Phase transition and cationic motion in the perovskite formate framework [(CH3)(2)NH2][Mg(HCOO)(3)]

作者：Asaji Tetsuo^*; Yoshitake Sho; Ito Yoshiharu; Fujimori Hiroki

来源：Journal of Molecular Structure, 2014, 1076: 719-723.

DOI：10.1016/j.molstruc.2014.08.037

• NMR
• Spin-lattice relaxation
• Phase transition
• Metal-organic framework

The dielectric phase transition of a metal-organic perovskite with a dimethylammonium cation, [(CH3)(2)NH2][Mg(HCOO)(3)], at T-c = 270 K was investigated using H-1 nuclear magnetic resonance spectroscopy. The temperature dependence of the spin-lattice relaxation time T-1, was measured to elucidate the methyl group reorientation and cation reorientation. The results was very similar to that of the zinc analog, [(CH3)(2)NH2][Zn(HCOO)(3)], Previously reported. The cationic motion was expected to be the 120 degrees reorientation of the dimethylammonium ion around the axis through the two carbon atoms of the cation. The activation energy for cationic motion was determined to be 22.7 kJ mol(-1). The two methyl groups of the cation in the low-temperature phase become nonequivalent and have activation energies of 9.1 and 7.0 kJ mol(-1) for reorientation about the methyl group C-3-axis. The T-1 measurements indicated that the T-c = 270 K phase transition is of first-order and another first-order phase transition was revealed at around 80K. The transition entropy was estimated to be Delta S = 10 +/- 1 J K-1 mol(-1) for the T-c = 270 K phase transition in agreement with the simple three fold order-disorder model of dimethylammonium ion.

• 出版日期2014-11-5