Towards the Accurate Calculation of 183W NMR Chemical Shifts in Polyoxometalates: The Relevance of the Structure |
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Authors: | Laia Vilà‐Nadal José?Pedro Sarasa Dr Antonio Rodríguez‐Fortea Dr Joan Igual Dr Leonid?P Kazansky Dr Josep?M Poblet Prof?Dr |
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Institution: | 1. Departament de Química Física i Inorgànica, Universitat Rovira i Virgili c/Marcel?lí Domingo s/n, 43007 Tarragona (Spain), Fax: (+34)?977‐559‐569;2. Departamento de Química Física y Química Orgánica, Universidad de Zaragoza, C. Universitaria s/n 50009‐Zaragoza (Spain);3. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31, Leninskii pr. Moscow (Russian Federation) |
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Abstract: | DFT calculations were carried out to study 183W NMR chemical shifts in the family of the Keggin anions with formula α‐XW12O40]q? (X=B, Al, Si, P, Ga, Ge, As, Zn), in the β‐ and γ‐SiW12O40]4? geometric isomers, in the derivative Dawson anion P2W18O62]6?, and in the most symmetrical Lindqvist W6O19]2? anion and its derivative W10O32]4?. In this article, we show that the geometry employed in the calculation of NMR chemical shifts in polyoxotungstates is extremely important if we want to be quantitative. Using very large basis sets of QZ4P quality and taking into account the conductor‐like screening model (COSMO) to account for solvent effects (aqueous and organic solutions), good geometries were found for the polyoxoanions. From these optimal geometries the 183W NMR chemical shifts were computed with the more standard basis sets of TZP quality and including spin–orbit corrections inside the zero‐order regular approximation (ZORA) to describe the relativistic effects of the internal electrons. With this strategy the mean absolute error between experimental and theoretical values was found to be less than 10 ppm, which is similar to the experimental error. We also discuss how the geometry of the polyoxoanion influences on the shielding. |
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Keywords: | chemical shifts density functional calculations NMR spectroscopy polyoxometalates tungsten |
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