Structural characterization, thermal properties, and molecular motions near the phase transition in hybrid perovskite [(CH(2))(3)(NH(3))(2)]CuCl(4) crystals: (1)H, (13)C, and (14)N nuclear magnetic resonance

The structural characterization of the [(CH(2)](3)(NH(3))(2)](+) cation in the perovskite [(CH(2))(3)(NH(3))(2)]CuCl(4) crystal was performed by solid-state (1)H nuclear magnetic resonance (NMR) spectroscopy. The (1)H NMR chemical shifts for NH(3) changed more significantly with temperature than those for CH(2). This change in cationic motion is enhanced at the N-end of the organic cation, which is fixed to the inorganic layer by N–H···Cl hydrogen bonds. The (13)C chemical shifts for CH(2)-1 increase slowly without any anomalous change, while those for CH(2)-2 move abruptly compared to CH(2)-1 with increasing temperature. The four peaks of two groups in the (14)N NMR spectra, indicating the presence of a ferroelastic multidomain, were reduced to two peaks of one group near T(C2) (= 333 K); the (14)N NMR data clearly indicated changes in atomic configuration at this temperature. In addition, (1)H and (13)C spin–lattice have shorter relaxation times (T(1ρ)), in the order of milliseconds because T(1ρ) is inversely proportional to the square of the magnetic moment of paramagnetic ions. The T(1ρ) values for CH(2) and NH(3) protons were almost independent of temperature, but the CH(2) 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).