Examples of Hartmann–Hahn Match Conditions for CP/MAS between Two Half-Integer Quadrupolar Nuclei

Synthesis and characterization of aluminum diboride products using 27Al, 11B NMR and ab initio studies

“…Despite its assignment as the resonance for AlB 2 in Ref. [12], the peak around 1680 ppm, showing spinning sidebands, has been identified as the Knight shift for aluminum metal [35,36]. The assignment of this peak as attributed to aluminum metal has been experimentally confirmed by the addition of aluminum powder to the sample [14] and is in agreement with the results found here.…”

“…Figure 3 shows the 27 Al MAS spectrum of the commercial AlB 2 sample from Sigma-Aldrich that contains three resonances. As mentioned in the ''Introduction,'' the literature for AlB 2 reports three different 27 Al shifts at 1640 ppm [12], 880 ppm [13,15,17], and 100 ppm [18]. Despite its assignment as the resonance for AlB 2 in Ref.…”

“…Several NMR investigations of AlB 2 have been previously reported [11][12][13][14][15][16][17][18]. However, while there is but a single aluminum site [10] in AlB 2 , the literature for AlB 2 shows spectra with a single 27 Al NMR resonance, but at three different reported shifts of 1640 ppm [12], 880 ppm [13,15,17], and 100 ppm [18].…”

Fast 29Si magic-angle-spinning NMR acquisitions by RAPT-CP 27Al→29Si polarization transfer

“…However, in our case we could not improve the transfers further using this approach; incidentally, our RAPT enhancement of 2.3 is similar to those obtained for spins-5/2 by employing consecutive RAPT-blocks in [9]. Additionally, by careful optimization over larger ranges of spinning frequencies and RF nutation frequencies, it may be possible to find more beneficial cross-polarization conditions [25][26][27]. Keeping the spinning frequency constant at 7.00 kHz, we employed a rather narrow search of nutation frequencies around the first-order sideband condition x Al nut;CT þ x Si nut ¼ x r [27].…”

Through-space MP-CPMAS experiments between spin-1/2 and half-integer quadrupolar nuclei in solid-state NMR

“…In powdered samples, CP dynamics is strongly anisotropic with respect to crystallite orientation and depends on numerous experimental parameters [11,12]. As a result, in most cases, CW-CPMAS involving quadrupolar nuclei is much less sensitive than the transfer between two spin-1/2 nuclei, especially when two different quadrupolar nuclei are involved [13,14]. To be efficient, the RF-fields must then be very weak, which leads to a large sensitivity to off-resonance irradiation.…”