¹⁷O solid‐state NMR at ultrahigh magnetic field of 35.2 T: Resolution of inequivalent oxygen sites in different phases of MOF MIL‐53(Al)

Abstract

is a member of the most extensively studied metal-organic framework (MOF) families owing to its "flexible" framework and superior stability. 17O solid-state NMR (SSNMR) spectroscopy is an ideal site-specific characterization tool as it probes local oxygen environments. Because oxygen local structure is often altered during phase change, 17 O SSNMR can be used to follow phase transitions. However, 17 O is a challenging nucleus to study via SSNMR due to its low sensitivity and resolution arising from the very low natural abundance of 17 O isotope and its quadrupolar nature. In this work, we describe that by using 17 O isotopic enrichment and performing 17 O SSNMR experiments at an ultrahigh magnetic field of 35.2 T, all chemically and crystallographically inequivalent oxygen sites in two representative MIL-53 (Al) (as-made and water adsorbed) phases can be completely resolved. The number of signals in each phase is consistent with that predicted from the space group refined from powder X-ray diffraction data. The 17 O 1D magicangle spinning (MAS) and 2D triple-quantum MAS (3QMAS) spectra at 35.2 T furnish fine information about the host-guest interactions and the structural changes associated with phase transition. The ability to completely resolve multiple chemically and crystallographically inequivalent oxygen sites in MOFs at very high magnetic field, as illustrated in this work, significantly enhances the potential for using the NMR crystallography approach to determine crystal structures of new MOFs and verify the structures of existing MOFs obtained from refining powder X-ray diffraction data.

From operando Raman mechanochemistry to "NMR crystallography": understanding the structures and interconversion of Zn-terephthalate networks using selective 17O-labelling.

“…isconsistent with what has been recently reported in the17 O NMR literature on MOFs [52],[90]. However,…”

Residue-Specific High-Resolution 17O Solid-State Nuclear Magnetic Resonance of Peptides: Multidimensional Indirect 1H Detection and Magic-Angle Spinning

“…Magnetic fields up to 35.2 T have provided dramatic enhancements in spectral resolution and sensitivity through reduction of the secondorder quadrupolar broadening, as illustrated in spectra of peptides and metal−organic frameworks (MOFs). 2,6,8,13,14 Third, cryogenic magic-angle spinning (MAS) probes and dynamic nuclear polarization have recently been used to yield a multifold increase in much needed spectral sensitivity. 6,15,16 Finally, solid-state NMR methods such as multiple-quantum magic-angle spinning (MQMAS) 17 and satellite-transition magic-angle spinning (STMAS) 18 which provide high-resolution isotropic spectra of half-integer quadrupolar nuclei are becoming increasingly popular for 17 O experiments.…”

“…First, new methods to 17 O label peptides and carbohydrates using synthetic and acid-catalyzed exchange methods have been reported. − Notably, 17 O labeled amino acids have been selectively incorporated into recombinant proteins making 17 O NMR feasible for biomacromolecules. , Recently, mechanochemistry has also been shown to be a robust and economic method for 17 O enrichment of a variety of compounds. − Second, higher field NMR magnets and instrumentation have also contributed greatly to facilitating 17 O NMR spectroscopy. Magnetic fields up to 35.2 T have provided dramatic enhancements in spectral resolution and sensitivity through reduction of the second-order quadrupolar broadening, as illustrated in spectra of peptides and metal–organic frameworks (MOFs). ,,,, Third, cryogenic magic-angle spinning (MAS) probes and dynamic nuclear polarization have recently been used to yield a multifold increase in much needed spectral sensitivity. ,, Finally, solid-state NMR methods such as multiple-quantum magic-angle spinning (MQMAS) and satellite-transition magic-angle spinning (STMAS) which provide high-resolution isotropic spectra of half-integer quadrupolar nuclei are becoming increasingly popular for 17 O experiments.…”

From Operando Raman Mechanochemistry to “NMR Crystallography”: Understanding the Structures and Interconversion of Zn-Terephthalate Networks Using Selective 17O-Labeling

“…The overestimation of C Q , often observed in Table 5, is consistent with what has been recently reported in the 17 O NMR literature on MOFs. 59,100 However, unlike the calculated 13 C NMR parameters, no clear trend between 17 Concerning the phases enriched on the carboxylates, the experimental δ iso ( 17 O) arising from the BDC* ligands of the different structures were found to span between 205.2 and 286.6 ppm (see Figure 4b). ZTA1-*BDC exhibits two clear inequivalent oxygen resonances, as expected from the crystal structure.…”