The solvation of Al3+ and its hydrolyzed species in water clusters has been carried out by means of ab initio molecular dynamics simulations.
The hexa-hydrate Al(H2O)63+ ion is a stable complex in the finite temperature cluster simulation of one aluminum ion and 16 waters.
The approximate dipole moments of strongly polarized hydrated water molecules in the first solvation shell of Al(H2O)63+ were found to be about 5 Debye.
The deprotonated Al(H2O)2(OH)4- complex evolves into a tetra-coordinated Al(OH)4- aluminate ion with two water molecules in the second solvation shell forming hydrogen bonds to the hydroxyl groups.
The main geometrical parameters for the lowest energy structures of hexa-hydrate and aluminate ions obtained using simulated annealing are in a good agreement with known MP2 results and experimental data. The connection between Al3+ coordination and its hydrolysis is discussed.
Ab initio molecular dynamics of aluminum solvation
by Mark I. Lubin and John H. Weare, UCSD