The hydrolysis and methanolysis of N(CH3)(4)PF4 were studied by multinuclear NMR and vibrational spectroscopy. With an equimolar amount of water in CH3CN solution, PF4- forms HPO2F- and HPF5- in a 1:1 mole ratio. With an excess of water, HPO2F- is the sole product which was also obtained by the hydrolysis of HPF5-. In the presence of a large excess of F-, the hydrolysis of PF4- With an equimolar amount of water produces POF2-. The resulting N(CH3)(4)POF2 is the first known example of a stable POF2- salt. The geometries and vibrational spectra of POF2- and HPO2F- were calculated by ab initio methods, and normal coordinate analyses were carried out for POF2-, HPO2F-, and the isoelectronic SOF2, HSO2F, and ClOF2+ species. The F- affinities of FPO, HPO2, and related species and the reaction enthalpies of the hydrolysis reactions of the PF4- and HPF5- anions were also calculated by ab initio methods and are in accord with the experimental data. The methanolysis of PF4- produces PF2(OCH3) and PF(OCH3)(2) as the main products.