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 MNx+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 heterocoordinated (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 (L2-) 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.
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