Regensburg 2010 – wissenschaftliches Programm

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ST: Fachverband Strahlen- und Medizinphysik

ST 7: Nuclear Magnetic Resonance: Frontiers and Applications (CPP and ST)

ST 7.8: Vortrag

Dienstag, 23. März 2010, 15:30–15:45, H48

Complete NMR spectral assignment in gibbsite by first-principle calculations — •Anastasia Vyalikh and Ulrich Scheler — IPF Dresden, Hohe Str. 6, D-01069 Dresden, Germany

The structure of the mineral gibbsite is often considered as a representative of many alumino-silicate clay minerals, and therefore we use it in the present study as a model compound to establish the suitability of the computational method. Here we apply a gradient-corrected DFT method with a plane-wave basis set to assign the crystallographically distinct Al sites in gibbsite and to relate them to the hydroxide network. The experimental observation is based on high-resolution solid-state 27Al NMR and 1H CRAMPS (combined rotation and multipulse spectroscopy) data. On the basis of DFT calculations, the 1H CRAMPS signals have been attributed to six symmetry independent hydrogen atoms and ascribed to two distinct types associated with intralayer and interlayer hydrogen bonds. The 27Al NMR spectrum shows signals for octahedral aluminium only, however with two distinguished signals. The correlation between experimental and theoretical NMR parameters demonstrates that the character of the hydrogen bonds formed by the hydroxide ions is responsible for the structural differentiation of Al sites. That is, the Al-I site (CQ=4.2 MHz) is surrounded by the OH-groups particiating in 4 intralayer and 2 interlayer hydrogen bonds, while the Al-II site (CQ=2.4 MHz) is coordinated by the hydroxides, 2 of which point towards the intralayer cavities and 4 OH-bonds are aligned towards the interlayer gallery.