Anomalous Water Penetration in Al3+ Dissolution

Abstract

The physicochemical characterization of trivalent ions is limited due to a lack of accurate force fields. By leveraging the latest machine learning force field to model aqueous AlCl₃, we discover that upon dissolution of Al³⁺, water molecules beyond the second hydration shell are involved in the hydration process. A combination of scissoring of coordinating water is followed by synchronized secondary motion of water in the second solvation shell due to hydrogen bonding. Consequently, the water beyond the second solvation penetrates through the second solvation shell and coordinates to the Al³⁺. Our study reveals a novel microscopic understanding of solvation dynamics for the trivalent ion.