Density Functional Theory Studies on the Real and Apparent Water-Exchange Reaction Kinetics of Al3+ in Aqueous Solution

Abstract

The dissociative (D) mechanistic water-exchange kinetics of aquated Al3+ in aqueous solution is systematically studied using the density functional theory-quantum chemical cluster model (DFT-CM) method. The modeled pathways include dehydration of the hexacoordinated Al(H2O)63+ and successive hydration of the pentacoordinated Al(H2O)53+. For the hydration of Al(H2O)53+, the attacking pathways corresponding to the second-shell solvent water molecules at different sites are investigated. The gas phase-supermolecule-polarizable continuum model (GP-SM-PCM) is used to simulate the explicit and bulk solvation effects. The reactant, transition state, and product geometries of the modeled reaction pathways are optimized at the B3LYP/6-311+G(d,p) level of theory. The real and apparent water-exchange reaction mechanisms of Al3+ are analyzed based on the Gibbs free energy changes for the dehydration and hydration pathways. The possible ligand competition with the solvent water molecules in the formation of aqueous Al...