A route to a Keggin-Type alpha-[((XO4)-O-III)Mo12O35(OH)](4-) anion through an Anderson-type [X-III(OH)(6)Mo6O18](3-) anion: X = Ga

From an aqueous Mo-VI-Ga-III-HCl system, a colourless complex was isolated as a K+ salt, which consists of a hexaprotonated Anderson-type [Ga(OH)(6)Mo6O18](3-) anion. A yellow complex became kinetically stable by the presence of CH3CN at concentrations of 30-40% (v/v). The X-ray structural analysis revealed that the yellow (NPr4n)(4)[(GaO4)Mo12O35(OH)]crystal contains an alpha-Keggin structure and the oxygen atom at an edge-shared contact is protonated. The formation conditions of the Keggin complex were elucidated in relation to those of the Anderson complex by a combined Ga-71 NMR and voltammetric study. Evidence was obtained of a spontaneous conversion of [Ga(OH)(6)Mo6O18](3-) to [(GaO4)Mo12O35(OH)](4-) in the Mo-VI-Ga-III system.