Antonio Rodriguez-Fortea^a, Pere Alemany^a, and Tom Ziegler^b .

^aDepartament de Quimica Fisica, Universitat de Barcelona, Barcelona, Catalunya, Spain and ^bDepartment of Chemistry, University of Calgary, Calgary, Alberta, T2N 1N4, Canada

Both Pauli spin-orbit and the zeroth order relativistic approximation (ZORA) have been used in conjunction with the gauge including atomic orbital (GIAO) method based on density functional theory (DFT) to calculate ²⁰⁷Pb and ¹⁸³W NMR chemical shifts. For the tungsten series WO₃S^2-, WO₂S₂^2-, WOS₃^2-, WS₄^2- , WO₄² , W(CO)₆ ,WCl₆ and WF₆, one finds the ¹⁸³W chemical shift to be dominated by paramagnetic contributions, whereas the Fermi-contact contribution induced by spin-orbit coupling is of less importance. On the other hand, in the lead series : Me₃PbCl, Me₃PbBr, Me₃PbI, Me₃PbOMe, Me₃PbSMe, Me₃PbSeMe, Me₃PbNEt₂, Me₂PbCl₂ and PbCl₄ the Fermi-contact term is the trend setting contribution. It is shown that ZORA in general provides chemical shift in better agreement with experiment than the simpler Pauli spin-orbit scheme