DFT calculations of the 183W NMR chemical shifts in reduced polyoxotungstates

A relativistic DFT method (ZORA) is used to calculate the W-183 and O-17 NMR chemical shifts for the reduced polyoxotungstates (W5O18WNO3-)-N-II, gamma-SiW12O406-, P2W18O628-, and W10O326- with different degrees of (de) localization of the electrons introduced. Despite some discrepancies in the calculated and experimental data, the calculations adequately describe the changes in the chemical shifts upon reduction. The reduction of a fully oxidized anion is accompanied by an expansion of the geometry. The effect of the charge localization and change in geometry on the chemical shift is evaluated. The shift of the resonance of the tungsten atoms largely depends on the reduced charge acquired upon reduction. On the other hand, those tungsten atoms that do not increase the electron density upon reduction have a negative shift. The calculations also reproduce the negative shifts of all the O-17 NMR resonances upon reduction of the polyoxotung states. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheirn, Germany, 2006)