Probing a Ruthenium Coordination Complex at the Ionic Liquid–Vacuum Interface with Reactive-Atom Scattering, X‑ray Photoelectron Spectroscopy, and Time-of-Flight Secondary Ion Mass Spectrometry

The speciation, conformation, and reactivity of transition metal complexes at the gas–liquid interface are poorly understood, yet the potential is high for observing chemistry unique to this anisotropic interface and leveraging interfacial structure to control the state and environment of the complex. If transition metal complexes can be designed to populate a liquid–vacuum interface preferentially, then it may be possible to explore catalytic behavior by delivering reactants to the interface with a molecular beam and monitoring the scattering dynamics of reaction products to obtain detailed information on the reaction mechanism. In this initial experimental study, we have used reactive-atom scattering with a hyperthermal F-atom probe, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry to explore the interfacial composition and structure of a ∼2 mg/mL solution of [RuCl₂(p-cymene)­P­(C₈H₁₇)₃] in perdeuterated 1-ethyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide (d₁₁-[C₂mim]­[Tf₂N]). These data provide strong evidence that a Ru complex is present at the extreme liquid–vacuum interface with a number density that is higher than expected from the bulk concentration (2–3 vs 0.04%). The experimental data also provide information on the chemical nature and environment of the Ru complex that resides at or near the extreme liquid–vacuum interface.