Crystal structures and phase transitions in two new hybrid crystals: (Me3NCH2CH2X)4[Ni(NCS)6] (X = Cl and Br)

Understanding phase transitions in multi-component crystals is of importance for regulating specified functional materials. Herein, we present two new organic-inorganic hybrid crystals, (Me3NCH2CH2X)4[Ni(NCS)6] (X = Cl and Br), revealing distinct phase transitions. Specifically, the Cl-substituted cations weakly interact with discrete inorganic part hence reveal step-wise dynamic changes upon heating, which result in multi-step solid-solid phase transitions (P1¯–P21/n–A2/a–Cmce) including a ferroelastic one with a spontaneous strain of 0.0475. Whereas the Br-substituted cations with larger steric effect prevent the solid-solid phase transition but give a solid-liquid phase transition at above 419 K. The present instances well demonstrate the complicity for multi-component crystals arising from the delicate balance established by abundant weak intermolecular interactions, and inspire the design of novel phase-transition materials by judiciously assembling multi-component crystals.