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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]

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]

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]

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]

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]