Rationalization of solid-state NMR multi-pulse decoupling strategies: Coupling of spin I = ½ and half-integer quadrupolar nuclei

Abstract

Highlights : Decoupling of heteronuclear scalar interaction between observed ½-spin nucleus and half-integer quadrupolar nuclei  Case of Multi-Pulse (MP) decoupling scheme  Study of the influence of intrinsic material parameters (heteronuclear dipolar and J coupling, quadrupolar interaction, spin nature) and instrumental parameters (MAS rate, pulse field strength) on MP decoupling efficiency and enhancement of spectral resolution  Rationalization of the MP parameterizing and instrumental set up  Combination of numerical approach and experimental data

Application of NMR Crystallography to Highly Disordered Templated Materials: Extensive Local Structural Disorder in the Gallophosphate GaPO-34A

“…In addition, both isotopes of Ga tend to have larger CQ than 27 Al, such that decoupling conditions would likely be more challenging. 55 Such an approach would also be unlikely to yield significant resolution enhancement for a material as disordered as GaPO-34A, in which the linewidths are dominated by a chemical shift distribution. The quadrupolar characteristic of 71 Ga (I = 3/2) means that, despite a shift range here of ~200 ppm, the individual resonances are significantly broadened and overlapped even at an external field strength of 20.0 T (Figure 3e).…”

“…While it has been demonstrated in aluminophosphates that low-power 27 Al decoupling can provide impressive resolution enhancement for 31 P NMR spectra, , such an approach is not as straightforward for GaPOs owing to the two NMR-active isotopes of Ga, 69 Ga ( I = 3/2, 60.1% natural abundance) and 71 Ga ( I = 3/2, 39.9% natural abundance), both of which would need to be decoupled. In addition, both isotopes of Ga tend to have larger C Q than that of 27 Al, such that decoupling conditions would likely be more challenging . Such an approach would also be unlikely to yield significant resolution enhancement for a material as disordered as GaPO-34A, in which the line widths are dominated by a chemical shift distribution.…”

Order–Disorder Diversity of the Solid State by NMR: The Role of Electrical Charges

“…The 29 Si single-pulse (SP) spectrum without 27 Al decoupling of specimen CLBR at 17.6 T shows lower line widths for the six resonances and also slightly lower splittings for each doublet (Figure 24c). However, when a multi-pulse (MP) sequence is applied for decoupling of spin 1/2 and half-integer quadrupolar nuclei [113], in our case between 29 Si and 27 Al nuclei at 17.6 T, to remove the J coupling arising from 2J (Si,Al), the peak splittings disappear and only one single resonance is resolved for each tetrahedral sites, as shown in the 29 Si{ 27 Al} MP 27 Al decoupling MAS NMR spectrum in Figure 24d. Moreover, the 29 Si{ 27 Al} 1D R-INEPT MAS NMR spectrum of this specimen at 17.6 T (Figure 24e) shows even finer resonances and the peak splitting of the T 2 O and T 1 m sites has disappeared, whereas it is still resolved for the T 2 m site.…”