Introducing dynamic behavior into periodic frameworks has borne fruit in the form of flexible porous crystals. The detailed molecular design of frameworks in order to control their collective dynamics is of particular interest, for example, to achieve stimulus-induced behavior. Herein, by varying the degree of rigidity of ditopic pillar linkers, two isostructural flexible metal–organic frameworks (MOFs) with common rigid supermolecular building bilayers were constructed. The subtle substitution of single (in bibenzyl-4,4′-dicarboxylic acid; H₂BBDC) with double (in 4,4′-stilbenedicarboxylic acid; H₂SDC) C–C bonds in pillared linkers led to markedly different flexible behavior of these two MOFs. Upon the removal of guest molecules, both frameworks clearly show reversible single-crystal-to-single-crystal transformations involving the cis–trans conformation change and a resulting swing of the corresponding pillar linkers, which gives rise to Flex-Cd-MOF-1a and Flex-Cd-MOF-2a, respectively. Strikingly, a more favorable gas-induced dynamic behavior in Flex-Cd-MOF-2a was verified in detail by stepwise C₃H₆/C₃H₈ sorption isotherms and the corresponding in situ powder X-ray diffraction experiments. These insights are strongly supported by molecular modeling studies on the sorption mechanism that explores the sorption landscape. Furthermore, a consistency between the macroscopic elasticity and microscopic flexibility of Flex-Cd-MOF-2 was observed. This work fuels a growing interest in developing MOFs with desired chemomechanical functions and presents detailed insights into the origins of flexible MOFs.

中文翻译：

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通过调节模块刚性来调节柔性晶体的刺激诱导动态行为


将动态行为引入周期性框架已经取得了柔性多孔晶体形式的成果。为了控制其集体动力学而对框架进行详细的分子设计特别令人感兴趣，例如，实现刺激诱导的行为。在此，通过改变双位柱连接体的刚性程度，构建了两种具有常见刚性超分子结构双层的同构柔性金属有机框架（MOF）。单（在联苄基-4,4'-二甲酸中；H ₂ BBDC）与双（在 4,4'-二苯乙烯二甲酸中；H ₂ SDC）C 的微妙取代柱状连接体中的 –C 键导致这两种 MOF 的柔性行为显着不同。去除客体分子后，两个框架都清楚地显示出可逆的单晶到单晶的转变，涉及顺反构象变化以及相应的柱连接体的摆动，从而产生 Flex-Cd-MOF-1a和Flex-Cd-MOF-2a，分别。引人注目的是，通过逐步 C ₃ H ₆ /C ₃ H 详细验证了 Flex-Cd-MOF-2a 中更有利的气体诱导动态行为 ₈ 吸附等温线及相应的原位粉末X射线衍射实验。这些见解得到了探索吸附景观的吸附机制分子模型研究的有力支持。此外，观察到 Flex-Cd-MOF-2 的宏观弹性和微观柔性之间的一致性。这项工作激发了人们对开发具有所需化学机械功能的 MOF 的兴趣，并提出了对柔性 MOF 起源的详细见解。