Origin and Mechanisms of Flexibility in Molecular Framework Materials: A Data-driven, Graph Theoretical Approach

分子骨架材料（Molecular framework materials，MFM）是一种新兴的材料，它结合了分子的功能和常规固体材料的优点。高比表面积、可调孔径和官能团在气体吸附和分离、催化和传感等领域提供了应用。它们是通过将金属簇（节点）与有机连接体连接而合成的。有几十种不同形状的可能节点，几乎任何有机分子都可以用作连接器，从而产生巨大的“分子Meccano”集，用于创建各种各样的多孔MFM。在这些材料中观察到了一些有趣的现象。连接体本身的柔性及其与每个节点的连接导致材料中的呼吸和门控行为，而不破坏其结晶度。例如，骨架呼吸可以接纳客体分子，否则这些分子将无法通过孔门。以类似的方式，小旋转的链接器可以创建/破坏理想的口袋，用于吸收气体，如CO2和H2。虽然基本的MFM的行为，这种灵活性提出了一个固有的挑战，这些材料的发展，到目前为止，基本的原子理解的呼吸现象是不是在它可以用来设计这些材料的阶段。该项目将创建一个包含所有已知的MFM构建块的数据库，然后使用该数据库来确定每个构建块固有的灵活性程度和类型。然后，每个构建块中的灵活性可以与整体框架结构相关联，并用于设计针对特定应用定制的灵活MFM材料-例如存储能量（氢气或甲烷）或分离和纯化气体混合物（例如天然气中的氦气）。

Molecular framework materials (MFMs) are an emerging materials class that combines the immense richness of functionalities of molecules with the advantages of regular solid materials. High surface area, tuneable pore size and functional groups offer applications in fields such as gas adsorption and separation, catalysis and sensing. They are synthesised by joining metal clusters (nodes) with organic linkers. There are several dozen possible nodes of different shapes, and almost any organic molecule can be used as a linker resulting in a huge "Molecular Meccano" set for the creation of a vast variety of porous MFMs. Several interesting phenomena have been observed in these materials. Flexibility in the linkers themselves and their attachment to each node leads to breathing and gating behaviour in the materials, without destroying their crystallinity. Framework breathing, for example, can admit guest molecules that would not otherwise fit through pore gates. In a similar manner, small rotations of linkers can create / destroy ideal pockets for absorption of gases such as CO2 and H2.While fundamental to the behaviour of MFMs, this flexibility poses an inherent challenge to the development of these materials and as yet the fundamental atomistic understanding of the breathing phenomena is not at the stage where it can be employed to design these materials. This project will create a database of all known building blocks for MFMs and then use that database to determine degree and type of flexibility inherent in each building block. The flexibility in each building block can then be related back to the overall framework structures and used to design flexible MFM materials tailored for specific applications - e.g. to store energy (hydrogen or methane) or to separate and purify gas mixtures (such as helium in natural gas).