Plastic crystals show diverse functional properties, for example, resemblance to a liquid with internal rotation degrees of freedom, the colossal barocaloric effect (BCE), excellent ion conduction, huge enthalpy changes between phase transition of the crystal and plastic crystal, and so forth. These unique natures endow plastic crystals with a range of applications in the material areas of the BCE and solid-state thermal energy storage, solid electrolytes, and solid-state “solvent” for ion doping. Herein, we present the study of DSC, temperature-dependent powder X-ray diffraction, and ion conduction for an organic ion plastic crystal, TBA2[Ni­(mnt)2] (1; TBA+ = tetra-n-butylammonium, mnt2– = maleonitriledithiolate). Upon heating, 1 undergoes a crystal-to-plastic crystal transition at ∼398 K and a plastic crystal-to-plastic crystal transformation at ∼415 K. The annealing process cooled from the plastic crystal state induces a series of reversible solid–solid phase transitions, related to the conformation transformation of alkyl chains in cations; amongst them, an exothermic solid–solid phase transition occurs at ∼324 K, releasing huge latent heat during heating process, which is in contrast to most observations, and such a material releasing large latent heat near room temperature has promising application in thermal energy storage. Additionally, two plastic crystal phases in 1 extend from 398 to 473 K at least (1 starts to decompose around 500 K), with a wide temperature window and high ion conductivity of 10–3 to 10–2 S·cm–1, indicating that 1 is a good ion conductor.

The emerging organic ion plastic crystals (OIPCs) are the most promising candidates used as solid-state electrolytes in a range of ionic devices. To endow an OIPC with additional functionality may create a new type of material for multifunctional devices. Herein, we present an ion plastic crystal, [EMIm]­[Ni­(mnt)2] (1; [EMIm]+ = 1-ethyl-3-methylimidazolium and mnt2– = maleonitriledithiolate), and its crystal consists of twin dimeric chains of [Ni­(mnt)2]− anions, embraced by [EMIm]+ cations. A crystal-to-plastic crystal transformation with a large latent heat that occurred at ∼367/337 K on heating/cooling is confirmed by the differential scanning calorimetry (DSC) technique. The plastic crystal phase in 1, characterized by variable temperature powder X-ray diffraction (PXRD) and optical microscopy images, spans a broad temperature range with ΔT ∼123/153 K on heating/cooling (DSC measurement), and the wide ΔT is relevant to an extra stable anion chain owing to the strong antiferromagnetic (AFM) interactions protecting the chain from collapse in the plastic crystal state. 1 is a single-component ion plastic crystal with a record high ion conductivity, 0.21 S·cm–1, at 453 K. The crystal-to-plastic crystal transformation in 1 is coupled to a bistable magnetic transition to give a multi-in-one multifunctional material. This study provides a creative thought for the design of OIPCs with striking thermal, electrical, and magnetic multifunctionality.

A rotorlike supramolecular crystal, {[K­(18-crown-6)]­PbI3}∞, is composed of a linear [PbI3]∞ chain acting as a stator and [K­(18-crown-6)]+ cations fastened to the [PbI3]∞ chain and K–I bond like rotators and axes, respectively. A reversible breaking-symmetry phase transition occurs at ∼305 K. Variable-temperature 1H NMR spectra and dielectrics were used for the dynamic analysis of [K­(18-crown-6)]+ cations in the crystal.

An organometallic supramolecular crystal of {K(18-crown-6)(ηn-C6H5B(C6H5)3)} (n = 1–6) has a half-sandwich structure and exhibits a reversible breaking-symmetry phase transition and switchable dielectric behavior.

Organic ion plastic crystals (OIPCs) show promising applications in various all- solid-state electrochemical energy storage devices. In this regard, superionic conducting OIPCs with broad temperature window are highly demanded. Herein,...