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 transitionmetal 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 (at least, in the case of [H₂Pt^IVV₉O ₂₈]^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).