H/F Substitution induced switchable coordination bonds in a cyano-bridged hybrid double perovskite ferroelastic

A three-dimensional cyano-bridged double perovskite ferroelastic [(CH3)3NCH2F]2[KFe(CN)6] was constructed by introducing unprecedented switchable C–F–K coordination bonds. H/F substitution not only preserves the basic structure of the parent [(CH3)4N]2[KFe(CN)6] but also affords an m3̄mF2/m-type ferroelastic phase transition.