Advances in Symmetry-Based Pulse Sequences in Magic-Angle Spinning Solid-State NMR

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

“…Moreover, solid-state NMR may also unveil information across the "difficult" 0.3-1 nm length-scale, unlike other spectroscopies, such as infrared and Raman. Here the through-space mediated dipolar interaction constitutes the key NMR tool for the structural probing [1][2][3][4][5][6][7]. The dipolar-interaction strength in a pair of homonuclear spins j and k is given by the dipolar coupling constant (b jk ; in Hz), which depends on the inverse cube of the j-k distance (r jk ) according to b jk = −µ 0h γ 2 r −3 jk /(8π 2 ), where γ is the gyromagnetic ratio [3][4][5].…”

“…The dipolar-interaction strength in a pair of homonuclear spins j and k is given by the dipolar coupling constant (b jk ; in Hz), which depends on the inverse cube of the j-k distance (r jk ) according to b jk = −µ 0h γ 2 r −3 jk /(8π 2 ), where γ is the gyromagnetic ratio [3][4][5]. The utilization of dipolar recoupling for retrieving both qualitative information about interatomic proximities and quantitative interatomic distances is nowadays exploited routinely in MAS NMR [1][2][3][4][5][6][7]. Implementations normally require application of dipolar recoupling radio-frequency (rf) pulse sequences to "recouple" (i.e., restore) the dipolar effects (which are otherwise suppressed by MAS) in a controlled fashion [3][4][5][6][7].…”

“…The engineering of rf-pulse sequences to achieve homonuclear dipolar recoupling among spins-1/2 (e.g., 1 H, 13 C, and 31 P) is well-developed [3][4][5][6][7], whereas it is exceedingly difficult to devise efficient and robust dipolar recoupling methods for half-integer spin quadrupolar nuclei [8,9], such as the 11 B (spin S = 3/2) and 27 Al (S = 5/2) nuclides considered herein. Underlying these problems is the necessity to solely observe and control the central transition (CT) of the quadrupolar nucleus [10], thereby requiring the lowest possible rf-field amplitudes ("rf power") to avoid NMR-signal leakages out to the satellite transitions (STs) during the dipolar recoupling, while it must also cope with large second-order broadenings (and chemical-shift dispersion for structurally disordered materials [2,10]).…”

Introduction to average Hamiltonian theory. I. Basics

“…These rf schemes are said to recouple certain spin interactions. An almost countless number of such decoupling and recoupling pulse sequences have been designed during the last 50 years for the application in solution and solid‐state NMR spectroscopy often with the crucial help of average Hamiltonian theory …”

A general theoretical description of the influence of isotropic chemical shift in dipolar recoupling experiments for solid-state NMR

“…An example of quite advanced experiments developed by such means are the symmetry-based pulse sequences [14][15][16][17][18]. Here, symmetry arguments have been used to develop selection rules to construct elegant pulse sequences with robust behaviors with respect to challenges such as rf inhomogeneity and large variations in isotropic chemical shifts while ensuring high polarization-transfer efficiency.…”