Characterization of precipitates from the reactions between [Al13O4(OH)24(H2O)12]7+ polycations and [Mo7O24]6− polyoxometalate anions

The reactions between polycation [Al13O4(OH)24(H2O)12]7+ and polyoxometalate [Mo7O24]6− in aqueous solutions produced precipitates composed of [Al13O4(OH)24(H2O)12]7+, [Mo7O24]6− and [Al(OH)6Mo6O18]3− ions. Infrared and solid state 27Al-NMR spectroscopic data identified the individual polyions in these precipitates. The compositions of the precipitates, derived from the integrated intensity ratio of the 27Al-NMR peaks for the [Al13O4(OH)24(H2O)12]7+ and [Al(OH)6Mo6O18]3− and the Al/Mo ratios from ICP elemental analysis data, in addition to the charge balance considerations, reflect the composition of the reacting solutions. Depending on the composition, the [Al13O4(OH)24(H2O)12]7+ inside the precipitates can undergo oligomerization or polymerization reactions upon aging in contact with the mother liquor over a week, as evidenced by the solid-state 27Al-NMR data.