Structure and molecular dynamics of perovskite N(CH₃)₄MnCl₃ crystals of high-temperature phases I and (I')

New developments in perovskite-type N(CH₃)₄MnCl₃ single crystals were examined, with a focus on their high-temperature phases. The phase transition temperature (T_C) was established as being 390 K via differential scanning calorimetry and powder X-ray diffraction analyses. At 300 K, the single-crystal structure has hexagonal symmetry and exhibits thermal stability up to a high temperature of approximately 680 K. Additionally, ¹H and ¹³C nuclear magnetic resonance (NMR) chemical shifts displayed continuous changes with temperature, without any anomalous behavior observed near T_C. The ¹H spin-lattice relaxation time, which represents the molecular motion of ¹H, shows slight changes near T_C. The phase transition from phase I to I ('), associated with changes in the rotational degrees of freedom of N(CH₃)₄⁺ molecules, is considered second-order. The small change between phases I and I (') is consistent with a change in the space group in the same hexagonal structure previously reported. These physical properties indicate the potential applications of N(CH₃)₄MnCl₃ as an organic-inorganic hybrid perovskite material.