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Three-dimensional (3D) hybrid organic–inorganic perovskites (HOIPs) have attracted tremendous research interest due to their unique structure and promising applications. However, research on the design, synthesis and properties of this kind of metal-free crystalline material is still in the exploratory stage. Herein, two 3D perovskite molecules [1,4-3.2.2-dabcn]NH4Br3 (1) and [1,4-3.2.2-dabcn]NH4I3·0.5H2O (2) were obtained by reacting 1,4-diazabicyclo[3.2.2]nonane (1,4-3.2.2-dabcn) with NH4X (X = Br and I) in the corresponding concentrated halogen acids. The single X-ray diffraction results demonstrated that the inorganic framework structures in compounds 1 and 2 constructed with NH4Br and NH4I are completely different, caused by the radius of the bromide ion being smaller than that of the iodide ion. The 3D framework of compound 1 is constructed with a coplanar dimer [(NH4)2Br6]2− as the basic building unit, leading to the expanded 3D perovskite framework structure with a larger cavity to accommodate the 1,4-3.2.2-dabcn molecule. Nevertheless, compound 2 adopts a familiar 3D crystal framework structure with corner-sharing [(NH4)I6] octahedra, where the [1,4-3.2.2-dabcn] cations and water solvent molecule are confined in the cavities enclosed by the octahedra. Notably, both compounds exhibit reversible phase transition, dielectric anomaly and the second harmonic generation (SHG) effect. From the perspective of molecular design, this work is of great significance to guide the construction of new 3D metal-free perovskite molecular materials with reversible properties. [ABSTRACT FROM AUTHOR]

Although organic molecule phase transition materials (OMPTM) have been studied by many scholars owing to their light weight and easy processing, single-component OMPTM with two reversible phase transitions have rarely been reported. Herein, we report an organic inner salt, 1-sulfo-4-dimethylamino-pyridinium (1), which exhibits two phase transitions at 286 K and 311 K, accompanied by obvious dielectric anomalies. Moreover, the variable-temperature single X-ray crystal structure analysis revealed that 1 undergoes an order–disorder symmetry breaking from 243 K (phase I) to 293 K (phase II), in which the centrosymmetric space group P21/n is transformed into the space group of Pnma. However, from phase II to phase III, there is no space group change, and 1 proceeds with an isostructural phase transition. Overall, this study highlights the exploration of the phase transition mechanism of single-component OMPTM. [ABSTRACT FROM AUTHOR]

The emergence of (CH3NH3)PbI3 has brought the development of three‐dimensional (3D) organic‐inorganic hybrid perovskite (OIHP) structures with ABX3 type to a higher level; however, most 3D frameworks are constructed by corner‐sharing of BX6 octahedra. Herein, we substituted the spherical molecule 1,4‐diazabicyclo[2.2.2]octane (2.2.2‐dabco) with 1,4‐diazabicyclo[3.2.2]nonane (1,4‐3.2.2‐dabcn) as a template to react with RbX (X=Br, I) in the corresponding HX acids under the consideration of reducing the molecular symmetry. Two 3D OIHP compounds [1,4‐3.2.2‐H2dabcn]RbI3⋅H2O (1) and [1,4‐3.2.2‐H2dabcn]RbBr3 (2) crystallized in non‐centrosymmetric point group mm2 before the phase transition point were isolated. Among them, the 3D inorganic framework of 1 is constructed by sharing the corner of [RbI6] octahedra, while that of 2 is constructed by sharing the corner and face of [RbBr6] octahedra to acquire large cavities to accommodate the organic amine cation [1,4‐3.2.2‐H2dabcn]2+; this 3D framework type is unprecedented in the OIHPs. As expected, compounds 1 and 2 exhibit reversible phase transition, dielectric and second harmonic generation (SHG) and ferroelectric properties, in which the phase transition temperature of 2 at 374 K is much higher than compound 1 at 280 K. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid perovskites are categorized as multifunctional materials due to their structural designability and functional diversity. Herein, two manganese-based organic–inorganic perovskite type compounds [Me3NNH2]MnCl3 (1) and [(CH3)3NCH2CH2F]2MnCl4 (2) were synthesized by reactions of trimethylhydrazine iodide and (fluoromethyl)trimethylammonium bromide with MnCl2 in concentrated hydrochloric acid aqueous solution. Differential scanning calorimetry (DSC) and dielectric measurements revealed that compounds 1 and 2 undergo reversible phase transitions at about 327 K and 352 K, respectively. Significantly, under the excitation of 365 nm, compounds 1 and 2 emit green and red luminescence, which originate from the octahedral [MnCl6] and tetrahedral [MnCl4] moieties. [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]

