Shape-memory effects and stimuli-induced phase transformations are observed across many types of materials but remain understudied in molecular materials. In this contribution, we revisit the Werner complex, [Ni(4-MePy)₄(NCS)₂] (4-MePy = 4-methylpyridine), a molecular material that has long been known to form Werner clathrates and possess a porous polymorph. Whereas earlier work implied that [Ni(4-MePy)₄(NCS)₂] could be a shape-memory material, we confirmed this to be the case through p-xylene (PX) vapor sorption studies. Specifically, [Ni(4-MePy)₄(NCS)₂] transformed from its reported nonporous α phase to the PX-loaded β phase induced by PX vapour. β reversibly transformed to its porous β′ phase upon PX removal over at least three PX sorption cycles. β′ reverted to α upon heating at 80 °C in a closed vessel. The porosity of β′ was explored by examining its C₃H_x (x = 4, 6, and 8) gas sorption properties, which revealed guest size/shape-dependent sorption behaviour with uptakes of 0.6, 0.9 and 1.6 mol mol⁻¹ for C₃H₈, C₃H₆ and C₃H₄, respectively. Insight into the structural transformations of the α, β, and β′ phases is provided by analysis of their previously reported crystal structures and new density functional theory calculations.

中文翻译：

---

分子材料中的相变和形状记忆效应：重新审视维尔纳配合物 [Ni(4-MePy)4(NCS)2]

在许多类型的材料中都观察到了形状记忆效应和刺激诱导的相变，但在分子材料中仍然没有得到充分研究。在这篇文章中，我们重新审视了维尔纳配合物，[Ni(4-MePy) ₄ (NCS) ₂ ] (4-MePy = 4-甲基吡啶)，这是一种长期以来已知能形成维尔纳包合物并具有多孔多晶型物的分子材料。 。虽然早期的工作表明 [Ni(4-MePy) ₄ (NCS) ₂ ] 可能是一种形状记忆材料，但我们通过对二甲苯(PX) 蒸气吸附研究证实了这一点。具体来说，[Ni(4-MePy) ₄ (NCS) ₂ ]从其报道的无孔α相转变为由PX蒸气诱导的负载PX的β相。在至少三个 PX 吸附循环中去除 PX 后，β可逆地转化为其多孔β ' 相。在密闭容器中加热至 80 °C 时，β'恢复为α 。通过检查其 C ₃ H _x ( x = 4、6 和 8) 气体吸附特性来探索β'的孔隙率，这揭示了客体尺寸/形状依赖性吸附行为，吸收量为 0.6、0.9 和 1.6 mol mol ^-1分别为C ₃ H ₈、C ₃ H ₆和C ₃ H ₄。通过分析先前报道的晶体结构和新的密度泛函理论计算，可以深入了解α、β和β'相的结构转变。