Freude D, Loeser T, Michel D, Pingel U, Prochnow D
Fakultät für Physik und Geowissenschaften, Universität Leipzig, Germany.
Solid State Nucl Magn Reson. 2001 Aug-Sep;20(1-2):46-60. doi: 10.1006/snmr.2001.0029.
Multiple-quantum magic-angle spinning and double-rotation NMR techniques were applied in the high field of 17.6 T to the study of oxygen-17-enriched zeolites A and LSX with the ratio Si/Al = 1. A monotonic correlation between the isotropic value of the chemical shift and the Si-O-Al bond angle alpha (taken from X-ray data) could be found. Hydration of the zeolites causes a downfield 17O NMR chemical shift of about 8 ppm with respect to the dehydrated zeolites. Ion exchange of the hydrated zeolites generates stronger chemical shift effects. The increase of the basicity of the oxygen framework of the zeolite LSX is reflected by a downfield shift of approx. 10 ppm going from the lithium to the cesium form, and the substitution of sodium by thallium in the zeolite A causes a shift of 34 ppm for the O3 signal. 17O DOR NMR spectra are superior to 17O 3QMAS NMR spectra, featuring a resolution increase by a factor of 2 and are about equal with respect to the sensitivity. The residual linewidths of the signals in the 17O DOR and 17O 5QMAS NMR spectra can be explained by a distribution of the Si-O-Al angles in the zeolites.
多量子魔角旋转和双旋转核磁共振技术被应用于17.6 T的高场中，用于研究硅铝比为1的富氧-17的A型和LSX型沸石。可以发现化学位移的各向同性值与Si-O-Al键角α（取自X射线数据）之间存在单调相关性。沸石的水合作用相对于脱水沸石会导致约8 ppm的17O核磁共振化学位移向低场移动。水合沸石的离子交换会产生更强的化学位移效应。沸石LSX的氧骨架碱性增加表现为从锂型到铯型约有10 ppm的低场位移，而沸石A中铊取代钠会使O3信号产生34 ppm的位移。17O双旋转核磁共振谱优于17O多量子魔角旋转核磁共振谱，分辨率提高了2倍，灵敏度大致相当。17O双旋转核磁共振谱和17O五量子魔角旋转核磁共振谱中信号的剩余线宽可以通过沸石中Si-O-Al角的分布来解释。