A one-dimensional organic–inorganic hybrid perovskite material [3.3.0-dabco]PbBr3 (1) was synthesized by the reaction of 1,5-diazabicyclo[3.3.0]octane (3.3.0-dabco) with PbBr2 in concentrated HBr aqueous solution. Differential scanning calorimetry, dielectric measurements, and variable-temperature structural analyses revealed that compound 1 exhibits two successive structural phase transitions from P212121 to Pbcm at 387 K (T1) and then to P6/mmc at 436 K (T2), accompanied by two pairs of dielectric anomalies with a clear one at T1 and an unobvious one at T2. In addition, compound 1 shows a robust second harmonic generation (SHG) effect between SHG-OFF and SHG-ON states during its centrosymmetric to non-centrosymmetric symmetry breaking phase transition at T1. [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]

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. [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]

• Synthesis two lead-free halides [3-FPEA] 3 (SbCl 4)Cl 2 and [3-FPEA] 4 (BiI 6)I. • Both hybrid perovskites have reversible phase transitions. • Both materials are lead-free semiconductor materials. Metal halide organic-inorganic hybrid perovskite is a kind of rapid development of semiconductors but its major development has been concentrated in lead-based perovskites. Here we report two zero-dimensional non-lead halide perovskites [3-FPEA] 3 (SbCl 4)Cl 2 (1) and [3-FPEA] 4 (BiI 6)I (2) (3-FPEA = 3-fluorophenethylamine) with the reversible phase transitions. The differential scanning calorimetry (DSC) and UV-vis absorption measurements of 1 and 2 revealed that the phase transition temperatures are 350 K (1) and 335 K (2), the bandgaps are 3.53 eV (1) and 2.14 eV (2), respectively. The room temperature X-ray single crystal diffraction showed the cation [3-FPEA]+ in 1 and 2 proceeds a twofold disorder, and the anions in 1 are a dimer [Sb 2 Cl 10 ] constructed with [SbCl 6 ] octahedra by sharing the Cl···Cl edge, and the anions in 2 are the discrete [BiI 6 ] octahedron. This study can provide an effective molecular design strategy for exploring and investigating non-lead-based halide perovskite semiconductive phase change materials. [Display omitted] [ABSTRACT FROM AUTHOR]

A discrete organic-inorganic hybrid compound [(3.2.1-dabco) 2 PbBr 6 exhibited a reversible phase transition which was originated from the order to disorder of spherical [3.2.1-dabco]2+ cation at RTP and HTP. • A spherical molecule 1, 5-diazabicyclo[3,2,1]octane was chose to react with PbBr 2 to give an organic-inorganic compound. • The obtained hybrid compound showed a reversible phase transition. • The variable temperature X-ray single crystal diffraction revealed the phase transition was derived from the order and disorder of spherical molecule at room temperature and high temperature. Organic-inorganic hybrid materials were attracted most interests due to their potential applications in phase transition and photoelectric fields. Within this context, a spherical molecule 1, 5-diazabicyclo[3,2,1]octane (3,2,1-dabco) was used to react with PbBr 2 in concentrated HBr acid and led to a discrete organic inorganic hybrid compound [(3,2,1-dabco) 2 PbBr 6 (1). Thermodynamic DSC analyses and dielectric measurement of 1 showed an apparently reversible phase transition at about 427 K. The variable temperature X-ray single crystal diffraction demonstrated compound 1 underwent an order-disorder transition from orthorhombic to cubic systems at room and high temperatures. [ABSTRACT FROM AUTHOR]

Abstract Reactions of 3-fluoro-N-methylbenzylamine (FBMA) with PbBr 2 in concentrated HBr aqueous solution afforded a two-dimensional (2D) single layered organic-inorganic hybrid material [(FBMA) 2 PbBr 4 ], which was confirmed by X-ray single crystal diffraction, infrared (IR) spectroscopy and powder X-ray diffraction (PXRD). The thermodynamic DSC analysis revealed it has a pair of reversible phase transition peaks with large thermal hysteresis exhibiting a first-order type phase transition. The variable-temperature single crystal diffraction proved the phase transition is originated from the order and disorder of organic-inorganic hybrid structures at room and high temperatures. Simultaneously compound [(FBMA) 2 PbBr 4 ] exhibited a strong emission peak at 443 nm when under an excitation wavelength of 380 nm. Graphic abstract A new two-dimensional (2D) single layered organic-inorganic hybrid material (FC 6 H 4 CH 2 NH 2 CH 3) 2 [PbBr 4 ] showed a first-order type phase transition, which was originated from the order-disorder transition of organic-inorganic hybrid structures at room and high temperatures. fx1 Highlights • A new layered organic-inorganic-hybrid perovskite is designed, synthesized, and characterized. • The relationship between phase transitions and structural changes is addressed. • The optical property of (FC 6 H 4 CH 2 NH 2 CH 3) 2 [PbBr 4 ] is studied. [ABSTRACT FROM AUTHOR]