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

分子骨架材料是一类新兴的材料，它结合了分子丰富的功能和常规固体材料的优点。高比表面积、可调节的孔径和官能团在气体吸附分离、催化和传感等领域具有广泛的应用前景。它们是通过用有机连接物连接金属簇合物(节点)而合成的。有几十个可能的不同形状的节点，几乎任何有机分子都可以用作连接物，从而产生一个巨大的“分子机制”集，用于创建各种各样的多孔MFM。在这些材料中观察到了几个有趣的现象。连接体本身的灵活性及其与每个节点的连接导致材料中的呼吸和门控行为，而不会破坏它们的结晶性。例如，骨架呼吸可以容纳客体分子，否则这些客体分子无法通过孔门。以类似的方式，连接体的小旋转可以创建/破坏用于吸收CO2和H2等气体的理想口袋。虽然这种灵活性是MFM行为的基础，但这种灵活性对这些材料的开发构成了内在的挑战，而且对呼吸现象的基本原子论理解还没有到可以用来设计这些材料的阶段。该项目将为多国机制创建一个所有已知构件的数据库，然后使用该数据库来确定每个构件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个框架结构相关联，并用于为特定应用设计灵活的MFM材料-例如，用于存储能量(氢或甲烷)或分离和提纯气体混合物(如天然气中的氦)。

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).