Improved Magnetization Transfers among Quadrupolar Nuclei in Two-Dimensional Homonuclear Correlation NMR Experiments Applied to Inorganic Network Structures

Abstract

We demonstrate that supercycles of previously introduced two-fold symmetry dipolar recoupling schemes may be utilized successfully in homonuclear correlation nuclear magnetic resonance (NMR) spectroscopy for probing proximities among half-integer spin quadrupolar nuclei in network materials undergoing magic-angle-spinning (MAS). These (SR2 2 1 ) M , (SR2 4 1 ) M , and (SR2 8 1 )M recoupling sequences with M = 3 and M = 4 offer comparably efficient magnetization transfers in single-quantum–single-quantum (1Q–1Q) correlation NMR experiments under moderately fast MAS conditions, as demonstrated at 14.1 T and 24 kHz MAS in the contexts of 11 B NMR on a Na 2 O–CaO–B 2 O 3 –SiO 2 glass and 27 Al NMR on the open framework aluminophosphate AlPO-CJ19 [(NH 4 ) 2 Al 4 (PO 4 ) 4 HPO 4 · H 2 O]. Numerically simulated magnetization transfers in spin–3/2 pairs revealed a progressively enhanced tolerance to resonance offsets and rf-amplitude errors of the recoupling pulses along the series (SR2 2 1 ) M < (SR2 4 1 ) M < (SR2 8 1 )M for increasing differences in chemical shifts between the two nuclei. Nonetheless, for scenarios of a relatively minor chemical-shift dispersions ( ≲ 3 kHz), the (SR2 2 1 )M supercycles perform best both experimentally and in simulations.

On the use of radio‐frequency offsets for improving double‐quantum homonuclear dipolar recoupling of half‐integer‐spin quadrupolar nuclei

“…These oscillations have already been previously explained owing to interference between the first-order quadrupolar interaction and the RF pulses. [41] Simulations (reported in Figure S3) clearly confirm this point but also prove that the dipolar interaction is involved. This is notably illustrated by comparing the oscillatory responses of S 3 and [S 3 ] when changing the relative orientation of the 27 Al EFG tensor to the crystal-fixed frame (see Figure S3a,d) or the 27 Al- 27 Al dipolar vector (see Figure S3b,e) with respect to those in Figure S3c,f, respectively.…”

“…[40] Very recently, these S p sequences have been applied to correlate the CTs of half-integerspin quadrupolar nuclei in the single-quantum-singlequantum (SQ-SQ) manner. [41,42] In this work, we compare the performances of BR2 1 2 and S 3 recoupling sequences for DQ-SQ homonuclear correlation between 27 Al (I = 5/2) nuclei, and also further explore the underlying spin dynamics. Numerical and experimental evaluations are presented, and a comprehensive theoretical description is provided to explain the superiority of BR2 1 2 over other recoupling sequences in terms of DQ transfer efficiency and bandwidth.…”

Advances in the characterization of inorganic solids using NMR correlation experiments

“…In particular, efficient recoupling has been achieved using homonuclear rotary recoupling (HORROR) condition, ν nut CT = (𝐼 + 1/2)𝜈 1 = 𝜈 𝑅 /2, where ν nut CT is the nutation frequency of the CT and ν1 is the rf field strength 149 . The robustness to offset and rf field inhomogeneity has been improved by the use of R𝑁 𝑛 𝜈 symmetry-based recoupling and supercycling [150][151][152][153][154][155] . Zeroquantum (0Q) dipolar recoupling, such as SR2 2 1 , can be employed to acquire 2D 1Q-1Q correlation spectra 150,153,154 , whereas 2Q recoupling, such as BR2 2 1 , can be applied to record 2D 2Q-1Q correlation experiments 151,152,155 .…”

“…The robustness to offset and rf field inhomogeneity has been improved by the use of R𝑁 𝑛 𝜈 symmetry-based recoupling and supercycling [150][151][152][153][154][155] . Zeroquantum (0Q) dipolar recoupling, such as SR2 2 1 , can be employed to acquire 2D 1Q-1Q correlation spectra 150,153,154 , whereas 2Q recoupling, such as BR2 2 1 , can be applied to record 2D 2Q-1Q correlation experiments 151,152,155 . The 1Q-1Q correlation pulse sequence is identical to that shown in Figure 7a, except that the 90° pulse are selective of the CT and 0Q recoupling scheme is applied during the  delay.…”

Editorial for the Special Issue on Solid-State NMR Spectroscopy in Materials Chemistry

“…Moreover, another research avenue of solid-state NMR concerns the development of new rf-pulse sequences for extracting structural information, such as NMR parameters that reflect the local structure, as well as distance/proximity information provided by the dipolar interactions. An article in this Special Issue by Yu et al [7] presents new rf-pulse schemes for probing (for instance) the inter-connectivities of borate groups in B-bearing glasses via 11 B-11 B dipolar interactions. Yu et al demonstrated their technique on a borosilicate glass, but it is equally applicable to the borophosphate counterparts reviewed in reference [4].…”