A Promising Phase Change Material with Record High Ionic Conductivity over a Wide Temperature Range of a Plastic Crystal Phase and Magnetic Thermal Memory Effect.

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)] (; [EMIm] = 1-ethyl-3-methylimidazolium and mnt = maleonitriledithiolate), and its crystal consists of twin dimeric chains of [Ni(mnt)] 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 , characterized by variable temperature powder X-ray diffraction (PXRD) and optical microscopy images, spans a broad temperature range with Δ ∼123/153 K on heating/cooling (DSC measurement), and the wide Δ 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. is a single-component ion plastic crystal with a record high ion conductivity, 0.21 S·cm, at 453 K. The crystal-to-plastic crystal transformation in 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.