Observation of an Intermediate to H2 Binding in a Metal–organic Framework

Published

November 10, 2020

Author(s)

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

Abstract

Coordinatively-unsaturated metal sites within certain zeolites and metal–organic frameworks can strongly adsorb various molecules. While many classical examples involve electron-poor metal cations that interact with adsorbates largely through electrostatic 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 H₂chemisorption at the trigonal pyramidal Cu⁺sites in the metal–organic framework Cu^I‑MFU-4<i>l </i>occurs via the intermediacy of a metastable physisorbed precursor species. <i>In situ</i>powder neutron diffraction experiments enable crystallographic characterization of this intermediate, the first time that this has been accomplished for any material. Support 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<b>.</b>

Citation

Journal of the American Chemical Society

Volume

143

Issue

36

Pub Type

Journals

Download Paper

https://doi.org/10.1021/jacs.1c07223

Local Download

Keywords

Metal-Organic Framework, Kubas complex, Hydrogen storage

Citation

Barnett, B. , Evans, H. , Su, G. , Jiang, H. , Chakraborty, R. , Banyeretse, D. , Hartman, T. , Martinez, M. , Trump, B. , Tarver, J. , Dods, M. , Drisdell, W. , Hurst, K. , Gennett, T. , FitzGerald, S. , Brown, C. , Head-Gordon, M. and Long, J. (2020), Observation of an Intermediate to H2 Binding in a Metal&#8211;organic Framework, Journal of the American Chemical Society, [online], https://doi.org/10.1021/jacs.1c07223, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=930798 (Accessed October 21, 2025)