Homo-Helical Rod Packing as a Path Toward the Highest Density of Guest-Binding Metal Sites in Metal-Organic Frameworks

In porous materials, metal sites with coordinate solvents offer opportunities for many applications, especially those promoted by host-guest chemistry, but such sites are especially hard to create for Li-based materials, because unlike transition metals, lithium does not usually possess a high-enough coordination number for both framework construction and guest binding. This challenge is addressed by mimicking the functional group ratio and metal-to-ligand charge ratio in MOF-74. A family of rod-packing lithium-organic frameworks (CPM-47, CPM-48, and CPM-49) were obtained. These materials exhibit an extremely high density of guest-binding lithium sites. Also unusual is the homo-helical rod-packing in the CPM series, as compared to the hetero-helical rod packing by helices of opposite handedness in MOF-74. This work demonstrates new chemical and structural possibilities in developing a record-setting high density of guest-binding metal sites in inorganic-organic porous materials.