Acidic Salts of the Decaoxodiperiodic Acid: NiH4I2O10· 6H2O, ZnH4I2O10· 6H2O andMgH4I2O10· 6H2O; Crystal Structures, Vibrational Spectra and Thermal Decomposition

By crystallization from strongly acidic aqueous solutions, nickel and zinc tetrahydrogen-decaoxodiperiodate hexahydrate, NiH4I2O10·6H2O and ZnH4I2O10·6H2O, have been obtained and found to be isotypic to CuH4I2O10·6H2O (P21/c, no. 14) with the lattice parameters a = 1070.3, b = 544.0, c = 1187.2 pm, β = 112.6° for the Ni compound and a = 1073.3, b = 545.3, c = 1189.5 pm and β = 112.5° for the Zn compound. The crystal structure of MgH4I2O10·6H2O has been reinvestigated and contrary to former results found to be isotypic to the Cu compound as well. IR and Raman spectra are given and analyzed with respect to the internal vibrations of the H4I2O10 2− ion and the hydrogen bonding system. According to high-temperature Raman spectra and DTA and TG measurements, the compounds decompose in the temperature range up to 300 °C via unknown salts with the anions H4IO6 2− and IO4 − to the corresponding iodates. In the case of the Ni compound the exothermic decomposition to the iodate occurs in two steps.