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Dielectric relaxations have widely applied on high permittivity capacitors, dielectric switches, ferroelectrics, pyroelectrics, and electrical insulating materials. However, few investigations of large dielectric relaxation behaviors on organic−inorganic hybrid materials have been documented before. Here we present a novel two-dimensional succinimide lithium(I) hybrid compound, [Li(PDD) 2 ClO 4 ] n , 1, (PDD = 2,5-pyrrolidinedione = succinimide) which shows reversible phase transition behavior in the vicinity of 228 K accompanied by an unusual symmetry breaking from I4 1 /amd to C2/c. X-ray single crystal diffractions analysis indicates the twist motion of pyrrolidine heterocycles, and order−disorder motion of ClO 4 − anions triggered the reversible phase transition. By means of an intuitive crystallographic model (rattling ion model), we further illustrated the mechanism of the interesting reversible phase transition. Particularly, 1 shows ultralarge dielectric relaxation behavior in the vicinity of the phase transition by its dielectric constant dependence on temperatures and frequencies as well as its Cole−Cole relation.

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The molecular multi‐sequential phase transition accompanying with perfect switchable dielectric behaviors and ferroelastic properties are seldom reported. Here we investigated unusual two‐step reversible structural phase transitions which consist of a ferroelastic phase transition and a special structural phase transition without symmetry breaking in a simple clathrate of 18‐Crown‐6 phosphofluoric acid monohydrate, (1). The further molecular dynamic by variable temperature X‐ray Single crystal diffraction and Powder X‐ray diffractions were disclosed that it was driven by two distinct rotation motions namely compass‐like rotation and windlass‐like rotation. Two pairs of distinct reversible step‐like dielectric anomalies with electrical tristabilities among high, middle and low dielectric states at 278/281 K and 292/296 K in heating/cooling runs suggest that it can be a potential switchable dielectric molecular material within a narrow temperaturespan (15 K). The DSC curves show analogous heat anomalies at the same temperatures and further confirm the reversible phase transition behaviors.

Solid-to solid-state reversible phase transitions are widely used in switchable dielectrics, ferroelectrics, piezoelectrics, and pyroelectric and non-linear optical materials. Herein we report a new crown ether clathrate, [Habf-(18-crown-6)] [PF] (Habf = p-ammonium benzene formamide) which shows an interesting reversible phase transition near room temperature (263 K). X-ray single crystal diffraction analysis shows that the synergetic rotation motion between the 18-crown-6 crown ethers and the order-disorder motions of both hexafluorophosphate guest anions and 18-crown-6 crown ether host molecules lead to the phase transition. This reversible phase transition is confirmed by an evident thermal anomaly behavior around 263 K. The apparent step-like dielectric change around the phase transition indicates that it has potential application in dielectric switches.

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