Unraveling the Ag+ ion coordination and solvation thermodynamics in the 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid.

The solvation of the Ag+ ion in the 1-butyl-3-methylimidazolium tetrafluoroborate ([C 4 mim][BF 4 ]) ionic liquid (IL) has been studied by means of experimental and theoretical methods with the aim of elucidating the cation coordination structure and thermodynamic properties. Car-Parrinello molecular dynamics (CPMD) simulations showed that the Ag+ ion is coordinated by an average number of four [BF 4 ]− anions in a pseudo-tetrahedral geometry. A high configurational disorder of the first solvation sphere is found, where the anions can be found both in mono- and bidentate coordination mode around the Ag+ ion. Also, a solvational equilibrium is observed as due to [BF 4 ]− anion dissociation along the trajectory. The analysis of X-ray absorption spectroscopy data confirmed the picture provided by the CPMD simulation. Classical molecular dynamics simulations were carried out to obtain the single-ion solvation thermodynamic parameters. The negative water → IL free energy of transfer suggests that the Ag+ ion is more favorably solvated in the [C 4 mim][BF 4 ] IL than in water. This behavior is due to a balance between the enthalpic and entropic contributions, which allows to find a rationale to the strong solvation capabilities of BF 4 -based ILs towards Ag+. • The coordination environment and solvation thermodynamics of the Ag+ ion the [C 4 mim][BF 4 ] ionic liquid are analyzed. • CPMD simulations show that the Ag+ ion is coordinated by four [BF 4 ]− anions in a tetrahedral geometry. • XAS data confirm the local structure around the Ag+ ion and a high configurational disorder of the solvation sphere. • Ag+ ion is more favorably solvated in [C 4 mim][BF 4 ] than in water. [ABSTRACT FROM AUTHOR]