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

Abstract

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.