Tailoring porosity and rotational dynamics in a series of octacarboxylate metal-organic frameworks

Modulation and precise control of porosity of metal-organic frameworks (MOFs) is of critical importance to their materials function. Here we report modulation of porosity for a series of isoreticular octacarboxylate MOFs, denoted MFM-180 to MFM-185, via a strategy of selective elongation of metal-or...

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Published inProceedings of the National Academy of Sciences - PNAS Vol. 114; no. 12; pp. 3056 - 3061
Main Authors Moreau, Florian, Kolokolov, Daniil I., Stepanov, Alexander G., Easun, Timothy L., Dailly, Anne, Lewis, William, Blake, Alexander J., Nowell, Harriott, Lennox, Matthew J., Besley, Elena, Yang, Sihai, Schröder, Martin
Format Journal Article
LanguageEnglish
Published United States National Academy of Sciences 21.03.2017
Subjects
Adsorption
Ligands
Metals
Physical Sciences
Porosity
Spectrum analysis
Temperature
copper
molecular rotors
CH4
CO2
metal-organic framework
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Summary:Modulation and precise control of porosity of metal-organic frameworks (MOFs) is of critical importance to their materials function. Here we report modulation of porosity for a series of isoreticular octacarboxylate MOFs, denoted MFM-180 to MFM-185, via a strategy of selective elongation of metal-organic cages. Owing to the high ligand connectivity, these MOFs do not show interpenetration, and are robust structures that have permanent porosity. Interestingly, activated MFM-185a shows a high Brunauer–Emmett–Teller (BET) surface area of 4,734 m² g−1 for an octacarboxylate MOF. These MOFs show remarkable CH₄ and CO₂ adsorption properties, notably with simultaneously high gravimetric and volumetric deliverable CH₄ capacities of 0.24 g g−1 and 163 vol/vol (298 K, 5–65 bar) recorded for MFM-185a due to selective elongation of tubular cages. The dynamics of molecular rotors in deuterated MFM-180a-d16 and MFM-181a-d16 were investigated by variable-temperature ²H solid-state NMR spectroscopy to reveal the reorientation mechanisms within these materials. Analysis of the flipping modes of the mobile phenyl groups, their rotational rates, and transition temperatures paves the way to controlling and understanding the role of molecular rotors through design of organic linkers within porous MOF materials.
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Author contributions: F.M., S.Y., and M.S. designed research; F.M., D.I.K., A.D., W.L., and A.J.B. performed research; A.G.S., A.D., A.J.B., H.N., M.J.L., and E.B. contributed new reagents/analytic tools; F.M., D.I.K., T.L.E., and S.Y. analyzed data; and F.M., D.I.K., A.G.S., T.L.E., A.D., W.L., A.J.B., H.N., M.J.L., E.B., S.Y., and M.S. wrote the paper.
Edited by Omar M. Yaghi, University of California, Berkeley/Lawrence Berkeley National Laboratory, Berkeley, CA, and accepted by Editorial Board Member Thomas E. Mallouk January 25, 2017 (received for review September 10, 2016)
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1615172114