Abstract
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.
Highlights
The design of stable adsorbents capable of selectively capturing dioxygen with a high reversible capacity is a crucial goal in functional materials development
In our search for a cooperative, O2-selective metal–organic framework, we initially investigated the known framework Co2Cl2(bbta), which features a high density of coordinatively-unsaturated cobalt(II) ions[31,32], as well as basic nitrogen-donor ligands that should enhance the reducing potential of the metal centers[24]
At 195 K, the O2 adsorption isotherm for Co2(OH)2(bbta) exhibits a sharp rise at low pressures (Fig. 3a), and the material achieves a capacity of ∼3 mmol g−1 (0.47 mmol O2 per mmol Co) at just 25 mbar
Summary
The design of stable adsorbents capable of selectively capturing dioxygen with a high reversible capacity is a crucial goal in functional materials development. In the search for improved, cooperative adsorbents for O2 capture, the active sites of proteins such as hemoglobin, hemerythrin, and hemocyanin can serve as sources of inspiration These sites feature reducing transition metal centers that bind O2 via electron transfer to reversibly generate metal-superoxo or metal-peroxo species[26,27], and crucially these species are often stabilized through directed hydrogen-bonding interactions[28]. Histidine residues in hemoglobin hydrogen bond to the iron-superoxo formed upon O2 uptake[28,29], while in hemerythrin a bridging hydroxo group transfers a proton to iron-bound dioxygen to form a hydroperoxo species (Fig. 2a)[30] These hydrogen bonding interactions are thought to play a key role in reversible O2 binding in these proteins, and may be advantageous for the development of metal–organic frameworks for selective and reversible O2 capture. As a result of the close metal contacts within Co2(OH)2(bbta), O2 interacts more weakly with the cobalt(II) centers upon increased loading, providing the first clear example of an adsorbent material that exhibits negative cooperativity upon gas binding
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
