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)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.