NMR Chemical Shifts of Metal Centres in Polyoxometalates: Relativistic DFT Predictions

A DFT approach incorporating relativistic corrections and solvent effects was tested for NMR calculations on transition‐metal centres in polyoxometalates. For a monoplatinum decavanadate derivative and a set of dilacunary polyoxotungstates 51V and 183W chemical shifts were calculated at several levels of theoretical treatment regarding solvent, counterion and exchange‐correlation functional. Calculations were performed first in the gas phase to model isolated ions and next in a continuum model for water to evaluate the importance of solvation for the quality of the computed chemical shifts. We show that the use of the orbital‐dependent Kohn–Sham exchange‐correlation functional SAOP in ZORA spin‐orbit calculations with solvent effects included via COSMO substantially improves the agreement between computed results and experimental benchmarks for 51V chemical shifts (atleast, in the case of [H2PtIVV9O28]5–). In the case of dilacunary polyoxotungstates our calculations confirm the necessity of modelling an ion pair in which a counterion is specifically included in the POM lacuna to attain accurate predictions of the corresponding 183W NMR spectra. We show that if the counterion is relatively small (like Li+ and Na+), the explicit location of a water molecule in its vicinity (in addition to the overall COSMO treatment) improves further the accuracy of the correlation between computed and experimental shifts (to less than 5 ppm of the encompassed δ range).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)