Infrared and Raman studies of water molecule normal vibrations in crystalline hydrates which form the chain structures

Infrared and Raman spectra of aqua-pentachloro-complexes (M2I[FeCl5(H2O)] (MI=K+, Rb+), M2I[InCl5(H2O)] (MI=K+, Rb+, Cs+)) and their partially deuterated analogues have been studied in the range 100–4000 cm−1, at room (RT) and liquid-nitrogen (LNT) temperature. In the vibrational spectra of these compounds, the following spectral effects were observed: (a) low HOH bending frequencies, (b) simultaneous shift of OH stretching and HOH bending bands towards lower frequencies at LNT, (c) mixing of libration modes. Moreover a strong influence of central cations (MIII) and alkali cations (MI) on the frequency of water molecule normal vibrations was noticed. A detailed analysis of structural and spectral data suggests that above mentioned effects may be correlated with the chain structure of studied monohydrates.