The energetics of isomerisation in Keggin-series aluminate cations

摘要

Electronic-structure calculations show that the ε-isomer of the polyoxoaluminate ion in the Keggin structure [AlO_4-(Al(OH)_2-(H_2O))_(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 [Al_2O_8Al_(28)(OH)_(56)(H_2O)_(26)]~(18+) ion are discussed.