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

The spin-orbit effect on the Ga and In NMR chemical shifts of the gallium and indium tetrahalides compounds, MX4− (M = Ga and In, X = Cl, Br and I), are studied using an ab initio UHF wavefunction and the finite perturbation method as has been proposed previously. The spin-orbit effect of the heavier halogen ligand is large and works to move the chemical shift to higher field, and as a result the calculated shifts show better agreement with experiment. Though the Ga and In chemical shifts are due to the diamagnetic mechanism, the spin-orbit effect appears through the paramagnetic interaction and the dominant term is the metal valence s AO contribution to the Fermi contact term.