Isoreticular Three-Dimensional Kagome Metal-Organic Frameworks with Open-Nitrogen-Donor Pillars for Selective Gas Adsorption

Here, we report a double-bent-ligand strategy which addresses a commonly encountered challenge in the construction of pillar-layered structures with corrugated layers which are common for nonlinearly coordinated ligands and low-symmetry chiral ligands. Specifically, we show here that out-of-alignment metal coordination sites between two adjacent and opposing layers caused by in-layer bent-type ligands could be joined by another ligand type with a matching bent angle. Two isoreticular metal-organic frameworks, CPM-63m and CPM-63a, are presented here to illustrate the implementation of this strategy. Specifically, [Zn-2(RCOO)(4)] paddlewheel dimers are bridged by bent FDC2- (H2FDC = 2,5-furandicarboxylic acid) to form neutral kagome layers. The resulting corrugated layers are successfully pillared by bent MTZ(-) (HMTZ = 5-methyltetrazole) or ATZ ligands (HATZ = 5-aminotetrazole). Furthermore, the MTZ(-) and ATZ(-) pillars offer open N-donor sites, and gas sorption studies of N-2, CO2, CH4, C2H2, C2H4, and C2H6 show that these materials are highly porous. In addition, they exhibit interesting inverse ethane/ethylene separation properties and good CO2/CH4 separation.