Modeling small aluminum chlorohydrate polymers

Despite many experimental studies, the structure of aluminum chlorohydrate system is not well understood due to its complexity. Using a combination of Car Parrinello molecular dynamics and ab initio methods, we conclusively determine the structures of aluminum chlorohydrate monomer, dimer, trimer, and hexamer species. Contrary to the common assumption that the Al coordination shell in these compounds consists of OH groups and H₂O molecules only, we find that Cl^- ion incorporation in the octahedral structure of aluminum chlorohydrate monomer, dimer, and trimer increases their stability in the gas phase. The hexamer gas-phase structure is predicted to be built from both penta- and hexacoordinated Al³⁺ ions. Gas-phase optimized dimer and hexamer complexes are found to exhibit stable behavior in water solutions in the course of 7-8 ps of a Car Parrinello molecular dynamics run.