A High-Temperature Order-Disorder Phase Transition Coupled With Conformational Change in the Hybrid Material [C6H13NH]2⋅ZnBr4

A new high-temperature, hybrid, phase-transition material, 1-methylpiperidinium tetrabromozincate (1), that shows a reversible transition at 345 K was synthesized. Differential scanning calorimetry and specific heat capacity measurements confirmed this reversible transformation with a large heat hysteresis of 25 K, which describes a typical first-order phase transition in 1. The dielectric constant exhibited a steplike anomaly and showed high and low dielectric states in the high- and room-temperature phases, respectively, and therefore, this hybrid might be considered as a potential switchable dielectric material. The variable-temperature powder X-ray diffraction patterns displayed remarkable shifts between the experimental patterns at the two different phases. Single-crystal X-ray diffraction analyses at various temperatures revealed that the origin of this transformation could be attributed to disordering of the bromine atoms in the anion and the nitrogen atom of the cation. The cation also assumed a conformational change, which was likely induced by the disordered nitrogen atom. The conformational onset of the transformation of the cation from a planar conformer into a relaxed chair also occurred upon decreasing the temperature below transition point; thus, the combined order-disorder and conformational change induced the structural transformation and the change in symmetry.