Reversible structural phase transitions and switchable dielectric behaviours in a cyanometallate-based double perovskite-type cage compound: [C3H4NS]2[KCo(CN)6]
A new cyanometallate-based double perovskite-type compound has been synthesized with the formula of (HTz)2[KCo(CN)6] (HTz = thiazolium cation, 1). The basic building units of the framework are Co(CN)6 and K ions. The K ion coordinates with six adjacent cyanide N atoms that form a regular octahedral geometry. Meanwhile, the HTz rings are existed in the cage. It undergoes two-step reversible structural phase transitions at 237 K and 210 K, respectively, along with switchable dielectric transformation. Variable-temperature single-crystal structural analysis reveals that relatively small displacements and/or thermal vibrations of the HTz rings are the origin of the phase transitions. Meanwhile, the switchable dielectric constant of 1, i.e., means a dielectric transition between low-dielectric state (switch off) and high-dielectric state (switch on). This character may enrich the family of stimuli-responsive materials and find potential applications in switchable dielectric materials.