Selective Gas Uptake and Rotational Dynamics in a (3,24)-Connected Metal-Organic Framework Material

William J.F. Trenholme, Daniil I. Kolokolov, Michelle Bound, Stephen P. Argent, Jamie A. Gould, Jiangnan Li, Sarah A. Barnett, Alexander J. Blake, Alexander G. Stepanov, Elena Besley, Timothy L. Easun, Sihai Yang, Martin Schröder

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Abstract

The desolvated (3,24)-connected metal-organic framework (MOF) material, MFM-160a, [Cu3(L)(H2O)3] [H6L = 1,3,5-triazine-2,4,6-tris(aminophenyl-4-isophthalic acid)], exhibits excellent high-pressure uptake of CO2 (110 wt% at 20 bar, 298 K) and highly selective separation of C2 hydrocarbons from CH4 at 1 bar pressure. Henry's law selectivities of 79:1 for C2H2:CH4 and 70:1 for C2H4:CH4 at 298 K are observed, consistent with ideal adsorption solution theory (IAST) predictions. Significantly, MFM-160a shows a selectivity of 16:1 for C2H2:CO2. Solid-state 2H NMR spectroscopic studies on partially deuterated MFM-160-d12 confirm an ultra-low barrier (∼2 kJ mol-1) to rotation of the phenyl group in the activated MOF and a rotation rate 5 orders of magnitude slower than usually observed for solid-state materials (1.4 × 106 Hz cf. 1011-1013 Hz). Upon introduction of CO2 or C2H2 into desolvated MFM-160a, this rate of rotation was found to increase with increasing gas pressure, a phenomenon attributed to the weakening of an intramolecular hydrogen bond in the triazine-containing linker upon gas binding. DFT calculations of binding energies and interactions of CO2 and C2H2 around the triazine core are entirely consistent with the 2H NMR spectroscopic observations.

Original languageEnglish
Pages (from-to)3348-3358
Number of pages11
JournalJournal of the American Chemical Society
Volume143
Issue number9
DOIs
Publication statusPublished - 10 Mar 2021

OECD FOS+WOS

  • 2.04 CHEMICAL ENGINEERING
  • 1.06 BIOLOGICAL SCIENCES
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