Observation and study of new types of phase transitions in Co(ClO₄)₂.6H₂O and Ni(ClO₄)₂.6H₂O by EPR

Low-frequency vibrations and molecular motions of H2O molecules in [Ni(H2O)6](ClO4)2 and in [Ni(D2O)6](ClO4)2 studied with neutron scattering methods

“…This seems to be in correspondence with the conclusion from Ref. [10] referred to above that Phase III contains deformed water ligand octahedrons. We assign only those frequencies obtained at the lowest temperature of the measurement because for such a temperature they are resolved best.…”

“…Maybe no well-defined thermal history of the sample in Refs. [10,12] could be responsible for such disagreement or the structure changes are too small to be seen by Jain and Upreti [10] and Ghosh et al [12] whereas they are well seen by coherent scattering of neutrons on deuterated samples.…”

“…This is in disagreement with Refs. [10,12]. Maybe no well-defined thermal history of the sample in Refs.…”

“…Comparing the QNS results [8,9], we can see that the barrier to the H 2 O rotation equal to 29.3 kJ/mol (Phase III) [8] seems to correspond to 24.1 kJ/mol (Phase III) [9]. A general feature of the II-III phase transition is a symmetry reducing the deformation of the water-ligand octahedron [10].…”

Phase Transitions and Water Dynamics of [Co(H2O)6](ClO4)2 and [Mn(H2O)6](BF4)2 Studied by Neutron Scattering Methods

“…For [Co(H20 ) 6](C104)2 we detected by DSC [3] phase transitions at the temperatures: T C1 = 348 K, TC2 = 241 K, and T C3 = 156 K. However, the tem peratures o f the phase transitions were also ascribed to 263 K and 215 K by adiabatic calorimetry [5], to 354 K, 243 K, and 155 K by EPR [6,7], to 156 K by the Mössbauer effect [8], to 160 K by NMR [9], to 166 K by magnetic susceptibility [10,11], to 333 K, 240 K and 166 K by IR and RS [12], and to 344 K, 295 K, 243 K, 182 K, 155 K, 136 K and 121 K by X-ray and dielectric permittivity [13]. For [Mn(H20 ) 6](BF4)2 we detected by DSC [4] the phase transitions at the following temperatures: T r , = 250 K, TC7 = 223 K and T C3 = 162 K.…”