Structure and dynamics of the aluminum chlorohydrate polymer Al₁₃O₄(OH)₂₄(H₂O)₁₂Cl₇

The Al₁₃ polymer, Al₁₃O₄(OH)₂₄(H₂O)₁₂Cl₇, is thought to be a major component of the aluminum chlorohydrate (ACH) polymer system. Although it plays important roles in various aluminum chlorohydrate applications, its structure is not well understood. We combine ab initio molecular dynamics simulations in both the gas-phase and aqueous solution, with small angle X-ray scattering experiments on a bulk ACH sample to determine the structure of Al₁₃-mer. We find that Al₁₃ entity is roughly spherical (∼10 Å diameter), with a central tetrahedral Al³⁺ ion surrounded by four shells consisting of O, OH and H₂O groups. Our ab initio molecular dynamics studies indicate that such a structure is stable on the picosecond time scale in an aqueous environment.