Phase transitions in three new hybrid crystals: (Me3NR)4[Ni(NCS)6] (R = ethyl, propyl, and butyl)

Understanding the microscopic origin of phase transitions in hybrid crystals is of significant important but challenging for designing novel phase-transition materials. Here, three new hybrid crystals, (Me3NR)4[Ni(NCS)6] (R = ethyl for 1, propyl for 2, and butyl for 3) was synthesized and comprehensively studied on their crystal structures, intermolecular interactions, and phase transitions. They possess a same anti-XeF4 structure mode but exhibit different phase transitions arising from their subtly changed alkyl groups. Specifically, 1 undergoes four-step P21/c–P21/c–P21/c–Pbca–Cmce crystalline transitions at 165, 203, 244, and 280 K, respectively; 2 undergoes three-step P212121–Pbca–P21/n–P1c crystalline transitions at 167, 393, and 410 K, respectively, following by a solid-liquid transition at 453 K; 3 undergoes an iso-space-group P21/n–P21/n crystalline phase transition at 257 K and a solid-liquid transition at 410 K. These instances well demonstrate the key roles of delicate and complicated intermolecular interactions on inducing nontrivial phase transitions in hybrid crystals.