RAMAN-SPECTRA OF SOME HEXA-AQUO METAL(II) HEXAFLUOROSILICATE(IV) (M(H2O)6SIF6) SALTS BETWEEN 10-K AND 300-K

Raman spectra of Ni(H2O)6SiF6, Ni((D2O)6SiF6 and Fe(H2O)6SiF6 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 R3 symmetry at all temperatures, but below ∼ 230 K the lattice band spectra of the ferrous salt cannot be fitted to R3m or R3, which is consistent with the recent findings that there is a phase transition at about 250 K with the low temperature space group being P21/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(H2O)6SiF6 at 300 K is also given for comparison. Copyright © 1979 Heyden & Son Ltd.