Formation mechanism of the Ga-13 keggin ion: A combined EXAFS and NMR study

The base hydrolysis of gallium chloride and gallium nitrate was followed by combining Ga-71 NMR and Ga K-edge X-ray absorption spectroscopy measuremen ts. Using such an approach, it can be shown unambiguously that the solution contains various trimeric and tetrameric species in the early hydrolytic s tages before the formation of the Ga-13 polycation. This Keggin-type struct ure would then form by condensation of trimers and tetramers in disagreemen t with all of the previously published models that assume the existence of a monomer either tetrahedral or octahedral. In view of the parallel behavio r of aluminum and gallium, this work can certainly be used to reach a bette r understanding of the hydrolytic chemistry of aluminum. This is of prime i mportance regarding the crucial role of this metal in natural systems and i ts widespread use as a coagulant in water treatment operations.