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

• Published in: Chemistry, an Asian journal Vol. 14; no. 21; pp. 3946 - 3952
• Main Authors: Zhou, Hai‐Tao, Wang, Chang‐Feng, Liu, Yao, Fan, Xiao‐Wei, Yang, Kang, Wei, Wen‐Juan, Tang, Yun‐Zhi, Tan, Yu‐Hui
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 04.11.2019
• Subjects: Anions; Cations; chemical design; Chemistry; Clathrates; crown ether clathrate; Crown ethers; Curie temperature; Dielectric strength; Ferroelectric materials; Ferroelectricity; Ferroelectrics; large spontaneous polarization; molecular ferroelectrics; Phase transitions; Second harmonic generation; Signal generation; Smart materials; Weight reduction; molecular ferroelectrics; crown ether clathrate; second harmonic generation; chemical design; large spontaneous polarization
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201901265

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)]+[PF6]−. By replacing K+ and PF6− with H3O+ and [FeCl4]− respectively, we obtained a new molecular ferroelectric [H3O(18‐crown‐6)]+[FeCl4]−, 1. Compound 1 undergoes a para‐ferroelectric phase transition near 350 K with symmetry change from P21/n to the Pmc21 space group. X‐ray single‐crystal diffraction analysis suggests that the phase transition was mainly triggered by the displacement motion of H3O+ and [FeCl4]− 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. The synthesis of compound ([H3O(18‐crown‐6)]+[FeCl4]−) that crystallizes at polar point groups at room temperature by molecular design is reported. It displays high dielectric response and extremely strong second harmonic generation (SHG).