Assessment of an effective quasirelativistic methodology designed to study astatine chemistry in aqueous solution

Abstract

A cost-effective computational methodology designed to study astatine (At) chemistry in aqueous solution has been established. It is based on two-component spin–orbit density functional theory calculations and solvation calculations using the conductor-like polarizable continuum model in conjunction with specific astatine cavities. Theoretical calculations are confronted with experimental data measured for complexation reactions between metallic forms of astatine (At⁺ and AtO⁺) and inorganic ligands (Cl⁻, Br⁻ and SCN⁻). For each reaction, both 1 ∶ 1 and 1 ∶ 2 complexes are evidenced. The experimental trends regarding the thermodynamic constants (K) can be reproduced qualitatively and quantitatively. The mean signed error on computed Log K values is −0.4, which corresponds to a mean signed error smaller than 1 kcal mol⁻¹ on free energies of reaction. Theoretical investigations show that the reactivity of cationic species of astatine is highly sensitive to spin–orbit coupling and solvent effects. At the moment, the presented computational methodology appears to be the only tool to gain an insight into astatine chemistry at a molecular level.