Detection of a new polymeric species formed through the hydrolysis of gallium(III) salt solutions

Abstract

A previously unreported gallium species has been detected which is formed by the hydrolysis of aqueous gallium(III) solutions. N.m.r. studies have shown that this species has a tetrahedrally co-ordinated gallium nucleus whose chemical shift suggests that it is structurally analogous to the central tetrahedral aluminium occurring in the [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ cation. The size of the polymeric gallium species was estimated by measuring the increase in the basal (d₀₀₁) spacing of a montmorillonite upon intercalation. The hydrated height of the gallium polymer in its orientation relative to the phyllosilicate sheets was found to be approximately 9.4 Å, which is about 5.6% larger than the size of the Al₁₃ cationic unit, measured by the same method. This compares well with geometric calculations which show that a Ga₁₃ cationic species would be expected to be about 5.7% larger than the analogous aluminium species. These results suggest strongly that a [GaO₄Ga₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ cation forms during the hydrolysis of gallium(III) solutions at a pH range of approximately 3–4. The reason why this species has not been previously reported may be related to the fact that it appears to be much less stable in solution than the analogous aluminium species, as revealed by n.m.r. evidence.