Vibrational investigation of pressure- and temperature-induced phase transitions in metal formates templated by ethylammonium ions

We report for the first time phonon properties of [CH3CH2NH3][Mg(HCOO)(3)] (EtAMg). The studied compound undergoes two structural temperature-induced phase transitions and temperature-dependent Raman and infrared studies let us to obtain insight into mechanism of these transitions. In particular, very large broadening of infrared and Raman bands, attributed to vibrations of the NH3 groups, revealed highly dynamic nature of these groups in the both high-temperature phases. This result indicates that the phase transitions at 374 and 426K are associated with disordering of the template cations. Raman and infrared data also show that both phase transitions are accompanied by significant distortion of the anionic framework. We also present the pressure-dependent Raman data of EtAMn framework up to 7.1GPa. These data revealed presence of two pressure-induced phase transitions, one between 3.7 and 4.0GPa and second between 5.6 and 6.0GPa. We discuss mechanisms of these transitions. Copyright (c) 2017 John Wiley & Sons, Ltd.