Grossmann G, Potrzebowski M J, Fleischer U, Krüger K, Malkina O L, Ciesielski W
Institut für Analytische Chemie, Technische Universität Dresden, Germany.
Solid State Nucl Magn Reson. 1998 Nov;13(1-2):71-85. doi: 10.1016/s0926-2040(98)00077-0.
The 31P and 77Se magic angle spinning (MAS) nuclear magnetic resonance (NMR) experiments for selenium-77 enriched (70%) trimethylphosphine selenide 1 and triphenylphosphine selenide 2 were carried out in order to determine the nuclear magnetic shielding tensors of both nuclei and to establish values of the phosphorus-selenium indirect spin-spin coupling anisotropy delta J. The m = +1/2 and m = -1/2 subspectra were analysed by the dipolar-splitting-ratio method of Eichele and Wasylischen. For the C(S) molecule 1, delta J was obtained to be +640 +/- 260 Hz from the 31P spectrum and +550 +/- 140 Hz from the 77Se spectrum. Density functional theory (DFT) calculations give a delta J value of about +705 Hz. The value of delta J could not be determined unambiguously by analysis of the 31P spectra for the C1 molecules 2; nevertheless, an estimation of delta J was possible. The principal axis 3 of the phosphorus shielding tensor was determined to be nearly parallel to the PSe bond in 1 and 2. For the selenium shielding of 1, the same orientation was found, whereas in 2, the principal axis 2 of the selenium shielding was found to be oriented nearly along the PSe bond. The experimentally determined phosphorus nuclear magnetic shielding tensors agree well with those calculated by the IGLO method. For those two principal values of the selenium-shielding tensors corresponding to directions nearly perpendicular to the SeP bond, the agreement between calculated and experimental values is satisfactory. For the third one, corresponding to the principal axis close to the SeP bond, the calculated deshielding contributions are distinctly too small for both compounds investigated. Trends observed for the calculated molecular orbital (MO) contributions to the shielding as well as possible reasons for the underestimation of the deshielding contributions along the SeP bond are discussed.
对富含硒 - 77（70%）的三甲基膦硒化物1和三苯基膦硒化物2进行了31P和77Se魔角旋转（MAS）核磁共振（NMR）实验，目的是确定这两种原子核的核磁屏蔽张量，并确定磷 - 硒间接自旋 - 自旋耦合各向异性δJ的值。采用Eichele和Wasylischen的偶极分裂比方法分析了m = +1/2和m = -1/2子谱。对于C(S)分子1，从31P谱得到δJ为 +640 ± 260 Hz，从77Se谱得到 +550 ± 140 Hz。密度泛函理论（DFT）计算给出的δJ值约为 +705 Hz。通过对C1分子2的31P谱分析无法明确确定δJ的值；不过，对δJ进行估计是可能的。磷屏蔽张量的主轴3在1和2中被确定为几乎与PSe键平行。对于1的硒屏蔽，发现了相同的取向，而在2中，硒屏蔽的主轴2被发现几乎沿着PSe键取向。实验测定的磷核磁屏蔽张量与通过IGLO方法计算的结果吻合良好。对于硒屏蔽张量对应于几乎垂直于SeP键方向的两个主值，计算值与实验值之间的吻合令人满意。对于对应于靠近SeP键主轴的第三个值，对于所研究的两种化合物，计算出的去屏蔽贡献明显过小。讨论了计算得到的分子轨道（MO）对屏蔽的贡献所观察到的趋势以及沿SeP键去屏蔽贡献被低估的可能原因。
