Negative Cooperativity upon Hydrogen Bond-Stabilized O2 Adsorption in a Redox-Active Metal-Organic Framework
Julia Oktawiec, Henry Z. H. Jiang, Jenny G. Vitillo, Douglas A. Reed, Lucy E. Darago, Benjamin A Trump, Varinia Bernales, Harriet Li, Kristen A. Colwell, Hiroyasu Furukawa, Craig Brown, Laura Gagliardi, Jeffrey R. Long
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 O2 carriers, we demonstrate that coupling metal-based electron transfer with secondary coordination sphere effects in the metal–organic framework Co2(OH)2(bbta) (H2bbta = 1H,5H-benzo(1,2-d:4,5-d′)bistriazole) leads to strong and reversible adsorption of O2. In particular, moderate-strength hydrogen bonding stabilizes a cobalt(III)-superoxo species formed upon O2 adsorption. Notably, O2-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.