Structural characterization, thermal properties, and molecular motions near the phase transition in hybrid perovskite [(CH2)3(NH3)2]CuCl4 crystals: 1H, 13C, and 14N nuclear magnetic resonance

The structural characterization of the [(CH2](3)(NH3)(2)](+) cation in the perovskite [(CH2)(3)(NH3)(2)]CuCl4 crystal was performed by solid-state H-1 nuclear magnetic resonance (NMR) spectroscopy. The H-1 NMR chemical shifts for NH3 changed more significantly with temperature than those for CH2. This change in cationic motion is enhanced at the N-end of the organic cation, which is fixed to the inorganic layer by N-HCl hydrogen bonds. The C-13 chemical shifts for CH2-1 increase slowly without any anomalous change, while those for CH2-2 move abruptly compared to CH2-1 with increasing temperature. The four peaks of two groups in the N-14 NMR spectra, indicating the presence of a ferroelastic multidomain, were reduced to two peaks of one group near T-C2 (=333 K); the N-14 NMR data clearly indicated changes in atomic configuration at this temperature. In addition, H-1 and C-13 spin-lattice have shorter relaxation times (T-1 rho), in the order of milliseconds because T-1 rho is inversely proportional to the square of the magnetic moment of paramagnetic ions. The T-1 rho values for CH2 and NH3 protons were almost independent of temperature, but the CH2 moiety located in the middle of the N-C-C-C-N bond undergoes tumbling motion according to the Bloembergen-Purcell-Pound theory. Ferroelasticity is the main cause for the phase transition near T-C2.