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 den sity functional theory (DFT) method with effective core potentials. Calcula ted PW12O403- shieldings correlate with experimental data, although they ar e one order of magnitude lower than the experimental values, which is refle cted in low slopes (< 0.1) of the correlation lines. The influence of molec ular geometry (semi-empirical vs. DFT) on the nuclear shielding is examined . There is a fair correlation between atomic charges at W and nuclear shiel ding only for species sharing the same formal oxidation state. (C) 2000 Els evier Science B.V. All rights reserved.