Ionic dynamics of the cation in organic–inorganic hybrid compound (CH3NH3)2MCl4 (M = Cu and Zn) by 1H MAS NMR, 13C CP MAS NMR, and 14N NMR

Abstract

The ionic dynamics of (CH₃NH₃)₂MCl₄ (M = Cu, Zn) by ¹H magic-angle spinning (MAS) nuclear magnetic resonance (NMR), ¹³C cross-polarization (CP) MAS NMR, and ¹⁴N NMR are investigated as a function of temperature with a focus on the role of the CH₃NH₃⁺ cation. The molecular motions in (CH₃NH₃)₂MCl₄ are also discussed based on the ¹H spin–lattice relaxation time in the rotating coordinate frame T_1ρ. From the ¹H T_1ρ results, the activation energies for the tumbling motion of ¹H for CH₃ and NH₃ were similar, and the uniaxial rotations occurred within a large temperature range. The molecular motions for ¹³C and ¹⁴N of the main chain in the CH₃NH₃⁺ cation were rigid, whereas those for ¹H of the side chain in the CH₃NH₃⁺ cation were very free at high temperatures. T_1ρ provides insight into the changes in the cation reorientation rates induced by heating at high temperatures.