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Issue 3, 2013
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High-resolution solid-state 13C NMR spectroscopy of the paramagnetic metal–organic frameworks, STAM-1 and HKUST-1

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Abstract

Solid-state 13C magic-angle spinning (MAS) NMR spectroscopy is used to investigate the structure of the Cu(II)-based metal–organic frameworks (MOFs), HKUST-1 and STAM-1, and the structural changes occurring within these MOFs upon activation (dehydration). NMR spectroscopy is an attractive technique for the investigation of these materials, owing to its high sensitivity to local structure, without any requirement for longer-range order. However, interactions between nuclei and unpaired electrons in paramagnetic systems (e.g., Cu(II)-based MOFs) pose a considerable challenge, not only for spectral acquisition, but also in the assignment and interpretation of the spectral resonances. Here, we exploit the rapid T1 relaxation of these materials to obtain 13C NMR spectra using a spin-echo pulse sequence at natural abundance levels, and employ frequency-stepped acquisition to ensure uniform excitation of resonances over a wide frequency range. We then utilise selective 13C isotopic labelling of the organic linker molecules to enable an unambiguous assignment of NMR spectra of both MOFs for the first time. We show that the monomethylated linker can be recovered from STAM-1 intact, demonstrating not only the interesting use of this MOF as a protecting group, but also the ability (for both STAM-1 and HKUST-1) to recover isotopically-enriched linkers, thereby reducing significantly the overall cost of the approach.

Graphical abstract: High-resolution solid-state 13C NMR spectroscopy of the paramagnetic metal–organic frameworks, STAM-1 and HKUST-1

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Publication details

The article was received on 29 Sep 2012, accepted on 19 Nov 2012 and first published on 21 Nov 2012


Article type: Paper
DOI: 10.1039/C2CP43445H
Phys. Chem. Chem. Phys., 2013,15, 919-929

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    High-resolution solid-state 13C NMR spectroscopy of the paramagnetic metal–organic frameworks, STAM-1 and HKUST-1

    D. M. Dawson, L. E. Jamieson, M. I. H. Mohideen, A. C. McKinlay, I. A. Smellie, R. Cadou, N. S. Keddie, R. E. Morris and S. E. Ashbrook, Phys. Chem. Chem. Phys., 2013, 15, 919
    DOI: 10.1039/C2CP43445H

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