Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9594200 | Solid State Nuclear Magnetic Resonance | 2005 | 21 Pages |
Abstract
93Nb solid-state NMR spectra of a series of inorganic niobates with Nb in different oxygen coordination environments were measured. For all studied compounds the chemical shielding and quadrupole tensor parameters were determined using conventional and ultrahigh field NMR facilities, ultrahigh speed MAS, DQ STMAS, solid-echo and computer modeling. It has been demonstrated that the 93Nb isotropic chemical shift is sensitive to the coordination number of Nb sites. For the first time the 93Nb NMR chemical shift scale for NbOx polyhedra in solid materials has been proposed: for four-coordinated Nb sites, the isotropic shifts occur from â650 to â950Â ppm; five-coordinated Nb sites have the isotropic shifts in the range of -900 to -980Â ppm; for six-coordinated Nb sites the isotropic shifts vary from â900 to â1360Â ppm; the shifts from â1200 to â1600Â ppm are typical for seven-coordinated Nb sites; for eight-coordinated Nb sites the shifts are higher than â1400Â ppm. The possible correlation between the value of the isotropic chemical shift and the ionic character of the NbOx-MOy polyhedra association has been suggested. The magnitude of the 93Nb quadrupole coupling constant depends on the local symmetry of Nb sites and may vary from hundreds of kHz to hundreds of MHz.
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Physical Sciences and Engineering
Chemistry
Physical and Theoretical Chemistry
Authors
Olga B. Lapina, Dzhalil F. Khabibulin, Konstantin V. Romanenko, Zhehong Gan, Mikhail G. Zuev, Vladimir N. Krasil'nikov, Vladimir E. Fedorov,