Mechanochemical synthesis of the [Al13O4(OH)24(H2O)12]7+ Keggin ion

In this study, we demonstrate the synthesis of the [Al13O4(OH)24(H2O)12]7+ Keggin ε-Al13 ion by a mechanochemical reaction between [Al(H2O)6]Cl3 and (NH4)2CO3 reactants. Five grams of the starting mixture corresponding to a molar ratio of (NH4)2CO3/[Al(H2O)6]Cl3 = 0.45:2, 1:2, 1.5:2, 2:2, 2.25:2, 2.55:2 and 3:2 was milled for 5 min. The existence of ε-Al13 was observed at molar ratios of (NH4)2CO3/[Al(H2O)6]Cl3 = 2:2 and higher. Our results show that more than 50% mass of Al from a starting [Al(H2O)6]Cl3 was bonded to the polymeric [Al13O4(OH)24(H2O)12]7+ ionic form at a molar ratio of 2.55:2.