TY - JOUR
T1 - Phase transition and cationic motion in the perovskite formate framework [(CH3)2NH2][Mg(HCOO)3]
AU - Asaji, Tetsuo
AU - Yoshitake, Sho
AU - Ito, Yoshiharu
AU - Fujimori, Hiroki
N1 - Publisher Copyright:
© 2014 Elsevier B.V. All rights reserved.
PY - 2014/11/5
Y1 - 2014/11/5
N2 - The dielectric phase transition of a metal-organic perovskite with a dimethylammonium cation, [(CH3)2NH2][Mg(HCOO)3], at Tc = 270 K was investigated using 1H nuclear magnetic resonance spectroscopy. The temperature dependence of the spin-lattice relaxation time T1, was measured to elucidate the methyl group reorientation and cation reorientation. The results was very similar to that of the zinc analog, [(CH3)2NH2][Zn(HCOO)3], previously reported. The cationic motion was expected to be the 120° 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 C3-axis. The T1 measurements indicated that the Tc = 270 K phase transition is of first-order and another first-order phase transition was revealed at around 80 K. The transition entropy was estimated to be ΔS = 10 ± 1 J K-1 mol-1 for the Tc = 270 K phase transition in agreement with the simple three fold order-disorder model of dimethylammonium ion.
AB - The dielectric phase transition of a metal-organic perovskite with a dimethylammonium cation, [(CH3)2NH2][Mg(HCOO)3], at Tc = 270 K was investigated using 1H nuclear magnetic resonance spectroscopy. The temperature dependence of the spin-lattice relaxation time T1, was measured to elucidate the methyl group reorientation and cation reorientation. The results was very similar to that of the zinc analog, [(CH3)2NH2][Zn(HCOO)3], previously reported. The cationic motion was expected to be the 120° 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 C3-axis. The T1 measurements indicated that the Tc = 270 K phase transition is of first-order and another first-order phase transition was revealed at around 80 K. The transition entropy was estimated to be ΔS = 10 ± 1 J K-1 mol-1 for the Tc = 270 K phase transition in agreement with the simple three fold order-disorder model of dimethylammonium ion.
KW - Metal-organic framework
KW - NMR
KW - Phase transition
KW - Spin-lattice relaxation
UR - http://www.scopus.com/inward/record.url?scp=84910098080&partnerID=8YFLogxK
U2 - 10.1016/j.molstruc.2014.08.037
DO - 10.1016/j.molstruc.2014.08.037
M3 - Article
AN - SCOPUS:84910098080
SN - 0022-2860
VL - 1076
SP - 719
EP - 723
JO - Journal of Molecular Structure
JF - Journal of Molecular Structure
ER -