(718b) Chiral MOFs: Building Blocks, Features and Design of New Frameworks

Recent advances in the design and synthesis of metal-organic frameworks have demonstrated the potential of this material class. De novo synthesis of new framework types for specific applications requires a sound understanding of not only the synthesis chemistry but also of desirable framework features. In this study, the existing literature on chiral metal-organic frameworks is analyzed by using the CoRE MOF database. This database contains most of the reported MOF structures from the literature [1]. Chiral frameworks are identified either by topology (e.g. srs, unc, lcyâ?¦) or the presence of chiral linkers. Chiral topologies are identified using structural analysis of their 3D nets. Interestingly, only 19 out of the 362 chiral nets in the Reticular Chemistry Structure Resource (RCSR) database are found within reported MOF structures. MOF structures with chiral linkers (or introduced by post synthetic modification) are identified by data mining of article contents.

Analysis of the reported frameworks gives insight into the organic and inorganic building blocks needed to form chiral frameworks. There are 3 main factors mentioned in the literature that contribute to chirality: asymmetric metal nodes, chiral linkers, or helix formation. Interestingly, analysis of the chiral topologies shows that in many cases chirality is the result of symmetry distortion at the metal node by chelation or mixed O- and N-terminated organic linkers. This essentially means that no chiral building blocks are required to create some degree of chirality in the framework. Several asymmetric metal clusters are identified for Zn, Cu, In, Co, Ni, and Cd that are of interest in the design of novel frameworks (no need for chiral linkers). The formation of helixes or warped pore architectures is more likely if a three-connecting organic building block is present rather than 2- or 4-connecting linkers. On the basis of these insights, several new hypothetical structures are proposed and evaluated for chiral separations. The analysis of structural components is complemented with molecular simulations on the adsorption of R- and S-isomers (organic acid, alcohol, amine, amino acids) to establish relationships and compare the impact of key features (linker, node, helix) on the separation potential.

 [1] Chung et al. Chem. Mater., 2014, 26 (21), pp 6185â??6192