Solvation Structure of Ag ⁺ in 1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquid: Evidence for Linear N -Bound Coordination

High Resolution Image Download MS PowerPoint Slide The coordination environment of the Ag + ion in the 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C 4 mim][Tf 2 N]) ionic liquid (IL) was investigated through a combined experimental and theoretical approach including Raman and Fourier transform-infrared (FT-IR) spectroscopy, density functional theory (DFT) calculations, and X-ray absorption spectroscopy. Raman spectra in the 720–780 cm –1 region show the progressive conversion of “free” to coordinated [Tf 2 N] − anions upon addition of the silver salt to [C 4 mim][Tf 2 N], and quantitative analysis indicates an average coordination number of approximately two anions per Ag + ion. DFT calculations on the possible coordination isomers of the [Ag(Tf 2 N) 2 ] − complex reveal that the most stable species consists of two monodentate [Tf 2 N] − ligands bound to the Ag + cation through the central nitrogen atom, in agreement with the characteristic shifts observed in the experimental FT-IR spectra. Extended X-ray absorption fine structure analysis supports the presence of a well-defined first coordination shell featuring two Ag–N interactions at 2.23(2) Å arranged in an almost linear N–Ag–N geometry. Overall, the combined results establish a predominantly linear, N -bound solvation motif for Ag + in [C 4 mim][Tf 2 N]. This behavior contrasts with the coordination observed in other ILs and highlights the strong influence of the anion on metal ion solvation in these media.