Phase transition, thermal dissociation and dynamics of NH3 ligands in [Cd(NH3)4](ReO4)2

• Phase transition at Tc = 368.5 K was discovered by means of differential scanning calorimetry.
• The activation energy for deamination process was determined from thermogravimetry data.
• Reorientational motion of NH3 ligands in the low temperature phase was investigated by IR and RS band shape analysis.
• The crystal structure does not change in a wide temperature range.

High temperature phase transition in [Cd(NH3)4](ReO4)2 at Tc = 368.5 K (on heating) was reported for the first time. Thermal stability was investigated by thermal analysis methods. The titled compound decomposes in three main stages. The first two are connected with deamination process whereas in the last step Re2O7 evaporates. The activation energy for NH3 lost processes was estimated from TG measurements. The dynamics of NH3 ligands in the low temperature phase was probed by various complementary techniques. Temperature dependent band shape analysis of properly chosen infrared and Raman scattering vibrational bands was performed. It was found that activation energy for NH3 reorientational motion (below 300 K) is rather small and is equal to ca. 4 kJ mol− 1. The quasielastic neutron scattering measurements revealed that NH3 groups perform fast stochastic reorientational motion even in the low temperatures. The neutron and X-ray powder diffraction data do not revealed any drastic changes in the crystal structure in the wide temperature range.

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