Negative cooperativity upon hydrogen bond-stabilized O2 adsorption in a redox-active metal–organic framework

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 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.

Tuning Nitric Oxide Adsorption in Cobalt–Triazolate Frameworks

“…36,37 In the case of O 2 , the strength of adsorption is dramatically enhanced when the framework bridging ligand is changed from chloride to hydroxide. 33,34 This result is consistent with a more electron-rich ligand environment for the cobalt centers in Co2(OH)2(bbta) in comparison to those in Co2Cl2(bbta), which enables them to more readily reduce oxygen. 38 Because NO, like O2, is capable of accepting an electron from transition metals, 7 we sought to investigate how the electronic environment of the two frameworks may also give rise to distinct NO uptake behavior.…”

“…Finally, the oxygen of the NO moiety is resolved at a distance of 3.111(13) Å from the oxygen atom of the nearest bridging hydroxo group, close to that of the combined crystallographic van der Waals radii of two oxygen atoms (3.1 Å). 41 This proximity indicates that hydrogen bonding may contribute to the adsorption of NO at low pressures, 33,34,37 Fig. 2 Structural models determined from analysis of powder X-ray diffraction data for Co2Cl2(bbta) dosed with 2 mbar NO gas (a) and Co2(OH)2(bbta) dosed with 2 mbar (b) and 200 mbar NO gas (c).…”

“…1b) reversibly binds O2 via electron transfer to form a cobalt(III)-superoxo adduct that is stabilized by hydrogen bonding with the bridging hydroxo groups of the framework. 33 In contrast, the related framework Co2Cl2(bbta) ( Fig. 1a) exhibits much weaker uptake of O2 with no associated electron transfer.…”

Influence of the primary and secondary coordination spheres on nitric oxide adsorption and reactivity in cobalt(ii)–triazolate frameworks

“…The frameworks Co2(OH)2(bbta) and Co2Cl2(bbta) have previously been studied as adsorbents for O2 40,41 and CO2, 42 as well as for the electrocatalytic oxidation of water to oxygen and photocatalytic reduction of CO2 to CO. 43,44 These two isostructural frameworks contain hexagonal pores lined with chains of coordinatively unsaturated cobalt centers bridged by triazolate and chloride or hydroxide groups (Fig. 1a).…”

In Situ Tracking of Wetting‐Front Transient Heat Release on a Surface‐Mounted Metal–Organic Framework

“…In principle, the working principle upholds to track the transient heat released by imbibition for ternary, quaternary, and more complex multicomponent liquid mixtures. [41][42][43] However, simplifying current studies of the "prototype," the complexities of multiple host-guest interactions and low camera resolution used here limits the scopes of the current experimental setup to ternary mixtures.…”