Manipulation of Charged Porous Cages as Tunable Platforms for Selective Gas Adsorption

Despite the extensive development of metal-organic framework (MOF) chemistry over the past two decades, systems capable of engag-ing in metal-to-ligand π-backbonding interactions remain limited. Further development of this subset of metal-organic materials is of particular interest for tunable small molecule activation, with potential applications in selective adsorption and catalysis. To complement existing MOFs, our group has focused on expanding the chemistry of porous coordination cages (PCCs) as highly tunable building blocks for porous material design. Porous salts assembled from oppositely charged PCCs are a particularly promising class of materials for accessing highly tunable porous phases. To expand porous salt chemistry, we set out to develop approaches for incorporating coordina-tively unsaturated, π-basic transition metal centers in these materials, as demonstrated, in this case, by their behavior toward carbon mon-oxide chemisorption and activation. In this study, we outline an approach to accessing π-basic ruthenium sites in a charged porous coor-dination cage and explore its incorporation in porous salts. We demonstrate that a non-porous molecular ruthenium complex can simi-larly be incorporated as the charge balancing counterion of a porous cage to access phases that exhibit similar selectivity for carbon mon-oxide chemisorption. We anticipate that the design principles outlined in this study will prove to be of broad utility for tailoring porous salts to diverse applications.