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Tuning Nitric Oxide Adsorption in Cobalt–Triazolate Frameworks

preprint
submitted on 08.09.2020 and posted on 09.09.2020 by Julia Oktawiec, Henry Z. H. Jiang, Ari Turkiewicz, Jeffrey R. Long

Nitric oxide (NO) is an important signaling molecule in biological systems, and as such the ability of certain porous materials to reversibly adsorb NO is of interest for medical applications. Metal–organic frameworks have been explored for their ability to reversibly bind NO at coordinatively-unsaturated metal sites, however the influence of metal coordination environment on NO adsorption has yet to be studied in detail. Here, we examine NO adsorption in the frameworks Co2Cl2(bbta) and Co2(OH)2(bbta) (H2bbta = 1H,5H-benzo(1,2-d:4,5-d′)bistriazole) via gas adsorption, infrared spectroscopy, powder X-ray diffaction, and magnetometry measurements. While NO adsorbs reversibly in Co2Cl2(bbta) without electron-transfer, adsorption of low pressures of NO in Co2(OH)2(bbta) is accompanied by charge transfer from the cobalt(II) centers to form a cobalt(III)–NO adduct, as supported by diffraction and infrared spectroscopy data. At higher pressures of NO, characterization data support additional uptake of the gas and disproportionation of the bound NO to form a cobalt(III)–nitro (NO2) species and N2O gas, a transformation that appears to be facilitated in part by stabilizing hydrogen bonding interactions between the bound NO2 and framework hydroxo groups. This reactivity represents a rare example of reductive NO-binding in a metal–organic framework and demonstrates that NO binding can be tuned by changing the coordination environment of the framework metal centers.

Funding

Interrogating Selective Metal-Adsorbate Interactions in Metal-Organic Frameworks

Basic Energy Sciences

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History

Email Address of Submitting Author

jrlong@berkeley.edu

Institution

University of California, Berkeley

Country

United States

ORCID For Submitting Author

0000-0002-2895-3327

Declaration of Conflict of Interest

No conflict of interest.

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