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 ¹¹B NMR measurements of Lewis acid鈥揵ase adducts of the form R₃AsBR鈥?sub>3 (R = Me, Et, Ph; R鈥?= H, Ph, C₆F₅) were carried out at several magnetic field strengths (e.g., B₀ = 21.14, 11.75, and 7.05 T). The ¹¹B NMR spectra of these adducts exhibit residual dipolar coupling under MAS conditions, allowing for the determination of effective dipolar coupling constants, R_eff(⁷⁵As,¹¹B), as well as the sign of the ⁷⁵As nuclear quadrupolar coupling constants. Values of R_eff(⁷⁵As,¹¹B) range from 500 to 700 Hz. Small isotropic J-couplings are resolved in some cases, and the sign of ¹J(⁷⁵As,¹¹B) is determined. Values of C_Q(⁷⁵As) measured at B₀ = 21.14 T for these triarylborane Lewis acid鈥揵ase adducts range from 鈭?2 卤 2 MHz for Et₃AsB(C₆F₅)₃ to 鈭?46 卤 1 MHz for Ph₃AsBPh₃. For Ph₃AsBH₃, two crystallographically nonequivalent sites are identified with C_Q(⁷⁵As) values of 鈭?53 and 鈭?51 卤 1 MHz. For the uncoordinated Lewis base, Ph₃As, four ⁷⁵As sites with C_Q(⁷⁵As) values ranging from 193.5 to 194.4 卤 2 MHz are identified. At these applied magnetic field strengths, the ⁷⁵As quadrupolar interaction does not satisfy high-field approximation criteria, and thus, an exact treatment was used to describe this interaction in ¹¹B and ⁷⁵As 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 ⁷⁵As NMR spectroscopy and serve as examples of spin鈥搒pin-coupled quadrupolar spin pairs, which are also rarely treated in the literature.