Walder Brennan J, Dey Krishna K, Davis Michael C, Baltisberger Jay H, Grandinetti Philip J
Department of Chemistry, Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, USA.
Department of Physics, Dr. H. S. Gour University, Sagar, Madhya Pradesh 470003, India.
J Chem Phys. 2015 Jan 7;142(1):014201. doi: 10.1063/1.4904548.
A new two-dimensional Nuclear Magnetic Resonance (NMR) experiment to separate and correlate the first-order quadrupolar and chemical/paramagnetic shift interactions is described. This experiment, which we call the shifting-d echo experiment, allows a more precise determination of tensor principal components values and their relative orientation. It is designed using the recently introduced symmetry pathway concept. A comparison of the shifting-d experiment with earlier proposed methods is presented and experimentally illustrated in the case of (2)H (I = 1) paramagnetic shift and quadrupolar tensors of CuCl2⋅2D2O. The benefits of the shifting-d echo experiment over other methods are a factor of two improvement in sensitivity and the suppression of major artifacts. From the 2D lineshape analysis of the shifting-d spectrum, the (2)H quadrupolar coupling parameters are 〈Cq〉 = 118.1 kHz and 〈ηq〉 = 0.88, and the (2)H paramagnetic shift tensor anisotropy parameters are 〈ζP〉 = - 152.5 ppm and 〈ηP〉 = 0.91. The orientation of the quadrupolar coupling principal axis system (PAS) relative to the paramagnetic shift anisotropy principal axis system is given by (α,β,γ)=(π2,π2,0). Using a simple ligand hopping model, the tensor parameters in the absence of exchange are estimated. On the basis of this analysis, the instantaneous principal components and orientation of the quadrupolar coupling are found to be in excellent agreement with previous measurements. A new point dipole model for predicting the paramagnetic shift tensor is proposed yielding significantly better agreement than previously used models. In the new model, the dipoles are displaced from nuclei at positions associated with high electron density in the singly occupied molecular orbital predicted from ligand field theory.
本文描述了一种新的二维核磁共振（NMR）实验，用于分离并关联一阶四极相互作用与化学/顺磁位移相互作用。我们将该实验称为移位d回波实验，它能更精确地确定张量主分量值及其相对取向。该实验是基于最近引入的对称路径概念设计的。文中给出了移位d实验与早期提出的方法的比较，并以CuCl2⋅2D2O的（2）H（I = 1）顺磁位移和四极张量为例进行了实验说明。移位d回波实验相对于其他方法的优势在于灵敏度提高了两倍，并且抑制了主要伪影。通过对移位d谱的二维线形分析，得到（2）H四极耦合参数为〈Cq〉 = 118.1 kHz和〈ηq〉 = 0.88，（2）H顺磁位移张量各向异性参数为〈ζP〉 = - 152.5 ppm和〈ηP〉 = 0.91。四极耦合主轴系（PAS）相对于顺磁位移各向异性主轴系的取向由（α,β,γ）=(π2,π2,0)给出。使用简单的配体跳跃模型，估计了不存在交换时的张量参数。基于此分析，发现四极耦合的瞬时主分量和取向与先前的测量结果非常吻合。提出了一种用于预测顺磁位移张量的新点偶极模型，与先前使用的模型相比，该模型的吻合度显著提高。在新模型中，偶极从原子核位移到配体场理论预测的单占据分子轨道中与高电子密度相关的位置。
