Ion configuration in the crystal structure of tetraethylammonium difluorophosphate ([TEA][PO2F2]) is highly related to that in tetraethylammonium tetrafluoroborate ([TEA][BF4]). Both [TEA][PO2F2] and [TEA][BF4] exhibit a crystal-plastic crystal phase transition above room temperature (323 and 340 K, respectively), and the plastic crystal phase has a NaCl-type structure. The TEA(+) cation in both the salts adopts a trans-gauche conformer in the crystal structure, whereas the trans-trans conformer is dominant in the plastic crystal structure.