Zeolites embrace metal-organic frameworks: building block approach to the design and synthesis of zeolite-like metal-organic frameworks (ZMOFs)

Our research group has recently developed a novel approach to the design and synthesis of metal-organic assemblies (MOAs), e.g. metal-organic frameworks and metal-organic polyhedra, which has permitted the construction of anionic zeolite-like metal-organic frameworks (ZMOFs), i.e. rho-ZMOF and sod-ZMOF, serving to merge two important classes of porous functional materials, namely zeolites and metal-organic frameworks (MOFs). Though the use of tetrahedral divalent single-metal ions (M²⁺) and simple angular monovalent ligands (L^-) may lead to MOFs with zeolite-like topologies, the resultant frameworks will be neutral and preclude the use of cationic structure-directing agents (SDAs) and limit the diversity of structures constructed from the same metal ion M(II) and ligand (L^-). Our design strategy involves targeting rigid and directional single-metal-ion-based molecular building blocks (MBBs), namely MN_x+y(CO₂)_x+z (containing x N-, O- chelates, y additional N-moieties, and z bridging carboxylates at the remaining open metal sites), where M is a 6- or 8-coordinate metal and the multi-valent, multifunctional ligand is judiciously selected depending on the target structure. The focus of the approach has been to render each hetero-coordinated (N-, O-) single-metal ion, formed in situ, rigid and directional using the N-, O-chelating moieties. For the formation of anionic ZMOFs, an angular ligand (L^2-) is utilized where the M-N bonds direct the topology, while the oxygen atoms complete the coordination sphere of the metal and lock it into its position through the formation of rigid five-membered rings via chelation. Our strategy allows for the use of cationic SDAs and thus offers great potential to access the diverse library of known zeolite topologies, including theoretical ones.