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The excellent properties of host–guest crown ether inclusions in phase transition, dielectric and second-order nonlinear optical properties have attracted much attention. In this paper, we successfully designed and prepared two novel host–guest crown ether supramolecules [(DFBA)(15-crown-5)]X (X = ClO4−, 1; ReO4−, 2) by reactions of 2,6-difluorobenzylamine (DFBA) with 1,4,10,13-pentaoxacyclopentadecane (15-crown-5) in HClO4, or HReO4 aqueous solution. By the introduction of difluoro-substituted benzylamine as a guest cation, the phase transition temperatures are greatly increased to 377 K for 1 and 391 K for 2. More importantly, the space group of 1 has changed from centrosymmetric (CS) P2/c to the non-centrosymmetric (NCS) Pca21 in 2 when substituting perchlorate (ClO4−) with the larger and heavier perrhenate (ReO4−), which leads to 2 showing a switchable and stable second-harmonic generation (SHG) effect. According to the principle of momentum matching between a cation and anion, the perrhenate group increases the energy barrier of the molecular thermal motion, which not only significantly increases the phase transition temperature of 2 but also causes it to be frozen and crystallized in a NCS space group at room temperature. This research demonstrates that a polar molecule can adjust the suitability of anions and cations inside the crystal by practical chemical means. [ABSTRACT FROM AUTHOR]

Often, the quasi-spherical molecule 1,4-diazabicyclo[2.2.2]octane (2.2.2-dabco) is chosen to prepare switchable materials with a high phase transition temperature. We wished to reduce molecular symmetry but maintain a quasi-spherical shape. Hence, a similar molecule, 1,4-diazabicyclo[3.2.2]nonane (3.2.2-dabcn), was used to react with equimolar amounts of HClO4 or HReO4 in aqueous solution. Two compounds [3.2.2-Hdabcn]X (X = ClO4, 1; ReO4, 2) with high phase-transition points at 418 K for 1 and 394.6 K and 419.2 K for 2, respectively, were isolated, in which one-dimensional cationic chains were connected by different types of hydrogen bonds. Differential scanning calorimetry and dielectric-permittivity measurements revealed that 1 and 2 showed switchable phase transition and dielectric anomalies. Compound 1 also showed a reversible second-harmonic-generation effect. [ABSTRACT FROM AUTHOR]

Recently, hybrid organic‐inorganic lead halide materials have attracted great attention for their applications in the fields of light‐emitting diodes, photovoltaics, photodetector. However, these hybrid materials usually suffer from environmental and human health issues because of the toxic lead moieties. Herein, we report a novel lead‐free bismuth iodide phase transition material, [NH3(CH2)7NH3][BiI5] (1), which undergoes a reversible phase transition at high temperature 351.7 K and exhibits a step fashion dielectric anomaly. The structural phase transition of 1 is mainly originated from the order‐disorder transition of the 1,7‐heptanediamine cations. Besides, the solid‐state UV‐vis spectrum of 1 displays an intense adsorption at around 658 nm; which gives an indirect bandgap of 1.89 eV. Such a small bandgap value is comparable to most of the organic‐inorganic hybrid lead halide type semiconductors. We believe this study will shed light on the exploration of lead‐free organic‐inorganic hybrid metal halide semiconductors toward future device applications. [ABSTRACT FROM AUTHOR]

Recently, the development of multifunctional thermochromic materials that exhibit switching characteristics in phase transition and dielectric properties has attracted widespread attention due to their potential application in signal processing and smart devices. But most traditional thermochromic materials tend to be rather than reversible phase change materials. Here, a square-pyramidal coordinated copper complex [Me3NNH2CuCl3]2 (1) (Me3NNH2 = trimethyl hydrazine) showing switchable properties in phase transition, dielectricity and thermochromic properties has been prepared by reaction of Me3NNH2I with CuCl2 in concentrated HCl aqueous solution. Compound 1 has a reversible phase transition temperature of 45 °C. When the temperature exceeds the phase transition temperature, the green color of 1 gradually changed into dark red. Compared with traditional thermochromic materials, the reversible phase transition and dielectric properties within the thermochromic materials will bring additional spectral encryption possibilities for future information processing. [ABSTRACT FROM AUTHOR]

An octahedral coordinated nickel(II) hydrazinium complex was prepared by reaction of NiCl 2 with trimethyl hydrazinium showing reversible phase transition, dielectric anomaly and thermochromism. [Display omitted] • A nickel complex based on hydrazinium exhibits switchable thermochromic properties. • The nickel complex also shows reversible dielectric property and phase change. • The mechanism of thermochromism was explained by single crystal X-ray diffraction. Thermochromism in copper complexes is known, but nickel thermochromic complex materials are less reported. Herein, we synthesized a nickel metal complex [(Me 3 NNH 2) 2 NiCl 4 ] (1) based on 1,1,1-trimethylhydrazinium iodide and nickel chloride, which exhibited excellent switching properties in terms of dielectric and phase change and thermochromic properties from yellow to blue. Compound 1 was subjected to the variable temperature single crystal X-ray diffraction, and it was found that the crystal space group did not change after the temperature exceeded the phase transition point, so the thermochromism may be caused by the structural phase transition of the compound. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) organic-inorganic hybrid perovskite (OIHP) has the advantages of excellent material stability, structural diversity and ease of manufacturability. It is worth noting that the fluorination strategy has been recognized as a convenient molecular design method that can effectively customize and optimize physical and chemical properties in 2D OIHP materials. However, selection the fluorine-chlorine double substituted organic amine to construct lead halide OIHP molecules was not reported. Here, for the first time, we successfully obtained a 2D metal halide perovskite compound [4-Cl-2-FBA] 2 PbBr 4 (1) by reactions of lead bromide with two equivalents of 4-chloro-2-fluorobenzylamine [4-Cl-2-FBA] in concentrated HBr aqueous solution. Its crystal structure and purity were confirmed by X-ray single crystal diffraction and powder X-ray diffraction (PXRD). Differential scanning calorimetry (DSC) and dielectric measurement analyses showed the phase transition (PT) temperature of 1 is 380.1 ​K which is higher than that of [2-FBA] 2 PbBr 4 , (2-FBA ​= ​2-fluorobenzylammonium, 364 ​K), but lower than those of (benzylammonium) 2 PbBr 4 (405 ​K) and [PFBA] 2 PbBr 4 (PFBA ​= ​perfluorobenzylammonium, 440 ​K). A two-dimensional (2D) organic-inorganic hybrid perovskite material [4-Cl-2-FBA] 2 PbBr 4 (1) with high phase transition temperature and semiconductive property was isolated by reactions of lead bromide with two equivalents of 4-chloro-2-fluorobenzylamine [4-Cl-2-FBA] in concentrated HBr aqueous solution. [Display omitted] • A fluorine and chlorine substituted 2D metal halide perovskite was firstly prepared by reactions of PbBr 2 ​with 4-chloro-2-fluorobenzylamine. • DSC analysis showed the phase transition temperature of ​ 1 ​is 380.1 K which is higher than that of [2-FBA] 2 PbBr 4 ​at 364 K. • The 2D metal halide perovskite was characterized by the variable temperature X-ray single crystal diffraction. [ABSTRACT FROM AUTHOR]