Additive polarizabilities of halides in ionic liquids and organic solvents.

The design of room-temperature ionic liquids featuring high refractive indices is desirable for a number of applications. Introducing strongly polarizable (poly)halides as anions is a promising route to increase the polarizability of an ionic liquid and thus the refractive index. Based on the experimental refractive indices and mass densities of imidazolium ionic liquids, additive atomic polarizabilities and volumes for chlorine, bromine, and iodine are determined. In addition, atomic polarizabilities and volumes for halide atoms in organic solvents are calculated and compared to ionic liquids. We find that especially iodine behaves differently in anions than in neutral or cationic species. A quantum-mechanical calculation of molecular and atomic polarizabilities complements and enhances the designed regression analysis. The gained insights into halide polarizability and volume are deployed to predict the refractive index of arbitrary ionic liquids.