New Zeolitic Imidazolate Frameworks: From Unprecedented Assembly of Cubic Clusters to Ordered Cooperative Organization of Complementary Ligands

Five 4-connected zeolitic metal imidazolate frameworks have been synthesized by using complementary ligands in combination with fine-tuning of synthetic parameters such as solvent ratio. These materials exhibit four different tetrahedral topologies. In TIF-2 and TIF-3, the cubic double 4-ring units are assembled into two different topologies not previously found in metal imidazolates. TIF-2 possesses one-dimensional 12-ring channels and an unprecedented 4-connected topology. It exhibits permanent microporosity and high thermal stability. TIF-3 is the first known example of metal imidazolates with the zeolitic ACO topology. In TIF-4, TIF-5Zn, and TIF-5Co, two complementary ligands (one small and one large) control the framework topology in a cooperative manner with small ligands favoring small rings (such as 4-rings) and large ligands favoring large rings such as 6- and 8-rings, which highlights the significance of framework building units (i.e., cross-linking ligands) in the control of the framework topology, in distinct contrast with inorganic framework materials (e.g., zeolites) in which the framework topology is primarily controlled by extra-framework structure-directing agents. These new frameworks underline the rich synthetic and structural chemistry of metal-imidazolate-based porous frameworks.