Phase transitions in (C₇H₁₂N₂)₂[SnCl₆]Cl₂·1.5H₂O crystal, studied by NMR and infrared spectroscopy

Abstract

The (C 7 H 12 N 2 ) 2 [SnCl 6 ]Cl 2 ·1.5H 2 O complex is a new member of the family of hybrid organic-inorganic perovskite compounds. It exhibits two orderdisorder phase transitions with changes in the conformation of aromatic cations at the two transition temperatures 360 and 412 K. Differential scanning calorimetry, nuclear magnetic resonance (NMR), and Fourier-transform infrared (FT-IR) spectroscopy were used to investigate these phase transitions. These transition mechanisms were investigated in terms of the spin-lattice relaxation times T1 for 1 H static NMR and the chemical shifts for 13 C CP-MAS. The temperature dependence of T1( 1 H) and 13 C chemical shifts are changed near T C1 and T C2 . Furthermore, the splitting for 13 C NMR signals in Phases (II) and (III) indicated a ferroelastic characteristic of the compound. In addition, FT-IR results indicate that the ordered conformational structure of aromatic cations undergoes a remarkable disorder with increasing temperature. The NMR and FT-IR studies suggest that the phase transition mechanisms are related to the reorientational motion of [C 7 H 12 N 2 ] 2+ cations as a whole. Phase transition was examined in light of the interesting optical properties of this material.