Organization of Lithium Cubane Clusters into Three-Dimensional Porous Frameworks by Self-Penetration and Self-Polymerization

Metal-organic frameworks based on lithium inherit the unique chemical and structural features of the metal ion itself. While the monomeric lithium node, usually 4 connected, is very desirable for designing zeolite-type networks, the resulting lithium MOF usually has limited stability, especially for 3-connected nets due to the solvent termination. The conventional design strategy based on lithium aryloxide clusters makes use of phenol-type ligands for cluster formation and a separate bifunctional ligand for cross-linking, which also leads to 4-connected nets. By integrating the roles of cluster-formation and framework formation into a single ligand, 4-hydroxypyridine was previously shown to give a highly stable 8-connected framework. Still, its shortness and rigidity limit both the porosity and the type of framework topologies. In this work, we demonstrate the new chemical and structural features of lithium cubane clusters with an elongated ligand, which results in two high-connected 3-D framework materials characterized by self-penetration and self-polymerization, respectively, unlike the commonly observed interpenetration. Such a method provides a feasible path to tune both stability and porosity in lithium-based MOFs.