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

Abstract

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 [RuCl 2 (p-cymene)P(C 8 H 17 ) 3 ] in perdeuterated 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide (d 11 -[C 2 mim][Tf 2 N]). 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.

Exploring the interfacial behavior of ruthenium complexes in ionic liquids: implications for supported ionic liquid phase catalysts

“…4 Previous studies have indicated that the nature of the ligands influence the concentration profile of the catalyst complex in solution, which may range from homogeneous distribution to surface enrichment or depletion at the interface. [5][6][7][8][9][10][11][12][13] If the catalyst tends to accumulate near the gas/IL interface, the total process is expected to be more efficient. Therefore, it is crucial to determine the factors influencing the surface enrichment of catalysts in ILs, a matter that has not been fully elucidated yet.…”

Understanding the Buoy Effect of Surface‐Enriched Pt Complexes in Ionic Liquids: A Combined ARXPS and Pendant Drop Study**

“…A detailed study by the groups of J. M. Slattery and T. K. Minton revealed enrichment of a Ru catalyst at the IL/vacuum interface in [C 2 C 1 Im][Tf 2 N] by reactive‐atom scattering (RAS), time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) and X‐ray photoelectron spectroscopy (XPS) [13] . The ligand system featured the non‐polar phosphine ligand P(C 8 H 17 ) 3 , which is proposed to induce preferential population of the complex at the outer surface due to the aliphatic octyl chain [13] . The importance of the ligands’ nature on the surface behavior of organometallic complexes was also investigated by our group over the past years [14] .…”

“…[13] The ligand system featured the non-polar phosphine ligand P(C 8 H 17 ) 3 , which is proposed to induce preferential population of the complex at the outer surface due to the aliphatic octyl chain. [13] The importance of the ligands' nature on the surface behavior of organometallic complexes was also investigated by our group over the past years. [14] Recently, we demonstrated that the concentration profile of Pt complexes can be deliberately altered by manipulating the ligand system.…”

“…While the interfacial properties of neat ILs and mixtures of ILs have been addressed quite thoroughly in the past decades and continue to attract intense interest, [1a,12] literature on IL‐based catalyst solutions is rather scarce. A detailed study by the groups of J. M. Slattery and T. K. Minton revealed enrichment of a Ru catalyst at the IL/vacuum interface in [C 2 C 1 Im][Tf 2 N] by reactive‐atom scattering (RAS), time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) and X‐ray photoelectron spectroscopy (XPS) [13] . The ligand system featured the non‐polar phosphine ligand P(C 8 H 17 ) 3 , which is proposed to induce preferential population of the complex at the outer surface due to the aliphatic octyl chain [13] .…”

Small-angle neutron scattering from mixtures of long- and short-chain 3-alkyl-1-methyl imidazolium bistriflimides

“…As part of a study aimed initially at understanding the properties of imidazolium ILs at the gas-liquid interface using reactive atom scattering, 20,[26][27][28][29][30][31][32][33][34][35][36] a series of mixtures was prepared with the composition [C 12 mim] x [C 2 mim] 1Àx [Tf 2 N] (Fig. 1).…”