Designing and Constructing a High‐Temperature Molecular Ferroelectric by Anion and Cation Replacement in a Simple Crown Ether Clathrate

Abstract Molecular ferroelectrics have displayed a promising future since they are light‐weight, flexible, environmentally friendly and easily synthesized, compared to traditional inorganic ferroelectrics. However, how to precisely design a molecular ferroelectric from a non‐ferroelectric phase transition molecular system is still a great challenge. Here we designed and constructed a molecular ferroelectric by double regulation of the anion and cation in a simple crown ether clathrate, 4 , [K(18‐crown‐6)] + [PF 6 ] − . By replacing K + and PF 6 − with H 3 O + and [FeCl 4 ] − respectively, we obtained a new molecular ferroelectric [H 3 O(18‐crown‐6)] + [FeCl 4 ] − , 1 . Compound 1 undergoes a para ‐ferroelectric phase transition near 350 K with symmetry change from P 21/ n to the Pmc 21 space group. X‐ray single‐crystal diffraction analysis suggests that the phase transition was mainly triggered by the displacement motion of H 3 O + and [FeCl 4 ] − ions and twist motion of 18‐crown‐6 molecule. Strikingly, compound 1 shows high a Curie temperature (350 K), ultra‐strong second harmonic generation signals (nearly 8 times of KDP), remarkable dielectric switching effect and large spontaneous polarization. We believe that this research will pave the way to design and build high‐quality molecular ferroelectrics as well as their application in smart materials.