A Correlation for Establishing Solvolysis Rates of Aqueous Al(III) Complexes: A Possible Strategy for Colloids and Nanoparticles

Abstract

We here examine whether rates of solvolysis for a range of aluminum complexes can be predicted semiempirically by correlating calculated values of Al–O bond lengths with rate coefficients. We focus on a series of mono- and bis-ligated aqueous aluminum monomers and three ε-Keggin-like aluminum polyoxocations, and we make no attempt to simulate transition states. The Al–O bond lengths were calculated by performing ab initio geometry optimizations using the polarizable-continuum model to estimate solvation effects. Both Hartree–Fock and density functional methods (B3LYP) were tested using several basis sets up to 6-31+G(d). We find a strong correlation between rate coefficients for mono-ligated aluminum monomers and bond lengths to hydration waters. We cannot extrapolate the correlation, however, to large ε-Keggin-like multimers or to bis-ligated complexes, which suggests that the activated equilibrium for exchange of a water molecule in these molecules is different than that in the simple monomers.