The Raman spectra of some hexa‐aquo metal(II) hexafluorosilicate(IV) (M(H) 2 O) 6 SiF 6 ) salts between 10 K and 300 K

Raman spectra of Ni(H 2 O) 6 SiF 6 , Ni((D 2 O) 6 SiF 6 and Fe(H 2 O) 6 SiF 6 have been observed between room temperatures and 10 K, and the measured lines assigned to the various modes of vibration. The spectra of the nickel salts are consistent with R 3 symmetry at all temperatures, but below ∼ 230 K the lattice band spectra of the ferrous salt cannot be fitted to R 3 m or R 3 , which is consistent with the recent findings that there is a phase transition at about 250 K with the low temperature space group being P 2 1 / c . The weakness of the water vibrational bands at room temperature is interpreted in terms of the barrier to 180° flip motion of the water molecules and the coupling of 180° flipping with the water vibrations. The Raman spectrum of polycrystalline Mg(H 2 O) 6 SiF 6 at 300 K is also given for comparison.