Exploitation of flexibility, responsivity and chemical selectivity in switchable pillared layer MOFs for specific gas adsorption and separation – a first-principles approach

可切换柱撑层金属-有机骨架对吸附气体物种具有很高的选择性。如果另外利用DUT-8提供的灵活性，甚至可以提高这种选择性，如Kaskel和Brunner(S2，P1)对CH4和CO2的吸附的例子。在这里，我们将探索如何将灵活性和选择性协同结合起来。定制连接体、柱子和金属中心的潜力提供了丰富多样的材料，这些材料既可以经历重大的结构变化，导致不同的孔体积，也可以经历组成构件的微妙重新排列，这可以使特定的几何图形与目标分子具有特定的相互作用。到目前为止，灵活性和链接器功能之间的相互作用仍然相当未被探索。T1将解决四个关键问题：第一，我们的目标是了解吸附(QP4)和长程有序(QP3)对DUT-8(M)，M=Ni，Cu，Co，Zn的柔韧性的作用。这将与将获得结构数据的S2和T2密切合作进行，T2将通过大型超级单元格的力场计算来支持T1。在这里，我们还将开发一个数值模型，允许估计DUT-8的灵活性取决于热力学条件和吸附气体物种的类型(QP1)。其次，我们将研究DUT-8(M)对二元混合气体(QP4、QF1)的响应性，特别是对造成MOF响应性显著差异的气体。第三，为了指导S2中的合成，我们将调查包括功能化在内的构建块变异是否以及如何影响DUT-8和扩展的DUT-128衍生物(QP1，QF1)的灵活性。最后，我们将阐明具有特定基团的吸附分子的特定结构，并了解它们与骨架(QF2)的相互作用。与P1合作，不同原子核的核磁共振谱将指导我们理解特定的吸附物-MOF相互作用。对于晶格几何结构，我们将支持P2，它使用EPR技术通过在框架的混合金属桨轮中的自旋探针或通过在孔中吸附的自旋携带探针分子(QP2)来跟踪MOF的铰链动力学。

Switchable pillared layer metal-organic frameworks offer high selectivity towards adsorbed gas species. This selectivity can even be enhanced if in addition the flexibility, which is offered by DUT-8, is exploited, as demonstrated for the example of CH4 vs. CO2 adsorption by Kaskel and Brunner (S2, P1). Here, we will explore how flexibility and selectivity can be synergistically combined. The potential to tailor linkers, pillars and metal centers offers a rich diversity of materials that can undergo both significant structural changes, resulting in different pore volumes, and subtle rearrangements of the constituent building blocks, which can enable particular geometries with specific interactions towards target molecules. The interplay between flexibility and linker functionality is still rather unexplored to date. Four key questions will be tackled by T1: First, we aim to understand the role of the adsorbate (QP4) and of the long-range ordering (QP3) on the flexibility of DUT-8(M), M=Ni, Cu, Co, Zn. This will be carried out in close collaboration with S2, where structural data will be obtained, and with T2, supporting T1 with force field calculations of large super cells. Here, we will also develop a numerical model that allows to estimate the flexibility of DUT-8 depending on the thermodynamic conditions and the type of adsorbate gas species (QP1). Second, we will investigate the responsivity of DUT-8(M) towards binary gas mixtures (QP4, QF1), in particular for gases imposing significant differences in responsivity of the MOF. Third, in order to guide synthesis in S2, we will investigate if and how building block variation, including functionalization, will affect the flexibility of DUT-8 and expanded DUT-128 derivatives (QP1, QF1). Finally, we will elucidate the specific structure of adsorbed molecules with specific groups and understand their interaction with the framework (QF2). In collaboration with P1, NMR spectroscopy of various nuclei will guide us to understand the specific adsorbate-MOF interactions. For the lattice geometry, we will support P2, which uses EPR techniques to follow the hinge dynamics of the MOFs either by spin probes in the mixed metal paddle-wheels of the framework or by adsorbed spin-carrying probe molecules in the pore (QP2).