Dielectric Phase Transition Behavior in an N-salicyliden Based Ion Crystal

A new Schiff base iodides with a formula of [o-OH-Bz-1-APy]I have been synthesized and characterized structurally (o-OH-Bz-1-APy+ = ortho-hydroxy-benzylidene-1-aminopyridinium Schiff base derivative (1)). Two adjacent cations adopt an antiparallel arrangement forming π-type cation dimmer, along the a-axis direction, the cation dimmer formed irregular cation stacks and counterion I− anions are embedded in the cation stacks in the crystals of 1. A strong frequency dispersion of e’ is observed in the low frequency region and can be attributed to local dipole motion in 1. Furthermore, this ion-pair compound shows novel dielectric phase transition around 125 °C. DSC measurement of 1 exhibited gradual endothermic peak around the transition temperature and small enthalpy change means that the difference in lattice energy between the two phases is very small. This study provided a new strategy for the design of dielectric phase transition system. Compound 1 shows a strong frequency dispersion of dielectric loss in the low frequency region and novel dielectric phase transition.