THEORETICAL-STUDY ON METAL NMR CHEMICAL-SHIFTS - GALLIUM COMPOUNDS, GACL4-NBRN-(N=0-4)

Ga NMR chemical shifts of tetrahalogenogallates, GaCl4-nBrn- (n = 0-4), are calculated with the Hartree-Fock/finite perturbation method. For the Ga chemical shift, the diamagnetic contribution sigma(dia) is dominant and the paramagnetic contribution sigma(para) is small. This means that the Ga chemical shifts in the GaCl4-nBrn- series are mainly determined by structural factors such as metal-ligand distance and ligand nuclear charge. This is in sharp contrast to the cases of transition-metal complexes previously reported, in which sigma(para) gives the dominant contribution. The smallness of DELTA(sigma)para in the Ga compounds is attributed to the smallness in the change of the valence electronic structure due to the ligand substitution. On the basis of ab initio results for the GaCl4-nBrn- series, we also analyze the metal chemical shifts for the series of aluminum, gallium, and indium halides, MX4-nYn- (M = Al, Ga, In; X, Y = Cl, Br, I).