An Atomic-Scale Understanding of the Solution Chemistry of Antimony(V): Insights from First-Principles Molecular Dynamics Simulation.

In this study, the structure, hydrolysis, and complexation of Sb(V) in aqueous solution has been elucidated by using first-principles molecular dynamics (FPMD) simulations. The results show that both antimonic acid and its deprotonated form have an octahedral configuration, with average Sb-OH2 and Sb-OH distances of 2.25 and 2.05 Å, respectively. The computed pKa of [Sb(OH)5(OH2)] is 1.8, while [Sb(OH)6]- has an extremely high pKa. Consequently, [Sb(OH)6]- is the most dominant species of Sb(V) under common environmental conditions. A stable aqueous complex can form between [Sb(OH)6]- and common cations, and an Sb-Al bidentate complex has the largest dissociation free energy, followed by a Sb-Mg bidentate complex, indicating that they have significantly higher stabilities. For Na+ and Ca2+, their respective monodentate and bidentate complexes have similar dissociation free energies, indicating very close possibilities. These findings provide a comprehensive understanding of the solution chemistry of Sb(V) from a quantitative and microscopic perspective.