Field‐stepped ultra‐wideline NMR at up to 36 T: On the inequivalence between field and frequency stepping

Abstract

Field-stepped NMR spectroscopy at up to 36 T using the series-connected hybrid (SCH) magnet at the U.S. National High Magnetic Field Laboratory is demonstrated for acquiring ultra-wideline powder spectra of nuclei with very large quadrupolar interactions. Historically, NMR evolved from the

71Ga NMR Signatures of Lewis and Brønsted Acid Sites in Gallium Silicates Evidenced and Deciphered upon Interaction with Probe Molecules

“…Having identified the presence of two distinct families of Ga surface sites in Ga@SiO 2 using probe molecules, we then turned to 71 Ga NMR, first investigating Ga@SiO 2 at 14.1 and 21.15 T to gain further insights into the structure and distribution of the Ga sites present. Using WURST-QCPMG detection, in combination with a frequency-stepped approach, the NMR spectrum of Ga@SiO 2 was obtained. − ,, The broad and continuous nature of the 71 Ga NMR signal obtained (Figure c) illustrates that there are, most likely, no large domains of Ga oxides, which would result in signals with smaller C Q values and intense maxima, in addition to evidence for [6]-Ga species (δ iso = 0–75 ppm). ,, The shape of the spectrum is consistent with a Czjzek distribution, with an average η of 0.61 …”

“…Using WURST-QCPMG detection, in combination with a frequency-stepped approach, the NMR spectrum of Ga@SiO 2 was obtained. [40][41][42]53,54 The broad and continuous nature of the 71 Ga NMR signal obtained (Figure 2c) illustrates that there are, most likely, no large domains of Ga oxides, which would result in signals with smaller C Q values and intense maxima, in addition to evidence for [6]-Ga species (δ iso = 0−75 ppm). 21,23,43 The shape of the spectrum is consistent with a Czjzek distribution, with an average η of 0.61.…”

Broadband Cross-Polarization to Half-Integer Quadrupolar Nuclei: Wideline Static NMR Spectroscopy

“…Altenhof et al. and Hansen et al previously reported “dips” in the CT patterns of spectra of HIQN with axially symmetric EFG tensors (i.e., distortions away from pattern uniformity in localized frequency regions). − This is attributed to the transfer of polarization between multiple Zeeman states for EFG tensor orientations with β values at or near 54.74°. Isochromats corresponding to these orientations have similar resonance frequencies for the CT and STs (i.e., degenerate or nearly degenerate Zeeman levels in a frame that rotates at ω 0 + ω Q (1) (β) + ω Q (2) (β), herein referred to as the rotating quadrupolar frame (RQF)), making selective manipulation of the CT via RF pulses difficult.…”

NMR Response of the Tetrel Bond Donor

“…The positions of the discontinuities provide sufficient information to determine the NMR parameters with high accuracy and precision. Reasons for intensity differences between experimental and simulated powder patterns may include T 2 anisotropy, preferential crystallite orientation, and interference from satellite transitions . Nonuniform radiofrequency excitation could also contribute; however, care was taken to step the transmitter to acquire uniformly excited subspectra, which were then coadded (see SI).…”