Hydrogen‐Bonded Engineering Enhancing Phase Transition Temperature in Molecular Perovskite Ferroelastic

Comprehensive Summary The broad operating temperature range is sought for molecular ferroic materials who are expected to be applied to flexible and electronic materials. Hydrogen bonds, an effective force between molecules, are important to regulate the molecule structure and their condition, helping a higher temperature range for ferroic materials. Here, we report a molecular perovskite ferroelastic (Me‐Hdabco)Rb[BF 4 ] 3 (Me‐Hdabco = N ‐methyldabconium) which shows high temperature ( T 1 = 322.5 K and T 2 = 381 K) ferroelastic phase transitions. The ferroelastic phase transition temperature range of (Me‐Hdabco)Rb[BF 4 ] 3 is significantly increased by 71 K compared with [Meda‐bco‐F]Rb[BF 4 ] 3 (Medabco‐F = 1‐fluoro‐4‐methyl‐1,4‐diazoniabicyclo[2.2.2]octane). Structural analysis and thermal analysis demonstrate the ferroelastic phase transition is mainly attributed to dynamic cations order and disorder transformation. Therefore, new hydrogen bonds generated between cations and the Rb 8 [BF 4 ] 12 frame increase their intermolecular force, which is beneficial to improving the phase transition temperature. This finding has an important impact on the utilization of weak interaction forces to design and optimize functional materials.