Molecular Probing in a Metal-Organic Framework for Selective Gas Adsorption and Separation.

Metal-organic frameworks (MOFs) hold significant potential for selective gas adsorption and separation. However, it remains challenging to experimentally reveal collective host-guest interactions and cooperative binding sites at the atomic level in nanosized MOFs and thereby rationalize their separation preferences. Here, we report a molecular probing strategy combined with cryo-3D ED for guiding the selective gas adsorption and separation in MOFs. Molecular probes were purposefully selected to map the binding domains of gas adsorbates in the candidate MOF via atomic-level structural analysis by cryo-3D ED, thereby rationalizing which separation scenario the MOF is most likely to favor. As an example, CO2 and Xe probes reveal multiple host-guest interactions in a reported MOF SU-100, including van der Waals force, coordination bonds, and dipole-dipole interactions. Additional adsorption sites based on cooperative dual open metal sites were detected, enabling extra adsorption of gas molecules with a Bδ--Aδ+-Bδ- configuration. Based on above results, the MOF shows remarkable performance for adsorbing SO2, i.e., high uptake, excellent stability, and effective removal of trace SO2 in the presence of CO2 and N2, which is of great importance in the desulfurization of flue gas toward CO2 capture and recycling.