Relativistic study of nuclear magnetic shielding constants: tungsten hexahalides and tetraoxide

Relativistic ab initio calculations of the 183W magnetic shielding constant and the chemical shift of WX6(X = F and Cl) and WO42− are presented. The computational method is a combination of the relativistic spin-free no-pair theory and the spin-orbit unrestricted Hartree-Fock method, which has been applied previously to 199Hg magnetic shielding constants. The spin-tree relativistic (SFR) terms, involving the mass velocity and Darwin terms, are shown to be important for 183W shielding constants. The spin-orbit interaction, which is smaller than the SFR term, works differently on WCl6 and WO42−. The effects of relaxing the inner s and p orbitals of W are investigated.