Molecular Sieving and Direct Visualization of CO₂ in Binding Pockets of an Ultramicroporous Lanthanide Metal–Organic Framework Platform

Inspired by the structure of carbonic anhydrase, we developed a robust ultramicroporous lanthanide metal–organic framework (MOF) platform (NKMOF-3-Ln), which possesses a porous pocket to selectively bind with CO2 at ambient conditions. Notably, CO2 molecules can be precisely observed in the single-crystal structure of NKMOF-3-Ln. Highly ordered CO2 molecules can strongly interact with the framework via electrostatic interaction of nitrates. We found that the CO2 adsorption capacity and binding energy were gradually enhanced as lanthanide contraction. The strong CO2 binding affinity endows NKMOF-3-Ln with excellent CO2 separation performance, which is verified by experimental breakthrough results. Moreover, because of the specific binding affinity of CO2, NKMOF-3-Eu showed a fluorescence response to CO2.