[(18-Crown-6)K][Fe(1)Cl(1)4 ]0.5 [Fe(2)Cl(2)4 ]0.5 : A Multifunctional Molecular Switch of Dielectric, Conductivity and Magnetic Properties

Supramolecular crystals of Mn(15-crown-5)(MnCl4)(DMF) with dielectric phase transition, high quantum yield and phase transition-induced luminescence enhancement behavior

The supramolecular crystals, Mn(15-crown-5)(MnCl4)(DMF), (1; 15-crown-5 = 1,4,7,10,13-pentaoxacyclopentadecane), were synthesized via a self-assembly strategy under ambient conditions. Comprehensive characterization of the crystals involved microanalysis for C, H, and N elements, thermogravimetric (TG) analysis, differential scanning calorimetry (DSC) and single-crystal X-ray diffraction techniques. The results reveal that 1 undergoes a two-step thermotropic and isostructural phase transition at around 217 K and 351 K upon heating. All three phases belong to the same space group (P212121) with analogous cell parameters. These two phase transitions primarily involve the thermally activated ring rotational dynamics of the 15-crown-5 molecule, with only the transition at ca. 351 K being associated with a dielectric anomaly. 1 exhibits intense luminescence with a peak at ∼600 nm and a high quantum yield of 68%. The mechanisms underlying this intense luminescence are likely linked to low-symmetry ligand fields. Additionally, 1 displays phase transition-induced luminescence enhancement behavior, and the possible mechanism is further discussed.

2-Chloroethylamine·trifluoromethanesulfonate combined with 18-crown-6: a ferroelectric with excellent dielectric switching properties

Ferroelectric materials are not only important electronic functional materials, but also considered as the most promising intelligent basic materials, because they show good application prospects. Therefore, it is an urgent task to develop and explore new ferroelectric material systems. In addition, the most important feature of crown ethers is their ability to complex with positive ions, which is extremely useful in synthesis. We report that [NH3C2H4Cl(18-crown-6)](CF3SO3) (1) has a phase transition temperature Tc = 255 K, and there is an obvious SHG switch below Tc. At the same time, the saturation polarization value Ps = 1.25 μC cm-2 is obtained from the hysteresis loop, which directly proves the ferroelectric nature of compound 1. It is noteworthy that the second harmonic response test of compound 1 shows a symmetric transition from a non-centrosymmetric to a centrosymmetric point group, that is a symmetry break from the paraelectric phase to the ferroelectric phase. This work is expected to promote the further exploration of organic crown ether ferroelectrics and provide a way to design and synthesize organic crown ether ferroelectrics.

Dielectric Relaxation and Beyond Limiting Behavior of Alternating-Current Conductivity in a Supermolecular Ferroelectric

A cyclen-based hybrid supermolecule crystal, [(FeCl₂ )(cyclen)]Cl (1), where cyclen=1,4,7,10-tetraazacyclododecane, was prepared using a liquid-liquid diffusion approach. The variable crystal structures exhibit that compound 1 belongs to an orthorhombic crystal system, Pna2₁ space group (point group C_2V ) in the temperature range of 150-400 K. This hybrid supermolecule shows a dielectric relaxation behavior around room temperature, and the ferroelectric nature of 1 has been directly verified by hysteresis measurements. In addition, the AC (alternating current) conductivity study reveals that the 1 displays a beyond limiting behavior. These interesting findings are for the first time reported in the field of supermolecular ferroelectrics. This study may open a new way to construct supermolecular ferroelectrics and give insights into their conductor behavior.

An organometallic half-sandwich supramolecular complex {K(18-Crown-6)(ηn-C6H5B(C6H5)3)} (n = 1–6) exhibiting a reversible breaking-symmetry phase transition and switchable dielectric behaviour

An organometallic supramolecular crystal of {K(18-crown-6)(ηⁿ-C₆H₅B(C₆H₅)₃)} (n = 1–6) has a half-sandwich structure and exhibits a reversible breaking-symmetry phase transition and switchable dielectric behavior.