Reversible structural phase transition of pyridinium-4-carboxylic acid perchlorate

Crystal Structure and Phase Transition of the C–H···F–H-Bonded Supramolecular Compound with 4-Nitroanilinium Based on 18-Crown-6

A novel inorganic-organic hybrid supramolecular macrocyclic compound, (4-nitroanilinium)(18-crown-6)(PF6)(1), was synthesized and characterized by infrared spectroscopy, thermogravimetric analysis, elemental analysis, differential scanning calorimetry (DSC), and single-crystal X-ray diffraction. Crystal 1 is found to comprise 1D C–H···F–P hydrogen-bonded chains of (4-nitroanilinium+)(18-crown-6) supramolecular cations and PF6− anions. DSC measurements confirm that 1 undergoes a reversible phase transition at 255 K with a hysteresis width of 6 K. A strong dielectric response is observed above 250 K at a low frequency (500 Hz), suggesting the occurrence of proton transfer in the C–H···F–P hydrogen bonds. A precise analysis on the main packing and structural differences, as well as the changes in the intermolecular interaction between the low- and high-temperature phases, reveals that C–H···F–P hydrogen bonds are the main factors affecting phase transition and dielectric behavior.

Reversible phase transition of 2-carboxypyridinium perchlorate-pyridinium-2-carboxylate (1/1)

The title salt, C6H6NO2(+)·ClO4(-)·C6H5NO2, was crystallized from an aqueous solution of equimolar quantities of perchloric acid and pyridine-2-carboxylic acid. Differential scanning calorimetry (DSC) measurements show that the compound undergoes a reversible phase transition at about 261.7 K, with a wide heat hysteresis of 21.9 K. The lower-temperature polymorph (denoted LT; T = 223 K) crystallizes in the space group C2/c, while the higher-temperature polymorph (denoted RT; T = 296 K) crystallizes in the space group P2/c. The relationship between these two phases can be described as: 2a(RT) = a(LT); 2b(RT) = b(LT); c(RT) = c(LT). The crystal structure contains an infinite zigzag hydrogen-bonded chain network of 2-carboxypyridinium cations. The most distinct difference between the higher (RT) and lower (LT) temperature phases is the change in dihedral angle between the planes of the carboxylic acid group and the pyridinium ring, which leads to the formation of different ten-membered hydrogen-bonded rings. In the RT phase, both the perchlorate anions and the hydrogen-bonded H atom within the carboxylic acid group are disordered. The disordered H atom is located on a twofold rotation axis. In the LT phase, the asymmetric unit is composed of two 2-carboxypyridinium cations, half an ordered perchlorate anion with ideal tetrahedral geometry and a disordered perchlorate anion. The phase transition is attributable to the order-disorder transition of half of the perchlorate anions.

A high-temperature supramolecular-based switchable dielectric material with electrical bistability between high and low dielectric states

One new hybrid supramolecular-based phase transition compound TAPC containing macrocycle stator with electrical bistability between high and low dielectric states has been prepared.

Temperature-induced reversible structural phase transition of 1,4-dimethyl-1,4-diazabicyclo[2.2.2]octane bis(perchlorate)

A novel molecular-based phase change material was synthesized. The phase transition from a room temperature to a low temperature paraelectric phase might be driven by the order–disorder transition of ClO4⁻ anions and the ordering of twisting motions of the dabco ring.

Tris(3-methyl-anilinium) tetra-chlorido-zincate chloride hemihydrate

The asymmetric unit of the title compound, (C₇H₁₀N)₃[ZnCl₄]Cl·0.5H₂O, consists of three 3-methyl­anilinium cations, one tetrahedral tetra­chloridozincate anion and one chloride anion and a water mol­ecule, which lies on a twofold axis. The components are linked into chains parallel to the a axis by N—H⋯Cl hydrogen bonds.

3-Methyl-anilinium hydrogen phthalate

The asymmetric unit of the title salt, C₇H₁₀N⁺·C₈H₅O₄⁻, consists of two 3-methyl­phenyl­ammonium cations and two hydrogen phthalate anions. There are strong intra­molecular O—H⋯O hydrogen bonds in the virtually planar (r.m.s. deviations = 0.054 Å) phthalate anions. In the crystal, the cations and anions are connected via an extensive sytem of N—H⋯O hydrogen bonds into a corrugated layer extended parallel to (001).

Metal-organic complex ferroelectrics

Ferroelectric materials are of importance and interest in both fundamental scientific research and various technological applications. Metal-organic complexes (MOCs) represent a class of molecule-based ferroelectrics, which have shown various properties or functionalities due to their hybrid inorganic-organic nature. This tutorial review shows the recent development of the MOC ferroelectrics with particular emphases on the mechanism of ferroelectric-to-paraelectric phase transition, symmetry consideration, and multifunctionality.