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

A relativistic DFT method (ZORA) is used to calculate the ¹⁸³W and ¹⁷O NMR chemical shifts for the reduced polyoxotungstates W ₅O₁₈W^IINO^3-, γ-SiW ₁₂O₄₀^6-, P₂W₁₈O ₆₂^8-, and W₁₀O₃₂^6- 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 ¹⁷O NMR resonances upon reduction of the polyoxotungstates.