High-resolution solid-state 13C NMR spectroscopy of the paramagnetic metal-organic frameworks, STAM-1 and HKUST-1Electronic supplementary information (ESI) available: Synthesis details, analysis of in situ hydration during NMR experiments, information on inversion recovery experiments, solution- and solid-state spectra of diamagnetic model systems, further NMR spectra of CD3-STAM-1, XRD pattern for 13C(1,3,4,5)-STAM-1, details of extraction of 13C-enriched Na2mmbtc from enriched STAM-1, 13C spec

Solid-state 13 C 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 T 1 relaxation of these materials to obtain 13 C 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 13 C 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. Complete 13 C NMR spectra of the paramagnetic MOFs, STAM-1 and HKUST-1 are acquired and assigned conclusively by isotopic labeling.