Design and synthesis of highly reticulated organic frameworks

Abstract

Construction of highly complex structures is both a fundamental endeavor in science and an artistic pursuit in topology. In the past decades, highly connected building blocks were heavily relied on unstable metal clusters or metal-organic polyhedrons for which are hard to design and reproduce reliably. Here, we systematically designed and then synthesized a series of organic superstructures extending the connecting sites from 12 to 18 and then 24 by robust covalent bonds. By combining with different metal ions or organic linkages, we obtained a series of metal-organic/covalent-organic frameworks with ultrahigh connectivity. For metal-organic frameworks (MOFs), ultra-high-connectivity organic ligands offer at least three advantages: 1) stable high-connectivity sites for rational design and synthesis of multi-metal nodes to achieve multifunctionalities; 2) the steric hindrance of the highly connected ligand itself is conducive to the formation of unsaturated coordination metal nodes to enhance molecular interactions and the tuning of reaction pathways, and 3) systematically and efficiently build highly connected building blocks in a reliable method. Notably, all metal centers in those MOFs, by using our highly-connected organic ligands (OLs), show a lower coordination number than that in traditional low-connected OLs-based MOFs. When the connectivity of OLs was above 12, multi-metal nodes appeared in all MOFs. For COFs, we designed and synthesized three novel 12-connected frameworks with asc, aea, and shp topologies, respectively. Importantly, gram-scale synthesis of these COFs was also achieved, highlighting the scalability and practical potential of this approach.