Twonewhigh-temperaturemolecularferroelectrics[1,5-3.2.2-Hdabcn]X（X=ClO4-,ReO4-）

Molecular ferroelectrics have attracted much attention because of their excellent piezoelectricity, mechanical workability, and second harmonic effect. Here, we successfully prepared two molecular ferroelectrics [1,5–3.2.2-Hdabcn]X（X = ClO4-, 1; ReO4-, 2） by reactions of a quasi-spherical amine 1,5-diazabicycle[3.2.2]nonane（1.5–3.2.2-dabcn） with HX aqueous solution. Compounds 1 and 2 undergo hightemperature phase transitions at 381 K（1） and 396 K（2）. Before and after the phase transition, they crystallize in the polar point group mm2, and the centrosymmetric point groups mmm and 4/mmm, respectively. According to Aizu rules, these two compounds experience mmm Fmm2 and 4/mmm Fmm2 type ferroelectric phase transitions, respectively. The ferroelectricity of both compounds is well expressed in their polycrystalline film at room temperature with low coercive voltages of 13 V for 1 and 25 V for 2. Using piezoelectric force microscopy（PFM）, the 180° anti-parallel ferroelectric domains and the reversible polarization switching can be clearly observed in 1 and 2. This high-temperature molecular ferroelectric material has great application potential in flexible materials, biomechanics, intelligent wearables and other fields.