Abstract Indications are that CsPF 6(I) at ambient conditions is cubic with a possible space group of Fm3 m-O 5 h . A slight distortion of the unit cell cannot, however, be ruled out. Assuming Fm3 m symmetry the Raman spectra of CsPF 6(I) are consistent with a disordered model in which the PF − 6 ions are tilted away from the crystallographic axes. The phase transition which occurs below 90 K in CsPF 6 is reflected in the vibrational spectra and further significant changes occur below 60 K particularly in the Raman bands. It is not yet clear whether these changes represent the establishment of long-range order or whether a further phase of CsPF 6 exists below 60 K. A possible structure for CsPF 6 at very low temperatures is discussed.