Observation of an Intermediate to H2 Binding in a Metal-Organic Framework

Brandon R. Barnett, Hayden A. Evans, Gregory M. Su, Henry Z.H. Jiang, Romit Chakraborty, Didier Banyeretse, Tyler J. Hartman, Madison B. Martinez, Benjamin A. Trump, Jacob D. Tarver, Matthew N. Dods, Lena M. Funke, Jonas Börgel, Jeffrey A. Reimer, Walter S. Drisdell, Katherine E. Hurst, Thomas Gennett, Stephen A. FitzGerald, Craig M. Brown, Martin Head-GordonJeffrey R. Long

Research output: Contribution to journalArticlepeer-review

33 Scopus Citations

Abstract

Coordinatively unsaturated metal sites within certain zeolites and metal-organic frameworks can strongly adsorb a wide array of substrates. While many classical examples involve electron-poor metal cations that interact with adsorbates largely through physical interactions, unsaturated electron-rich metal centers housed within porous frameworks can often chemisorb guests amenable to redox activity or covalent bond formation. Despite the promise that materials bearing such sites hold in addressing myriad challenges in gas separations and storage, very few studies have directly interrogated mechanisms of chemisorption at open metal sites within porous frameworks. Here, we show that nondissociative chemisorption of H2at the trigonal pyramidal Cu+sites in the metal-organic framework CuI-MFU-4loccurs via the intermediacy of a metastable physisorbed precursor species.In situpowder neutron diffraction experiments enable crystallographic characterization of this intermediate, the first time that this has been accomplished for any material. Evidence for a precursor intermediate is also afforded from temperature-programmed desorption and density functional theory calculations. The activation barrier separating the precursor species from the chemisorbed state is shown to correlate with a change in the Cu+coordination environment that enhances π-backbonding with H2. Ultimately, these findings demonstrate that adsorption at framework metal sites does not always follow a concerted pathway and underscore the importance of probing kinetics in the design of next-generation adsorbents.

Original languageAmerican English
Pages (from-to)14884-14894
Number of pages11
JournalJournal of the American Chemical Society
Volume143
Issue number36
DOIs
StatePublished - 15 Sep 2021

Bibliographical note

Publisher Copyright:
© 2021 American Chemical Society

NREL Publication Number

  • NREL/JA-5900-80956

Keywords

  • metal-organic frameworks
  • precursors
  • substrates

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