UC Davis

Electronic-structure calculations show that the ε-isomer of the polyoxoaluminate ion in the Keggin structure [AlO4-(Al(OH)2(H2O))12](7+) is the thermodynamically favoured one. Direct interconversion between the ε- and δ-isomers via cap rotation has a prohibitively high energy barrier in vacuo, suggesting that isomerisation in solution either proceeds via a dissolution-precipitation pathway, or that solvation and/or coordination to counterions reduces the barrier significantly. The implications for the formation of the [Al2O8Al28(OH)56(H2O)26](18+) ion are discussed.