Inorganic Anions Regulate the Phase Transition in Two Organic Cation Salts Containing [(4-Nitroanilinium)(18-crown-6)]+ Supramolecules

Nonlinear optical (NLO) switchable materials have attracted intense attention because of their promising applications in optoelectronic devices. However, previous studies are mainly limited to mole...

The crystal structure of the crystalline 1 : 1 complex of 2,4,6-trimethylaniline with perchloric acid, (C9H14N)+·ClO4− (1), was determined at 25 °C and 110 °C, respectively. The crystal structural analysis of both temperatures show that 1 undergoes a reversible phase transition from triclinic P (No.2) to monoclinic P21/m (No.11) with a distinct change of the cell parameters. It is a ferroelastic phase transition with an Aizu notation of 2/mF. DSC (differential scanning calorimetry) measurement confirms that this compound undergoes a reversible first-order solid-state structural phase transition at about 48 °C with a thermal hysteresis of 3 °C. Usually, phase transition is accompanied by an anomaly of the dielectric constant near phase transition temperature (Tc). The DSC measurement, temperature-dependent single-crystal X-ray diffraction and dielectric studies reveal that 1 displays structural phase transitions and distinctly step-like dielectric anomalies at 48 °C probably supporting that this phase transition is of the first-order.

Above room-temperature dielectric switching in a new Zn-halide hybrid crystal based on pyrrolidine-derivative

Human LDL undergoes a reversible thermal order-disorder phase transition associated with the cholesterol ester packing in the lipid core. Structural changes associated with this phase transition have been shown to affect the resistance of LDL to oxidation in vitro studies. Previous electron cryo-microscopy studies have provided image evidence that the cholesterol ester is packed in three flat layers in the core at temperatures below the phase transition. To study changes in lipid packing, overall structure and particle morphology in three dimensions (3D) subsequent to the phase transition, we cryo-preserved human LDL at a temperature above phase transition (53°C) and examined the sample by electron microscopy and image reconstruction. The LDL frozen from 53°C adopted a different morphology. The central density layer was disrupted and the outer two layers formed a "disrupted shell"-shaped density, located concentrically underneath the surface density of the LDL particle. Simulation of the small angle X-ray scattering curves and comparison with published data suggested that this disrupted shell organization represents an intermediate state in the transition from isotropic to layered packing of the lipid. Thus, the results revealed, with 3D images, the lipid packing in the dynamic process of the LDL lipid-core phase transition.

Reversible structural phase transition and dielectric behaviour associated with the ordering-disordering of molecular rotation in an organic supramolecular solid

GeTe Thermoelectrics

Simultaneous control of the magnetic and electric properties of materials is crucial for their application in next-generation memory and sensor devices. Herein, we report a single-crystal Co(II) co...

The structures and dielectric properties of high temperature phase transition compounds with 4-(dimethylamino)pyridinium

Organic-inorganic silver halide hybrids show abundant phase transitions and thermochromism. However, it is very rare that silver halides exhibit thermochromism related to thermotropic structure phase transition. Herein, a bromoargentate hybrid, [Pr-dabco]2Ag4Br6 (1) (Pr-dabco+ = 1-propyl-1,4-diazabicyclo-[2.2.2]octan-1-ium), with tetranuclear [Ag4Br6]2- clusters was prepared and characterized by microanalysis, ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, and thermogravimetric (TG) and differential scanning calorimetry (DSC) techniques. Interestingly, 1 undergoes an irreversible structure phase transition at ∼436 K in the first heating process, which is accompanied by an abrupt color change from colorless to yellow; however, a reversible color change between pale yellow and yellow is observed in the next heating-cooling cycles. Notably, DSC measurement revealed that a reversible phase transition is associated with the change in color between pale yellow and yellow, while the powder X-ray diffraction (PXRD) patterns corresponding to pale yellow and yellow phases are quite similar to each other. These observations demonstrate that thermochromism in the next heating-cooling runs is associated with a reversible structure phase transition, which perhaps concerns the disorder-order transformation of alkyl chains in the cationic ligand [Pr-dabco]+, and relevant to the anharmonic fluctuations of the Ag-Br and Ag-N bonds, a strong electron-phonon coupling effect is seen within the bromoargentate cluster.

