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.

ABSTRACT: The structural characterization of the [(CH₂]₃(NH₃)₂]⁺ cation in the perovskite [(CH₂)₃(NH₃)₂]CuCl₄ crystal was performed by solid-state ¹H nuclear magnetic resonance (NMR) spectroscopy. The ¹H 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-H···Cl hydrogen bonds. The ¹³C 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 ¹⁴N NMR spectra, indicating the presence of a ferroelastic multidomain, were reduced to two peaks of one group near T_C2 (=?333 K); the ¹⁴N NMR data clearly indicated changes in atomic configuration at this temperature. In addition, ¹H and ¹³C spin-lattice have shorter relaxation times (T_1?), in the order of milliseconds because T_1? is inversely proportional to the square of the magnetic moment of paramagnetic ions. The T_1? 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.

SUBMITTER: Lim AR 

PROVIDER: S-EPMC7705681 | biostudies-literature | 2020 Nov

REPOSITORIES: biostudies-literature