Bryce David L, Eichele Klaus, Wasylishen Roderick E
Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2.
Inorg Chem. 2003 Aug 25;42(17):5085-96. doi: 10.1021/ic020706p.
Solid-state (17)O NMR spectroscopy is employed to characterize powdered samples of known monoclinic and orthorhombic modifications of (17)O-enriched triphenylphosphine oxide, Ph(3)PO. Precise data on the orientation-dependent (17)O electric field gradient (EFG) and chemical shift (CS) tensors are obtained for both polymorphs. While the (17)O nuclear quadrupolar coupling constants (C(Q)) are essentially identical for the two polymorphs (C(Q) = -4.59 +/- 0.01 MHz (orthorhombic); C(Q) = -4.57 +/- 0.01 MHz (monoclinic)), the spans (Omega) of the CS tensors are distinctly different (Omega = 135 +/- 3 ppm (orthorhombic); Omega = 155 +/- 5 ppm (monoclinic)). The oxygen CS tensor is discussed in terms of Ramsey's theory and the electronic structure of the phosphorus-oxygen bond. The NMR results favor the hemipolar sigma-bonded R(3)P(+)-O(-) end of the resonance structure continuum over the multiple bond representation. Indirect nuclear spin-spin (J) coupling between (31)P and (17)O is observed directly in (17)O magic-angle-spinning (MAS) NMR spectra as well as in (31)P MAS NMR spectra. Ab initio and density-functional theory calculations of the (17)O EFG, CS, and (1)J((31)P,(17)O) tensors have been performed with a variety of basis sets to complement the experimental data. This work describes an interesting spin system for which the CS, quadrupolar, J, and direct dipolar interactions all contribute significantly to the observed (17)O NMR spectra and demonstrates the wealth of information which is available from NMR studies of solid materials.
采用固态(17)O核磁共振光谱对富含(17)O的三苯基氧化膦(Ph(3)PO)已知单斜晶和正交晶变体的粉末样品进行表征。获得了两种多晶型物取向依赖的(17)O电场梯度(EFG)和化学位移(CS)张量的精确数据。虽然两种多晶型物的(17)O核四极耦合常数(C(Q))基本相同(C(Q)= -4.59±0.01 MHz(正交晶);C(Q)= -4.57±0.01 MHz(单斜晶))，但CS张量的跨度(Ω)明显不同(Ω = 135±3 ppm(正交晶);Ω = 155±5 ppm(单斜晶))。根据拉姆齐理论和磷氧键的电子结构对氧CS张量进行了讨论。核磁共振结果表明，共振结构连续体的半极性σ键合R(3)P(+)-O(-)端比多重键表示更有利。在(17)O魔角旋转(MAS)核磁共振谱以及(31)P MAS核磁共振谱中直接观察到(31)P和(17)O之间的间接核自旋-自旋(J)耦合。使用各种基组对(17)O EFG、CS和(1)J((31)P,(17)O)张量进行了从头算和密度泛函理论计算，以补充实验数据。这项工作描述了一个有趣的自旋系统，其中CS、四极、J和直接偶极相互作用都对观察到的(17)O核磁共振谱有显著贡献，并证明了从固体材料的核磁共振研究中可获得丰富的信息。
