Theoretical investigation of the dissociative interchange (Id) mechanism for water exchange on magnesium(II) in aqueous solution

A dissociative (D) and a solvent-assisted dissociative interchange (Id) water-exchange pathways for magnesium(II) in aqueous solution were simulated with density functional theory calculations. The D mechanism of Mg ( H 2 O ) 6 2 + includes a five-coordinated intermediate, while the Id water-exchange pathway of Mg ( H 2 O ) 6 2 + proceeds with the assistance of a solvent water molecule, which supports the experimental assignment of the reaction mechanism. The intrinsic activation volume was used to differentiate between Id and Ia mechanisms despite of the exclusion of the contribution of transmission coefficient. The calculated intrinsic activation volume for the Id mechanism is consistent with the experimental data, and is closer to the experimental data than that for D mechanism. The Id mechanism is suggested as the dominate water-exchange pathway of Mg ( H 2 O ) 6 2 + depending on the intrinsic activation volume with the assistance of the activation entropy. The calculations also showed that the influences of the explicit and bulk waters on energy barriers for D and Id mechanisms are obviously different.