Raman light scattering, infrared absorption and neutron scattering studies of the phase transition and reorientational dynamics of H2O ligands and ClO4↙ anions in [Ca(H2O)4](ClO4)2✠

Vibrational-reorientational dynamics of H2O ligands and ClO4↙ anions in the high-, intermediate- and low-temperature phases of [Ca(H2O)4](ClO4)2, detected previously by differential scanning calorimetry (DSC) method, were investigated. The following experimental methods were applied to achieve the goal: middle-infrared (FT-MIR), Raman spectroscopy (RS) and inelastic incoherent neutron scattering (IINS). FT-MIR and RS spectra versus temperature show distinct changes in full-width-at-half-maximum (FWHM) of some bands connected with vibrational modes of ClO4↙ and [Ca(H2O)4]2+ ions. It suggests that in the high temperature phase these ions (and also the ligands from complex cation) perform fast (picoseconds correlation time scale, which is characteristic for optical spectroscopy) stochastic reorientational motions, however in the lower temperatures the speed of these motions is slowed down. Moreover, the splitting of some bands accompanying the observed phase transitions. The comparison of the results obtained by these complementary methods was made. Additionally, IR, RS and IINS spectra were calculated by the DFT method and an excellent agreement with the experimental data was obtained using CASTEP plane-wave periodic boundary condition code. The bands were assigned based on analysis of the phonon eigenvectors obtained from CASTEP calculations.