The interaction of four long-chain nicotinates, compounds that are of interest as potential chemopreventive agents, with dipalmitoylphosphatidylcholine (DPPC) was investigated in monolayers at the air-water interface and in fully hydrated bilayers. For the monolayer studies, the compression isotherms of mixtures of the respective nicotinate with DPPC were recorded at various compositions on a hydrochloric acid subphase (pH 1.9-2.1, 37 +/- 2 degrees C). The headgroup of the nicotinates (24-29 A2/molecule) is larger than that of the hydrophobic tail (20 A2/molecule). The pure nicotinates exhibit a temperature- and chain length-dependent transition from an expanded to a condensed phase. Analysis of the concentration dependence of the average molecular area at constant film pressure and the concentration dependence of the breakpoint of the phase transition from the expanded to the condensed state suggests that all four DPPC-nicotinate mixtures are partially miscible at the air-water interface. Although a complex phase behavior with several phase transitions was observed, differential scanning calorimetry studies of the four mixtures are also indicative of the partial miscibility of DPPC and the respective nicotinate. Overall, the complex phase behavior most likely results from the head-tail mismatch of the nicotinates and the geometric packing constraints in the two-component lipid bilayer.

Dynamic molecular materials, which involve mechanical motions in crystals, usually exhibit tunable properties related to conformational polymorphs. Herein, we describe a solvent-free molecular crys...

Heating-Induced Phase Transition of Bupropion Hydrobromide Polymorphs

Thermoelectric materials with crystal-amorphicity duality induced by large atomic size mismatch

Organic-inorganic hybrid materials with perovskite structure have recently attracted tremendous interest due to their structural tunability and rich functional properties, such as phase transition and photoelectric properties. Within this context, two discrete tin-based organic-inorganic hybrid compounds [(FMBA)2SnCl6] (1) and [(FMBA)2SnBr6] (2) were prepared by the reaction of 3-fluoro-N-methylbenzylamine (FMBA) with SnX4 (X = Cl, Br) in the corresponding concentrated halogen acids HX. Differential scanning calorimetry (DSC) and dielectric measurements showed that both compounds underwent reversible phase transition and dielectric anomaly at a phase transition point above 400 K. Crystal structure analyses revealed that the phase transition mainly originated from the order and disorder of a fluorine-substituted organic amine structure at low and high temperatures. Meanwhile, both compounds showed a semiconducting property with optical bandgaps of 4.24 eV for 1 and 2.58 eV for 2. This finding of two Sn(iv)-based metal halides with prominent phase transition and semiconducting behaviors will expand an executable pathway for designing multifunctional perovskite-type switchable materials.

An organic-inorganic hybrid molecule [3.3.0-H2dabco]ZnBr4 (1) with switchable phase transition, dielectric anomaly, and second harmonic generation (SHG) effect was synthesized by reaction of 1,5-diazabicyclo[3.3.0]octane (3.3.0-dabco) with ZnBr2 in concentrated hydrobromic acid aqueous solution. Differential scanning calorimetry (DSC) and dielectric measurements revealed that 1 exhibits a reversible high-temperature phase transition, accompanied by a distinct step-like dielectric anomaly at 373 K. Exceptionally, the single crystal structure analysis at different temperatures revealed that 1 undergoes reverse symmetry breaking during the phase transition, in which the high-symmetry space group Cc in the low temperature phase (LTP) is transformed to the low-symmetry space group P1̅ in the high temperature phase (HTP). In addition, with the conversion from the non-centrosymmetric (NCS) to the centrosymmetric (CS) space group, the SHG of 1 can switch from SHG-ON to SHG-OFF for at least four cycles without obvious decay.