Tuning Order‐Disorder Phase Transition through Regulating the Substituent Group of Anion

Abstract

The structural phase transition compound {[(CH 3 ) 2 CHCH 2 ] 2 NH 2 }•[CF 3 COO] (1) has been synthesized based on the diisobutylamine and trifluoroacetic acid. The DSC data reveal that 1 undergoes a phase transition at 277 K (T c ). When one chlorine atom replaces one fluorine atom on trifluoroacetate anion, three order-disorder phase transitions at 251 K (T 1 ), 282 K (T 2 ) and 290 K could be achieved owing to a stepwise release of rotation motions of the anion and cation in {[(CH 3 ) 2 CHCH 2 ] 2 NH 2 }•[CF 2 ClCOO] (2). Based on the variable temperature crystal structures, the phase transition in compound 1 is triggered by the rotation of three fluorine atoms on the trifluoroacetate anion synchronized with the motions of the methyl groups on the diisobutylammonium cation. However, in compound 2, the phase transitions can be realized by a sequence of motions of both the anion and cation. Besides, the dielectrictemperature dependences were investigated in order to prove this regulation process. All of this investigation will be beneficial to design and synthesis of the novel phase transition materials and molecular dielectric materials on purpose.

Coexistence of Magnetic-Optic-Electric Triple Switching and Thermal Energy Storage in a Multifunctional Plastic Crystal of Trimethylchloromethyl Ammonium Tetrachloroferrate(III)

“…For the past few years, researchers have been working on developing multifunctional materials, which are expected to enhance the capacity and versatility of materials in various applications. − Although a great progress has been made in combining two or three functions in one single molecular material, − it is a huge challenge to combine more than three functions/​responses in one single molecular compound, ,, not to mention integrating multifunction simultaneously at around room temperature. For example, solid–solid phase transition materials could exhibit switchable properties between two different physical states (like magnetic, electrical, optical, and so on), − because they always accompany with sudden changes of their physical and/or chemical properties in response to their temperature fluctuation. These switchable properties could have potential applications in switches, sensors, memory devices, and so on. − Up to now, it is feasible to combine two or three functions in one molecular compound with phase transition, such as in (HIm) 6 ·[MnCl 4 ·​MnCl 6 ] (Im = imidazole) (dielectric and optical switching), dipropyl­ammonium trichloro­acetate (dielectric anomaly and nonlinear optical tristability), phenalenyl-based neutral radical (optical, electrical, and magnetic bistability), and so on.…”

“…For example, solid–solid phase transition materials could exhibit switchable properties between two different physical states (like magnetic, electrical, optical, and so on), − because they always accompany with sudden changes of their physical and/or chemical properties in response to their temperature fluctuation. These switchable properties could have potential applications in switches, sensors, memory devices, and so on. − Up to now, it is feasible to combine two or three functions in one molecular compound with phase transition, such as in (HIm) 6 ·[MnCl 4 ·​MnCl 6 ] (Im = imidazole) (dielectric and optical switching), dipropyl­ammonium trichloro­acetate (dielectric anomaly and nonlinear optical tristability), phenalenyl-based neutral radical (optical, electrical, and magnetic bistability), and so on. However, it is difficult to get more different functions/​responses simultaneously in a molecular phase transition material.…”

“…Thermal energy storage has been a key technology to reduce the time or rate discrepancy between the energy demand and energy supply. During the research on the thermal energy storage of molecular material, it was found that the molecular solid–solid phase transition (including that induced with breaking chemical bonds) material is a new alternative candidate. , Molecular solid–solid phase transition materials as thermal storage materials possess the advantages of no volatilization, small changes in volume, and shape plasticity. − However, general molecular phase transition materials with switchable properties usually suffer small latent enthalpy change, limiting their applications as thermal energy storage materials. − In comparison, the plastic phase transition between a high-symmetric (usually cubic) and a low-symmetric crystal phase usually accompanies with much larger enthalpy change. − Because the plastic phase transition often involves reorientational order–disorder motions of the fragments in their architectures and always exhibits more disordered in the higher temperature cubic phase, which signifies that the plastic crystal was superior than other usual molecular phase transition materials as thermal energy storage materials.…”

Polar Molecule-Based Material with Optic–Electric Switching Constructed by Polar Anions

“…On the basis of the Boltzmann equation ΔS = R ln N (R refers to the gas constant, and N refers to the ratio of numbers of respective geometrically distinguishable orientations), the N is found to be 1.51, 2.24, and 7.11, suggesting three order− disorder phase transitions. 34,35 Different from the phase transitions of 1, 2 undergoes only one pair of phase transitions at around 385 K upon heating and around 362 K upon cooling (Figure 2b). The ΔH, ΔS, and N are 8844 J mol −1 , 23 J mol −1 K −1 , and 15.84, respectively, at 385 K. The larger values of N for 2 suggest a more drastic order−disorder phase transition along with a great structural change.…”

Antimony Bromide Organic–Inorganic Hybrid Compound with a Long-Chain Diamine Showing Switchable Phase Transition and Second-Harmonic Generation Properties

“…The one-dimensional (1D) structural arrangement of the inorganic anionic framework in organic–inorganic hybrid metal halides provides a dynamic motion of organic cations. This unique arrangement enables materials to respond to changes in external temperature or pressure, which leads to the generation of phase transitions or second-harmonic generation (SHG) signals. − Monoamines are somewhat limited in the tuning and design of organic–inorganic hybrid metal halide structures due to their relatively simple molecular structure. On the other hand, at high temperatures, the materials synthesized from monoamines may undergo dissolution or loss of crystallization, which adversely affects the thermal stability, − and the photovoltaic properties are also somewhat limited.…”