Moudrakovski Igor L, Ripmeester John A
Steacie Institute for Molecular Sciences, National Research Council, Ottawa, Ontario, Canada K1A 0R6.
J Phys Chem B. 2007 Jan 25;111(3):491-5. doi: 10.1021/jp0667994.
39K Solid State NMR spectra (static and magic angle spinning (MAS)) on a set of potassium salts measured at 21.14 T show that the chemical shift range for K(+) ions in diamagnetic salts is well in excess of 100 ppm contrary to previous assumptions that it was quite small. Inequivalent potassium sites in crystals can be resolved through differences in chemical shifts, with chemically similar sites showing differences of over 10 ppm. The quadrupolar coupling constants obtained from MAS and solid echo experiments on powders cover the range from zero for potassium in cubic environments in halides to over 3 MHz for the highly asymmetric sites in K2CO3. Although the quadrupolar effects generally dominate the 39K spectra, in several instances, we have observed subtle but significant contributions of chemical shift anisotropy with values up to 45 ppm, a first such observation. Careful analysis of static and MAS spectra allows the observation of the various chemical shift and quadrupole coupling tensor components as well as their relative orientations, thereby demonstrating that high-field 39K NMR spectroscopy in the solid state has a substantial sensitivity to the local environment with parameters that will be of considerable value in materials characterization and electronic structure studies.
在21.14 T磁场下对一组钾盐进行的39K固态核磁共振谱（静态和魔角旋转（MAS））测量表明，抗磁性盐中K(+)离子的化学位移范围远超100 ppm，这与之前认为其范围很小的假设相反。晶体中不等价的钾位点可通过化学位移差异分辨出来，化学性质相似的位点化学位移差异超过10 ppm。通过对粉末进行MAS和固体回波实验得到的四极耦合常数范围从卤化物中立方环境下钾的零到K2CO3中高度不对称位点的超过3 MHz。尽管四极效应通常主导39K谱，但在某些情况下，我们观察到化学位移各向异性有微妙但显著的贡献，其值高达45 ppm，这是首次有此类观察。对静态和MAS谱的仔细分析能够观察到各种化学位移和四极耦合张量分量及其相对取向，从而表明固态高场39K核磁共振光谱对局部环境具有显著敏感性，其参数在材料表征和电子结构研究中将具有相当大的价值。
