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Errors in the Calculation of 27Al Nuclear Magnetic Resonance Chemical Shifts
Center of Bioinformatics, University of Electronic Science and Technology of China, No. 4, 2nd Section, Jianshe Road, Chengdu 610054, China
Department of Chemistry, Bryn Mawr College, 101 North Merion Avenue, Bryn Mawr, PA 19010, USA
* Author to whom correspondence should be addressed.
Received: 10 October 2012; in revised form: 2 November 2012 / Accepted: 6 November 2012 / Published: 21 November 2012
Abstract: Computational chemistry is an important tool for signal assignment of 27Al nuclear magnetic resonance spectra in order to elucidate the species of aluminum(III) in aqueous solutions. The accuracy of the popular theoretical models for computing the 27Al chemical shifts was evaluated by comparing the calculated and experimental chemical shifts in more than one hundred aluminum(III) complexes. In order to differentiate the error due to the chemical shielding tensor calculation from that due to the inadequacy of the molecular geometry prediction, single-crystal X-ray diffraction determined structures were used to build the isolated molecule models for calculating the chemical shifts. The results were compared with those obtained using the calculated geometries at the B3LYP/6-31G(d) level. The isotropic chemical shielding constants computed at different levels have strong linear correlations even though the absolute values differ in tens of ppm. The root-mean-square difference between the experimental chemical shifts and the calculated values is approximately 5 ppm for the calculations based on the X-ray structures, but more than 10 ppm for the calculations based on the computed geometries. The result indicates that the popular theoretical models are adequate in calculating the chemical shifts while an accurate molecular geometry is more critical.
Keywords: aluminum-27 NMR; aluminum(III) complexes; computational chemistry; density functional theory
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MDPI and ACS Style
Wang, X.; Wang, C.; Zhao, H. Errors in the Calculation of 27Al Nuclear Magnetic Resonance Chemical Shifts. Int. J. Mol. Sci. 2012, 13, 15420-15446.
Wang X, Wang C, Zhao H. Errors in the Calculation of 27Al Nuclear Magnetic Resonance Chemical Shifts. International Journal of Molecular Sciences. 2012; 13(11):15420-15446.
Wang, Xianlong; Wang, Chengfei; Zhao, Hui. 2012. "Errors in the Calculation of 27Al Nuclear Magnetic Resonance Chemical Shifts." Int. J. Mol. Sci. 13, no. 11: 15420-15446.