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.