Effective core potential DFT calculations of nuclear shielding as a tool for the prediction and assignment of the tungsten chemical shift in mono- and polynuclear complexes

The shielding of the W-183 nucleus in mononuclear tungsten complexes and in the Keggin heteropolyoxotungstate PW12O403- has been investigated by a density functional theory (DFT) method with effective core potentials. Calculated [PW12O40]3- shieldings correlate with experimental data, although they are one order of magnitude lower than the experimental values, which is reflected in low slopes (< 0.1) of the correlation lines. The influence of molecular geometry (semi-empirical vs. DFT) on the nuclear shielding is examined. There is a fair correlation between atomic charges at W and nuclear shielding only for species sharing the same formal oxidation state.