On-Surface Metathesis of an Ionic Liquid on Ag(111)

We investigated the adsorption, surface enrichment, ion exchange, and on-surface metathesis of ultrathin mixed IL films on Ag(111). We stepwise deposited 0.5 ML of the protic IL diethylmethylammonium trifluoromethanesulfonate (dema]TfO]) and 1.0 ML of the aprotic IL 1-methyl-3-octylimidazolium hexafluorophosphate (C₈C₁Im]PF₆]) at around 90 K. Thereafter, the resulting layered frozen film was heated to 550 K, and the thermally induced phenomena were monitored in situ by angle-resolved X-ray photoelectron spectroscopy. Between 135 and 200 K, TfO]^? anions at the Ag(111) surface are exchanged by PF₆]^? anions and enriched together with C₈C₁Im]⁺ cations at the IL/vacuum interface. Upon further heating, dema]PF₆] and OMIm]PF₆] desorb selectively at ～235 and ～380 K, respectively. Hereby, a wetting layer of pure C₈C₁Im]TfO] is formed by on-surface metathesis at the IL/metal interface, which completely desorbs at ～480 K. For comparison, ion enrichment at the vacuum/IL interface was also studied in macroscopic IL mixtures, where no influence of the solid support is expected.