Following the Curie symmetry principle and Aizu rule, we discovered there is a centrosymmetric-to-noncentrosymmetric phase transition in Ca(NO₃)₂(15-crown-5) at T_c=205 K. The transition was confirmed by differential scanning calorimetry and second harmonic generation measurements. The transition gives rise to excellent ferroelectricity, such as a giant dielectric anomaly, with faster polarization switching (5×10⁻⁵ s) of up to 10⁷ times without showing fatigue. The ferroelectric mechanism is attributable to the coordination environmental distortion of the central Ca atom. This finding can throw light on the further research in metal–organic ferroelectrics.

The host–guest complex [(DIPA)([18]crown-6)](ClO₄) (1; DIPA=2,6-diisopropylanilinium) was constructed and found to undergo a sequence of phase transitions (Ibam–Pbcn–Pna2₁) at T₁=278 K and T₂=132 K, respectively. Systematic characterizations, such as differential scanning calorimetry, heat capacity, temperature-dependent dielectric constant, and P–E hysteresis loop, reveal that the centrosymmetric-to-polar phase transition at T₂ is a paraelectric-to-ferroelectric transition. The symmetry breaking was also confirmed by temperature-dependent second-harmonic generation effect and X-ray powder diffraction. The ferroelectric mechanism is attributable to the linear motion of the perchlorate counterions accompanied by the order–disorder transition of the [18]crown-6 molecules and the anions.

Molecular ferroelectric thin films are highly desirable for their easy and environmentally friendly processing, light weight, and mechanical flexibility. A thin film of imidazolium perchlorate processed from aqueous solution is an excellent molecular ferroelectric with high spontaneous polarization, high Curie temperature, low coercivity, and superior electromechanical coupling. These attributes make it a molecular alternative to perovskite ferroelectric films in sensing, actuation, data storage, electro-optics, and molecular/flexible electronics.

Following the Curie symmetry principle and Aizu rule, we discovered there is a centrosymmetric-to-noncentrosymmetric phase transition in Ca(NO₃)₂(15-crown-5) at T_c=205 K. The transition was confirmed by differential scanning calorimetry and second harmonic generation measurements. The transition gives rise to excellent ferroelectricity, such as a giant dielectric anomaly, with faster polarization switching (5×10⁻⁵ s) of up to 10⁷ times without showing fatigue. The ferroelectric mechanism is attributable to the coordination environmental distortion of the central Ca atom. This finding can throw light on the further research in metal–organic ferroelectrics.

Hybrid organo–metal halide perovskite materials, such as CH₃NH₃PbI₃, have been shown to be some of the most competitive candidates for absorber materials in photovoltaic (PV) applications. However, their potential has not been completely developed, because a photovoltaic effect with an anomalously large voltage can be achieved only in a ferroelectric phase, while these materials are probably ferroelectric only at temperatures below 180 K. A new hexagonal stacking perovskite-type complex (3-pyrrolinium)(CdCl₃) exhibits above-room-temperature ferroelectricity with a Curie temperature T_c=316 K and a spontaneous polarization P_s=5.1 μC cm⁻². The material also exhibits antiparallel 180° domains which are related to the anomalous photovoltaic effect. The open-circuit photovoltage for a 1 mm-thick bulky crystal reaches 32 V. This finding could provide a new approach to develop solar cells based on organo–metal halide perovskites in photovoltaic research.

The host–guest complex [(DIPA)([18]crown-6)](ClO₄) (1; DIPA=2,6-diisopropylanilinium) was constructed and found to undergo a sequence of phase transitions (Ibam–Pbcn–Pna2₁) at T₁=278 K and T₂=132 K, respectively. Systematic characterizations, such as differential scanning calorimetry, heat capacity, temperature-dependent dielectric constant, and P–E hysteresis loop, reveal that the centrosymmetric-to-polar phase transition at T₂ is a paraelectric-to-ferroelectric transition. The symmetry breaking was also confirmed by temperature-dependent second-harmonic generation effect and X-ray powder diffraction. The ferroelectric mechanism is attributable to the linear motion of the perchlorate counterions accompanied by the order–disorder transition of the [18]crown-6 molecules and the anions.

Hybrid organo–metal halide perovskite materials, such as CH₃NH₃PbI₃, have been shown to be some of the most competitive candidates for absorber materials in photovoltaic (PV) applications. However, their potential has not been completely developed, because a photovoltaic effect with an anomalously large voltage can be achieved only in a ferroelectric phase, while these materials are probably ferroelectric only at temperatures below 180 K. A new hexagonal stacking perovskite-type complex (3-pyrrolinium)(CdCl₃) exhibits above-room-temperature ferroelectricity with a Curie temperature T_c=316 K and a spontaneous polarization P_s=5.1 μC cm⁻². The material also exhibits antiparallel 180° domains which are related to the anomalous photovoltaic effect. The open-circuit photovoltage for a 1 mm-thick bulky crystal reaches 32 V. This finding could provide a new approach to develop solar cells based on organo–metal halide perovskites in photovoltaic research.

