Crystalline Supramolecular Gyroscope with a Water Molecule as an Ultrasmall Polar Rotator Modulated by Charge-Assisted Hydrogen Bonds.

A new strategy for the construction of crystalline molecular rotors is presented. The combination of a conformation-modifiable macrocyclic host and two cooperative guests affords one supramolecular gyroscope-like compound, (t-BuNH)(18-crown-6)[ZnCl(HO)], in which the coordinated water molecule functions as an ultrasmall polar rotator, revealed by its significant dielectric relaxation and the molecular dynamics simulations. In addition, such a compound can reversibly undergo a polar-to-polar phase transition triggered by the changed conformation of the 18-crown-6 host, leading to a switchable on/off rotation of water molecule, well controlled by strength and direction of charge-assisted hydrogen bonds.

A near-room-temperature organic-inorganic hybrid ferroelectric: [CHCHCHNH][CdI].

An organic-inorganic hybrid compound, [CHCHCHNH][CdI], exhibits a reversible ferroelectric phase transition at 301/297 K. Switchable dielectric constant, second harmonic generation, and pyroelectricity were synchronously observed accompanied by the order-disorder phase transition. This finding promotes research on molecular ferroelectrics to search for promising multifunctional switching materials at near room temperature.