Source abstract
Abstract
A combined experimental and theoretical study of H2 adsorption was carried out in Co-CUK-1 and Mg-CUK-1, two isostructural metal–organic frameworks (MOFs) that consist of M2+ ions (M = Co and Mg) coordinated to pyridine-2,4-dicarboxylate (pdc2–) and OH– ligands. These MOFs possess saturated metal centers in distorted octahedral environments and narrow pore sizes and display high chemical and thermal stability. Previous experimental studies revealed that Co-CUK-1 exhibits a H2 uptake of 183 cm3 g–1 at 77 K/1.0 atm [ Angew. Chem., Int. Ed. 2007, 46, 272−275, DOI: 10.1002/anie.200601627], while that for Mg-CUK-1 under the same conditions is 240 cm3 g–1 on the basis of the experimental measurements carried out herein. The theoretical H2 adsorption isotherms are in close agreement with the corresponding experimental measurements for simulations using electrostatic and polarizable potentials of the adsorbate. Through simulated annealing calculations, it was found that the primary binding site for H2 in both isostructural analogues is localized proximal to the center of the aromatic rings belonging to the pdc2– linkers. Inelastic neutron scattering (INS) spectroscopic studies of H2 adsorbed in both MOFs revealed a rotational tunnelling transition occurring at around 8 meV in the corresponding spectra; this peak represents H2 adsorbed at the primary binding site. Two-dimensional quantum rotation calculations for H2 localized at the primary and secondary binding sites in both MOFs yielded rotational energy levels that are in agreement with the transitions observed in the INS spectra. Even though both M-CUK-1 analogues possess different metal ions, they exhibit similar electrostatic environments, modeled structures at H2 saturation, and rotational potentials for H2 adsorbed at the most favorable adsorption site. Overall, this study demonstrates how important molecular-level details of the H2 adsorption mechanism inside MOF micropores can be derived from a combination of experimental measurements and theoretical calculations using two stable and isostructural MOFs with saturated metal centers and small pore windows as model systems.
Source: openalex_inverted_index · Quality: baseline
Affiliations
Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, CHE205, Tampa, Florida 33620-5250, United States
Department for Solid State Physics and Microelectronics, Faculty of Physics, University of Sofia, 5 James Bourchier Boulevard, Sofia 1164, Bulgaria
Department of Chemistry and Biochemistry, University of Nevada, Las Vegas, Nevada 89154, United States
Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Lichtenbergstraße 1, D-85748 Garching, Germany
Helmholtz-Zentrum Berlin, für Materialien und Energie, Lise-Meitner Campus, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
Department of Chemistry, The University of Texas at Austin, Welch Hall 4.428, 105 East 24th Street, Stop A5300, Austin, Texas 78712-1224, United States
Department of Chemistry and Biochemistry, Texas Tech University, 2500 Broadway, Box 41 061, Lubbock, Texas 79409-1061, United States
Department of Chemistry, North Carolina State University, 2700 Stinson Drive, Cox Hall 506, Raleigh, North Carolina 27607, United States
Funding
Division of Chemistry · Welch Foundation · American Chemical Society Petroleum Research Fund · Division of Materials Research