The title ammonium compound ethyl 2-(4-aminophenoxy)acetate (C₁₀H₁₃NO₃, I) and its crown ether inclusion complex {[(C₁₀H₁₄NO₃)·(18-crown-6)]⁺[PF₆]⁻, II} (18-crown-6=1,4,7,10,13,16-hexaoxacyclo-octadecane) were synthesized. The ammonium compound I was determined by ¹H NMR, IR and ESI-MS techiniques. X-ray crystallography reveals that compound I crystallizes in the triclinic system with space group of P-1, all the atoms in I are almost coplanar except H, and NH···O hydrogen bonds lead to the formation of one dimensional chain. The rotator-stator-like compound II was crystallizes in the centrosymmetric monoclinic system with space group of P21/c. The supramolecular was formed via NH···O hydrogen-bond interactions. Temperature-dependent dielectric constants of compound II were measured.

The molten reaction of 2-naphthol, 2-hydroxybenzaldehyde and tetrahydropyrrole at about 120°C yields 1-[(2-hydroxyphenyl)(pyrrolidin-1-yl)-methyl]naphthalen-2-ol, whose co-crystal (1) with 2-naphthol was characterized by X-ray single crystal diffraction, XRPD and IR. Compound 1 crystallizes in a noncentrosymmetric space group (Fdd2) with unit cell dimensions of a=2.9395(9) nm, b=3.468(3) nm, c=0.8013(8) nm, V=8.170(13) nm³, α=β=γ=90.0° and Z=8 [at 293(2) K]. The piezoelectric measurement result shows compound 1 is piezoelectrically active material with d₃₃ value of ca. 6.2 pC/N. Temperature- and frequency-dependent dielectric constant of compound 1 were measured and showed no distinct dielectric anomaly, which suggest no phase transition within the measured temperature range (100–410 K).

The thermal treatment of CuCl₂ with N-(4′-vinylbenzyl)cinchonidinium chloride (L1) afforded a monomeric discrete homochiral copper(II) complex N-4′-(vinylbenzyl)cinchonidinium trichlorocoprate(II) (1). Their applications to the enantioselectively catalytic alkylation reaction of N-(diphenylmethylidene)glycine tert-butyl ester (3) show that the higher ee value observed in catalyst 1 than that in the corresponding free ligand L1 is probably due to the rigidity enhancement after the coordination of N atom of quinoline ring to the copper ion.

Colorless block crystals of MOF (metal-organic framework) 1 and 2 were prepared in respective yields of 65 and 60 % by thermal treatment of HQA (HQA=6-methoxyl-(8S,9R)-cinchonan-9-ol-3-carboxylic acid) with ZnBr₂ in either H₂O or D₂O and 2-butanol at 70 °C for 1–2 days. The MOFs 1 and 2 are isostructural, one-dimensional chains in which the local coordination geometry around the Zn center can be best described as a slightly distorted tetrahedron defined by two bromine atoms, one nitrogen atom of quinoline from HQA, and an oxygen atom of carboxylate from HQA. The nitrogen atom of the quinuclidine of HQA is protonated in a zwitterionic form. The MOFs 1 and 2 crystallize in a polar point group (C₂, space group P2₁) which belongs to ferroelectric active compounds. MOFs 1 and 2 display both ferroelectric behavior and large dielectric constants. Interestingly, at low frequency range the dielectric response to water can achieve an approximate increase of more than 600 %. Crystal parameters: 1: C₂₀H₂₈Br₂NO₇Zn, M=619.62, monoclinic, P2₁, a=9.5711(8), b=12.0486(10), c=11.1972(9) Å, α=γ=90, β=98.4(2)°, V=1277.39(18) ų, Z=2, ρ_cald=1.611 mg m⁻³, R₁=0.0499, wR₂=0.0982, μ=4.126 mm⁻¹, S=1.015, Flack value=0.032(13); 2: C₂₀H₂₂D₆Br₂NO₇Zn, M=625.66, monoclinic, P2₁, a=9.5650(9), b=12.0392(11), c=11.1973(10) Å, α=γ=90, β=98.44(2)°, V=1275.5(2) ų, Z=2, ρ_cald=1.629 mg m⁻³, R₁=0.0543, wR₂=0.1072, μ=4.133 mm⁻¹, S=1.056, Flack value=0.025(17).

Hydrothermal (deuteratothermal) reaction of L-ethyl lactate (Lig-Et) with Eu(ClO₄)₃⋅6 H₂O gives colorless block crystals of [Eu(Lig)₂(X₂O)₂][ClO₄] (1, X=H; 2, X=D) both of which possess a two-dimensional laminar homochiral framework. Single-crystal dielectric measurements reveal that 1 and 2 display a giant dielectric anisotropy approximately exceeding 100 and large isotopic effect with about 54 % enhancement along the a axis. Their ferroelectric features further confirm this respect. Crystal parameters: 1, C₆H₁₄ClO₁₂Eu, M_r=465.58, monoclinic, C₂, a=8.6786(6), b=8.3965(6), c=10.2153(7) Å, β=92.040(1)°, V=743.92(9) ų, Z=2, ρ_calcd=2.079 Mg m⁻³, R₁=0.0508, wR₂=0.1239, μ=4.448 mm⁻¹, S=1.043; Flack=0.04(5). 2: C₆H₁₀D₄ClO₁₂Eu, M_r=469.61, monoclinic, C₂, a=8.689(2), b=8.410(2), c=10.224(3) Å, β=92.057(4)°, V=746.7(3) ų, Z=2, ρ_calcd=2.089 Mg m⁻³, R₁=0.0465, wR₂=0.1150, μ=4.432 mm⁻¹, S=1.058; Flack=0.02(5).