Cation dynamics by 1H and 13C MAS NMR in hybrid organic-inorganic (CH3CH2NH3)2CuCl4

To understand the dynamics of the cation in layered perovskite-type (CH3CH2NH3)2CuCl4, the temperature-dependent chemical shifts and spin-lattice relaxation times T 1ρ in the rotating frame have been measured using 1H magic angle spinning nuclear magnetic resonance (MAS NMR) and 13C cross-polarization (CP)/MAS NMR techniques. Each proton and carbon in the (CH3CH2NH3)+ cation is distinguished in MAS NMR spectra. The Bloembergen-Purcell-Pound (BPP) curves for 1H T 1ρ in CH3CH2 and NH3, and for the 13C T 1ρ in CH3 and CH2 are revealed to have minima at low temperatures. This implies that the curves represent the CH3 and NH3 + rotational motions. The amplitude of the cationic motion is enhanced at the C-end, that is, the N-end of the organic cation is fixed to the inorganic layer through N-H⋯Cl hydrogen bonds, and T 1ρ becomes short with larger-amplitude molecular motions.

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

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.