Spin鈥揝pin Coupling between Quadrupolar Nuclei in Solids: 11B鈥?sup>75As Spin Pairs in Lewis Acid鈥揃ase Adducts

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• 作者：Alexandra Faucher ; Victor V. Terskikh ; Roderick E. Wasylishen
• 刊名：Journal of Physical Chemistry A
• 出版年：2015
• 出版时间：July 9, 2015
• 年：2015
• 卷：119
• 期：27
• 页码：6949-6960
• 全文大小：424K
• ISSN：1520-5215

文摘

Solid-state <sup>11sup>B NMR measurements of Lewis acid鈥揵ase adducts of the form R<sub>3sub>AsBR鈥?sub>3sub> (R = Me, Et, Ph; R鈥?= H, Ph, C<sub>6sub>F<sub>5sub>) were carried out at several magnetic field strengths (e.g., B<sub>0sub> = 21.14, 11.75, and 7.05 T). The <sup>11sup>B NMR spectra of these adducts exhibit residual dipolar coupling under MAS conditions, allowing for the determination of effective dipolar coupling constants, R<sub>effsub>(<sup>75sup>As,<sup>11sup>B), as well as the sign of the <sup>75sup>As nuclear quadrupolar coupling constants. Values of R<sub>effsub>(<sup>75sup>As,<sup>11sup>B) range from 500 to 700 Hz. Small isotropic J-couplings are resolved in some cases, and the sign of <sup>1sup>J(<sup>75sup>As,<sup>11sup>B) is determined. Values of C<sub>Qsub>(<sup>75sup>As) measured at B<sub>0sub> = 21.14 T for these triarylborane Lewis acid鈥揵ase adducts range from 鈭?2 卤 2 MHz for Et<sub>3sub>AsB(C<sub>6sub>F<sub>5sub>)<sub>3sub> to 鈭?46 卤 1 MHz for Ph<sub>3sub>AsBPh<sub>3sub>. For Ph<sub>3sub>AsBH<sub>3sub>, two crystallographically nonequivalent sites are identified with C<sub>Qsub>(<sup>75sup>As) values of 鈭?53 and 鈭?51 卤 1 MHz. For the uncoordinated Lewis base, Ph<sub>3sub>As, four <sup>75sup>As sites with C<sub>Qsub>(<sup>75sup>As) values ranging from 193.5 to 194.4 卤 2 MHz are identified. At these applied magnetic field strengths, the <sup>75sup>As quadrupolar interaction does not satisfy high-field approximation criteria, and thus, an exact treatment was used to describe this interaction in <sup>11sup>B and <sup>75sup>As NMR spectral simulations. NMR parameters calculated using the ADF and CASTEP program packages support the experimentally derived parameters in both magnitude and sign. These experiments add to the limited body of literature on solid-state <sup>75sup>As NMR spectroscopy and serve as examples of spin鈥搒pin-coupled quadrupolar spin pairs, which are also rarely treated in the literature.