Phase transitions in (C7 H12 N2 )2 [SnCl6 ]Cl2 ·1.5H2 O crystal, studied by NMR and infrared spectroscopy

The (C7 H12 N2 )2 [SnCl6 ]Cl2 ·1.5H2 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 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 TC1 and TC2 . 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 [C7 H12 N2 ]2+ cations as a whole. Phase transition was examined in light of the interesting optical properties of this material.