A route to a Keggin-Type α-[(XIIIO4)Mo12O35(OH)]4− anion through an Anderson-type [XIII(OH)6Mo6O18]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)Mo(6)O(18)](3-) anion. A yellow complex became kinetically stable by the presence of CH(3)CN at concentrations of 30-40% (v/v). The X-ray structural analysis revealed that the yellow (NPr(n)(4))(4)[(GaO(4))Mo(12)O(35)(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 (71)Ga NMR and voltammetric study. Evidence was obtained of a spontaneous conversion of [Ga(OH)(6)Mo(6)O(18)](3-) to [(GaO(4))Mo(12)O(35)(OH)](4-) in the Mo(VI)-Ga(III) system.