LATTICE VIBRATION-SPECTRA .82. BRUCITE-TYPE HYDROXIDES M(OH)(2) (M=CA, MN, CO, FE, CD) - IR AND RAMAN-SPECTRA, NEUTRON-DIFFRACTION OF FE(OH)(2)

Fe3+-free white rust Fe(O(H,D))(2) has been prepared and characterized by X-ray, neutron diffraction, and IR and Raman spectroscopic methods. The crystal structure of Fe(OH)2 (space group P ($) over bar 3ml, Z = 1, a = 326.289(1) pm and c = 460.4(1)pm; V = 42.45(1) x 10(6) pm(3)) was refined to a final RI = 5.6%. The results of IR and Raman spectra of the brucite-type M(O(H,D))(2) (M = Ca, Mn, Fe, Co, Cd) are presented and discussed in terms of (i) assignment of the librational and translational modes, (ii) frequency shifts with respect to M-O bond lengths, unit-cell volumes and masses of the atoms involved, and (iii) the nature of the large unit-cell group splittings of the OH stretching modes. Due to different bonding, i.e. more or less covalent, the brucite-type hydroxides can be divided into two groups of M = Ca, Mg, and M = Fe, Co, Ni, and Cd, respectively.