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
Ae Ran Lim
Abstract
Abstract 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 .