Phase transitions in (C 7 H 12 N 2 ) 2 [SnCl 6 ]Cl 2 ·1.5H 2 O crystal, studied by NMR and infrared spectroscopy

The (C H N ) [SnCl ]Cl ·1.5H O complex is a new member of the family of hybrid organic-inorganic perovskite compounds. It exhibits two order-disorder 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 H static NMR and the chemical shifts for C CP-MAS. The temperature dependence of T1( H) and C chemical shifts are changed near T and T . Furthermore, the splitting for 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 H N ] cations as a whole. Phase transition was examined in light of the interesting optical properties of this material.