Abstract
The series of MeA2KFe(CN)6, where MeA=CH3NH3+, (CH3)2NH2+, (CH3)3NH+ and (CH3)4N+, has been studied by IR and Raman spectroscopy as the function of temperature in order to elucidate the mechanisms of the phase transitions. The order-disorder process has been confirmed in all cases. Different models have been proposed based on the dynamic effects observed in the spectra. The crystal containing (CH3)2NH2+ cations constitutes a model with melt-like thermal behavior and strongly temperature-influenced hydrogen bonding. In the case of sample with (CH3)4N+ an unperturbed rotation of these cations is observed, while in the crystals with methyl- and trimethylammonium cations the hydrogen bonds acting as positional stabilizers prevent the organic cation from a completely free motion. Additionally, the statistical disorder of dimethyl- and trimethylammonium cations has been confirmed by the thermal evolution of the FWHM of the related bands.
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