Hanna, John V., Pike, Kevin J., Charpentier, Thibault, Kemp, Thomas F., Smith, Mark E., Lucier, Bryan E. G., Schurko, Robert W. and Cahill, Lindsay S. (2010) A Nb-93 solid-state NMR and density functional theory study of four- and six-coordinate niobate systems. Chemistry: A European Journal, Vol.16 (No.10). pp. 3222-3239. doi:10.1002/chem.200901581 ISSN 0947-6539.

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Abstract

A variable B-0 field static (broadline) NMR study of a large suite of niobate materials has enabled the elucidation of high-precision measurement of Nb-93 NMR interaction parameters such as the isotropic chemical shift (delta(iso)), quadrupole coupling constant and asymmetry parameter (C-Q and eta(Q)), chemical shift span/anisotropy and skew/asymmetry (Omega/Delta delta and kappa/eta(delta)) and Euler angles (alpha, beta, gamma) describing the relative orientation of the quadrupolar and chemical shift tensorial frames. These measurements have been augmented with ab initio DFT calculations by using WIEN2k and NMR-CASTEP codes, which corroborate these reported values. Unlike previous assertions made about the inability to detect CSA (chemical shift anisotropy) contributions from Nb-v in most oxo environments, this study emphasises that a thorough variable B-0 approach coupled with the VOCS (variable offset cumulative spectroscopy) technique for the acquisition of undistorted broad (-1/2 <->+1/2) central transition resonances facilitates the unambiguous observation of both quadrupolar and CSA contributions within these Nb-93 broadline data. These measurements reveal that the Nb-93 electric field gradient tensor is a particularly sensitive measure of the immediate and extended environments of the Nb-v positions, with C-Q values in the 0 to > 80 MHz range being measured; similarly, the delta(iso) (covering an approximately 250 ppm range) and Omega values (covering a 0 to approximately 800 ppm range) characteristic of these niobate systems are also sensitive to structural disposition. However, their systematic rationalisation in terms of the Nb-O bond angles and distances defining the immediate Nb-v oxo environment is complicated by longer-range influences that usually involve other heavy elements comprising the structure. It has also been established in this study that the best computational method(s) of analysis for the Nb-93 NMR interaction parameters generated here are the all-electron WIEN2k and the gauge included projector augmented wave (GIPAW) NMR-CASTEP DFT approaches, which account for the short-and long-range symmetries, periodicities and interaction-potential characteristics for all elements (and particularly the heavy elements) in comparison with Gaussian 03 methods, which focus on terminated portions of the total structure.

Item Type:	Journal Article
Subjects:	Q Science > QD Chemistry
Divisions:	Faculty of Science, Engineering and Medicine > Science > Physics
Journal or Publication Title:	Chemistry: A European Journal
Publisher:	Wiley - V C H Verlag GmbH & Co. KGaA
ISSN:	0947-6539
Official Date:	2010
Dates:	Date Event 2010 Published
Volume:	Vol.16
Number:	No.10
Number of Pages:	18
Page Range:	pp. 3222-3239
DOI:	10.1002/chem.200901581
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Funder:	NMR infrastructure at the University of Warwick, Natural Sciences and Engineering Research Council of Canada (NSERC), Canadian Foundation for Innovation (CFI), Ontario Innovation Trust (OIT), University of Windsor, Centre for Catalysis and Materials Research (CCMR), National Sciences and Engineering and Researches Council of Canada (NSERC)

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