MRC up to August 25, 2008

Magnetic Resonance in Chemistry, up to August 25, 2008
and Volume 46 Issue 9 (September 2008)

Heteronuclear dipolar decoupling effects on multiple-quantum and satellite-transition magic-angle spinning NMR spectra
from Magnetic Resonance in Chemistry by S. Ganapathy, L. Delevoye, J. P. Amoureux, P. K. Madhu (Early View)

We here report on the influence of heteronuclear dipolar decoupling on the 27Al 3QMAS, 5QMAS, and the double-quantum filter-satellite-transition magic-angle spinning (DQF-STMAS) spectra of a strongly dipolar-coupled system, gibbsite. The requirements for heteronuclear dipolar decoupling increase with the order of coherence evolving in the indirect dimension of a two-dimensional (2D) experiment. The isotropic line width of the high-resolution 2D spectra, in samples like gibbsite, is composed of four parts: the distribution of isotropic shifts ([delta]ISO, [delta]QIS), the homogeneous broadening related to the proton-proton flip-flop terms, the 27Al[bond]27Al homonulcear dipolar couplings, and the 1H[bond]27Al heteronuclear dipolar couplings. It is shown that, even in the case of gibbsite, where a strong proton-proton bath exists, the main resolution limiting factor in these experiments resides in the 1H[bond]27Al dipolar interaction. Copyright © 2008 John Wiley & Sons, Ltd.
Keywords
solid-state NMR • quadrupolar nuclei • MQMAS • STMAS • homogeneous broadening • heteronuclear broadening • heteronuclear decoupling • TPPM

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Magnetic Resonance in Chemistry
Volume 46 Issue 9, Pages 803 - 810
Multi-nuclear magnetic resonance study of Na3AlF6AlPO4 molten and solidified mixtures
M. Keppert, A. Rakhmatullin, F. Simko, Michael Deschamps, G. M. Haarberg, C. Bessada
Abstract
Phosphorus is one of the predominant impurities in the Hall-Heroult process for industrial aluminium production. The nature of the dissolved phosphorus species in the Na3AlF6AlPO4 system has been investigated by in situ high-temperature (HT) 19F, 23Na, 27Al, 17O, and 31P NMR. The combination of these experiments enables to define the presence of PO43-, AlF52- and (AlF4OPO3)4- anions in the melt, and then the formation of AlOP bonding. Melts solidified at different cooling rates were characterised using various solid-state NMR techniques including multiple quantum magic angle spinning (MQMAS), rotational echo double resonance (REDOR) and heteronuclear single quantum correlation (HSQC). The glass obtained by the rapid quenching of the hypereutectic melt has been carefully described in order to better understand the structure of the melt. Copyright © 2008 John Wiley & Sons, Ltd.
Keywords
high-temperature NMR • solid-state NMR • molten salts • cryolite • aluminium fluoride • phosphate glasses • MQMAS • REDOR • HSQC