SPECTROSCOPIC STUDIES OF GALLIUM COMPLEXES IN SOLUTION

High-field 71Ga NMR spectra at 122.03 MHz of aqueous solutions of Ga3+ in the presence of oxyanions reveal sulphate, phosphate or citrate complexes. In halogen acid solutions the [Ga(H2O)6]3+ signal is accompanied by that of a mixture of [GaXn(H2O)4-n]3-n (X = Cl or Br; n = 1-4) from which a single NMR peak is observed. Aqueous solutions of [GaCl4]- and [GaBr4]- in combination yield one peak due to mixed halides undergoing ligand exchange. The diethyl ether extract of this solution displays the five signals of the complex acids H+(aq)[GaClnBr4-n]- (n = 0-4). The Raman spectrum of this system provides a set of v(GaCl)sym and v(GaBr)sym frequencies. The 17O chemical shift of the [H9O4]+ ion occurs at 15 ppm. Attempts to investigate the halogen exchange process of gallium mixed-halide species by a two-dimensional 71Ga NMR technique are described. 71Ga NMR spectra of mixed-ligand halide/thiocyanate complexes are attributable to species [GaXn(NCS)4-n]- (X = Cl or Br; n = 0-4). Chemical shift trends show the gallium(III) shielding order, Cl < NCS < Br < I. © 1990.