Metal-Organic Framework Goes Perovskite: A Self-Healing Neutral X-Site Perovskite Ferroelastic Crystal

ABX₃-type perovskites and metal-organic frameworks (MOFs) have attracted sustained scientific interest due to their rich functionalities. However, the convergence of these two families, where MOFs adopt the perovskite architecture incorporating neutral X-sites, remains largely unexplored. Moreover, self-healing is notable for its ability to recover from damage, while achieving self-healing in molecular crystals remains a significant challenge. Herein, for the first time, we report a self-healing neutral X-site perovskite ferroelastic crystal (SbF₆)Ag(pyrazine)₃, in which the neutral pyrazine acts as the X-site, in contrast to the anion X-site in conventional perovskites. It undergoes reconstructive mm2Fm-type ferroelastic phase transition at 163 K and order-disorder 4̅3mFmm2-type ferroelastic phase transition at 322 K. Intriguingly, the reconstructive transition involves reversible breaking of Ag⁺-N coordination bonds and the formation of weak Ag⁺···π interactions, which unlocks the self-healing property, distinct from previous reported self-healing mechanisms in molecular crystals. The low-temperature reconstructive transition generates a spontaneous strain nearly ten times larger than that of the high-temperature transition, leading to crystal microcracks that are subsequently healed upon reversible phase recovery. Our discovery opens up a novel strategy to realize self-healing in molecular crystals and demonstrates the neutral X-site ABX₃-type perovskites as a fertile ground for multifunctional materials.