Adsorptive-dissolution of O2 into the potential nanospace of a densely fluorinated metal-organic framework

Nanoporous solids, including metal-organic frameworks (MOFs), have long been known to capture small molecules by adsorption on their pore surfaces. Liquids are also known to accommodate small molecules by dissolution. These two processes have been recognized as fundamentally distinct phenomena because of the different nature of the medium—solids and liquids. Here, we report a dissolution-like gas accommodation so-called "adsorptive-dissolution" behavior in a MOF (PFAC-2) with pores densely filled with perfluoroalkyl chains. PFAC-2 does not have solvent-accessible voids; nevertheless, it captures oxygen molecules without changing the framework structure, analogous to molecular dissolution into liquids. Moreover, we demonstrate the selective capture of O2 by PFAC-2 in a mixture of O2 and Ar, which are difficult to separate due to their similarities such as boiling point and molecular size. Our results show the integration of molecular adsorption into nanospaces and dissolution into fluorous solvents, which can guide the design of crystalline adsorbents for selective molecular trapping and gas separation. A densely fluorinated nanospace demonstrates the integration of adsorption and dissolution, so-called "adsorptive-dissolution", which enables selective adsorption of O2 over Ar.