SYNTHESIS, SPECTROSCOPIC AND STRUCTURAL STUDIES OF ALKALI-METAL NICKEL PERIODATES MNIIO6 (M=NA, K, RB, CS OR NH4)

The dark red-purple nickel(IV) periodates MNiIO6 (M = Na, K, Rb, Cs or NH4) have been prepared by peroxohexaoxodisulfate oxidation of mixtures of nickel(II) salts, MNO3 and periodate ions in hot aqueous solution. Powder X-ray diffraction studies showed that the structures adopted the space group P312, with hexagonal close-packed layers of oxide ions. One-third of the octahedral holes in every second layer contained M ions, and in the other layers one-third of the octahedral holes contained I and one-third Ni. The Ni-O, I-O, Ni ... I and Ni ... Ni distances have been determined by a combination of nickel and iodine K-edge extended X-ray absorption fine structure (EXAFS) data. IR, Raman and UV/VIS spectroscopic data for MNiIO6 were obtained. Iodine K-edge EXAFS data have also been obtained for the related periodates M'M''IO6 (M' = K or Rb; M'' = Ge, Sn, Pb or Mn).