Asymmetric Coordination Designed Heterocrown Ether Host–Guest Ferroelectrics with Ultrahigh Tc

Crown ether compounds have garnered significant research interest for decades due to their unique host–guest supramolecular structure and various properties, such as ferroelectricity. However, although many crown ether derivatives have been developed, only the classical crown ether represented by 18-crown-6 was used as the host for crown ether host–guest-type ferroelectrics, and the heterocrown ether-based ferroelectrics have never been reported. Here, for the first time, we propose the strategy of asymmetric coordination through heterocrown ether as a host molecule to unlock ferroelectricity in metal-crown host–guest assemblies. Compared to the symmetrical coordination of the parent M(NO3)2(18-crown-6) (M = Pb2+ or Cd2+), an asymmetric coordination environment for the M2+ ion was created in M(NO3)2(1-aza-18-crown-6), enabling precise symmetry breaking and inducing ferroelectricity. Remarkably, Pb(NO3)2(1-aza-18-crown-6) exhibits an ultrahigh Tc of 470 K, which represents the maximum value reported to date for crown ether-based ferroelectrics. Such high Tc originates from the synergistic effect of disordered rotation commonly observed in the host–guest compounds and the unique out-of-plane flipping motion of the −NH– group in aza-crown ether. To the best of our knowledge, M(NO3)2(1-aza-18-crown-6) represents the birth of the first heterocrown ether ferroelectric family. Our findings provide a new way to design crown ether host–guest ferroelectrics with high performance and greatly stimulate the further exploration of heterocrown ether ferroelectrics.