Résumé
Understanding supramolecular organization in ionic liquids is essential for controlling their physicochemical properties and extraction performance. Here, we combine small-angle X-ray scattering (SAXS) experiments with molecular dynamics simulations to elucidate the structure of ionic liquids composed of trioctylammonium (TOAH+) cations and bis(trifluoromethanesulfonyl)imide (NTf2-) and sulfate (SO42-) anions across a wide range of compositions. The molecular model is validated as it reproduces experimental densities and SAXS intensities adequately. The calculated SAXS spectra accurately reproduce the positions of the three characteristic peaks observed experimentally at approximately 4, 8, and 14 nm–1. Decomposition of the SAXS signal into pairwise contributions reveals that the two lower-q peaks originate primarily from anion–anion correlations, whereas the highest-q peak arises from correlations between the carbon chains of the cations. Analysis of the corresponding radial distribution functions reveals a long-range structural organization in which anions are systematically separated by at least one cation, forming an anion-driven grid-like framework reminiscent of a crystal structure. These correlations indicate the presence of a persistent intermediate-range order that organizes the liquid into an anion-driven structural framework. This work provides a molecular-level interpretation of SAXS features in mixed-anion ionic liquids and reveals how subtle changes in anion identity govern supramolecular ordering.