Ion Conduction and Complicated Phase Transition Behaviors in an Organic Ion Plastic Crystal, [Tetra-n-butylammonium]₂[Ni(maleonitriledithiolate)₂]

Abstract

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.

Formation of organic ion cocrystals, phase transition and ion conduction

“…25) and Bu (ref. 22 and 25) have been reported, and the crystal structures of Me and Et are re-determined in this work, and the structural data are in agreement with previously reported ones. Three compounds crystallize in the triclinic space group P 1̄, and an asymmetric unit contains half a planar [Ni(mnt) 2 ] 2− anion together with one quaternary ammonium cation.…”

“…In our previous study, the features of phase transition and ion conduction were investigated for Bu , 22 and in this study, the thermotropic phase transition behaviors of Me , Et , Pr , MeEt , MeBu and EtBu by the DSC technique (Fig. 5 and 6) and temperature-dependent crystal morphologies using hot stage polarized optical microscopy (POM; Fig.…”

“…The planar metal bis-1,2-dithiolene [M(dithiolato) 2 ] n − anions (M = Ni, Pd, or Pt ion; n = 1 or 2) seem to meet this criterion because the negative charge is distributed over the whole molecular skeleton of the [M(dithiolato) 2 ] n − anion due to π-electron delocalization, significantly reducing the interionic Coulombic interactions and lattice energy. Recently, we have explored the possibility of developing OIPCs of [M(dithiolato) 2 ] n − anions with conventional globular cations, and we have really achieved superior ion-conducting OIPCs, [EMIm][Ni(mnt) 2 ] 21 and [TBA] 2 [Ni(mnt) 2 ], 22 where EMIm + and TBA + represent the globular cations 1-ethyl-3-methylimidazolium and tetra- n -butylammonium, respectively. In the plastic crystal phase, the ion conductivity increases with rising temperature from 10 −2 to 10 −1 S cm −1 in range of 367–453 K for [EMIm][Ni(mnt) 2 ] and from 10 −3 to 10 −2 S cm −1 in range of 398–473 K for TBA 2 [Ni(mnt) 2 ].…”

2D Lead Iodide Perovskite with Mercaptan-Containing Amine and Its Exceptional Water Stability

“…The enthalpy of the reaction (eq ) can be obtained based on thermodynamic calculation (see the SI). The calculated Δ H is 3.28 kJ/mol, and this value should be reasonable for the reversible phase transition at room temperature (<30 °C) by consulting the reported enthalpies and temperatures of phase transition. , Based on the structural analysis (Figure , torsion angles in Table S3), the HCya cations undergo configuration rotation at higher temperature, which changes the red phase to yellow phase.…”

Magnetic bistable organic ionic plastic crystal with room temperature ion conductivity comparable to NASICON and superionic conduction in a broad temperature window

“…The reported high ionic conducting plastic crystals are summarized in Table S8 (ESI †), and compared with them, 1 shows the highest recorded ionic conductivity in the plastic phase. 18,25,32,[35][36][37][38][39][40][41][42][43][44][45][46][47][48] The activation energy of ion migration is estimated according to the Arrhenius equation,…”