Direct X-ray Observation of Trapped CO2 in a Predesigned Porphyrinic Metal-Organic Framework

Metal-organic frameworks (MOFs) are emerging microporous materials that are promising for capture and sequestration of CO2 due to their tailorable binding properties. However, it remains a grand challenge to pre-design a MOF with a precise, multivalent binding environment at the molecular level to enhance CO2 capture. Here, we report the design, synthesis, and direct X-ray crystallographic observation of a porphyrinic MOF, UNLPF-2, that contains CO2-specific single molecular traps. Assembled from an octatopic porphyrin ligand with [Co-2(COO)(4)] paddlewheel clusters, UNLPF-2 provides an appropriate distance between the coordinatively unsaturated metal centers, which serve as the ideal binding sites for in situ generated CO2. The coordination of Co-II in the porphyrin macrocycle is crucial and responsible for the formation of the required topology to trap CO2. By repeatedly releasing and recapturing CO2, UNLPL-2 also exhibits recyclability.