Structural phase transition in catena-(1,2,3,6-tetrahydropyridine tris(μ2-chloro)-cadmium(II))

The title compound, catena-(1,2,3,6-tetrahydropyridine tris(μ2-chloro)-cadmium(II)), has a hexagonal perovskite-type structure with formula AMX3. It undergoes a reversible dielectric transition at about 197 K. The transition was accompanied by significant dielectric anomaly, and was confirmed by DSC measurements. The variable-temperature single crystal X-ray diffraction analysis reveals that the transition is a process of the doubling of the cell volume from P21/m to P21/a. The transition is caused by the order–disorder change of the 1,2,3,6-tetrahydropyridinium cation.