The structural parameters of Al(H2O)n3+ , n = 1-6(slide 2)
The filling out of the first solvation shell of aluminum cation by water molecules yields the gradual increase in the length of the coordination bond Al-O. At the same time, the average dipoles of the hydrated waters decrease by almost 20 %. This means that the coordination fluctuations in the first solvation shell of aluminum cation which are in turn effected by the second solvation shell dynamics can cause the increase in the polarization of the hydrated waters.
We have found that at n = 1, 2, 3 clusters had a planar structure, n = 4 cluster was a tetrahedral complex, and at n = 5, the structure Al(H2O)53+ was represented by square-based pyramid.
Ab initio molecular dynamics of aluminum solvation
by Mark I. Lubin and John H. Weare, UCSD