Spin-orbit effect on the magnetic shielding constant using the ab initio UHF method: tin tetrahalides

The 119Sn NMR chemical shifts of SnX4(X=H, Cl, Br and I) and SnBr4−nIn (n = 1, 2, 3) are calculated by the ab initio UHF method including the spin-orbit (SO) interaction combined with the finite perturbation method. The calculated Sn chemical shifts are in good agreement with experiment when the SO interaction is included. As the halogen ligand becomes heavier, the SO effect increases and the chemical shift moves to a higher field. The normal halogen dependence by the substitution from Cl to I in tin tetrahalides is reproduced only when the SO interaction is included. The origin of the SO effect is ascribed to the Fermi contact term.