Phase transition sequence in (C5H11NH3)2ZnCl4 between 55 and 355 K

Abstract Bis-penthylammoniun tetrachloro zincate (C 5 H 11 NH 3 ) 2 ZnCl 4 , was investigated between 55 K and 355 K by means of adiabatic calorimetry, thermal expansion and optical measurements. The following phase transition sequence was found: V-(141.5K)-IV-(148K)-III-(249.6K)-II-(349K)-I, and the associated thermodynamic functions were obtained. The two lower phase transitions are probably connected with order-disorder mechanisms associated with hydrogen bonds. Phase III is pure proper gyrotropic and phase I is characterized by a high confonnational disorder. The various energy contributions in phase I were estimated in order to give a qualitative description of the molecular movements in the II-I phase transition.