −40 °C, while in POF4 - and SOF4 it is still rapid at −140 and −150 °C, respectively.