Negative cooperativity upon hydrogen bond-stabilized O(2) adsorption in a redox-active metal–organic framework

The design of stable adsorbents capable of selectively capturing dioxygen with a high reversible capacity is a crucial goal in functional materials development. Drawing inspiration from biological O(2) carriers, we demonstrate that coupling metal-based electron transfer with secondary coordination sphere effects in the metal–organic framework Co(2)(OH)(2)(bbta) (H(2)bbta = 1H,5H-benzo(1,2-d:4,5-d′)bistriazole) leads to strong and reversible adsorption of O(2). In particular, moderate-strength hydrogen bonding stabilizes a cobalt(III)-superoxo species formed upon O(2) adsorption. Notably, O(2)-binding in this material weakens as a function of loading, as a result of negative cooperativity arising from electronic effects within the extended framework lattice. This unprecedented behavior extends the tunable properties that can be used to design metal–organic frameworks for adsorption-based applications.