The Buoy Effect: Surface Enrichment of a Pt Complex in IL Solution by Ligand Design

Abstract

The targeted enrichment of a Pt complex with an ionic liquid (IL)‐derived ligand system in IL solution is demonstrated by using angle‐resolved X‐ray photoelectron spectroscopy. When the ligand system is complemented with fluorinated side chains, the complex accumulates strongly at the IL/gas interface, while in an equivalent solution of a complex without these substituents no such effect could be observed. This buoy‐like behavior induces strong population of the complex at the outermost molecular layer close to surface saturation, which was studied over a range from 5 to 30 %mol. The surface enrichment was found to be most efficient at the lowest concentration, which is particularly favorable for catalytic applications such as supported ionic‐liquid‐phase (SILP) catalysis.

Evolution of Surface Tension and Hansen Parameters of a Homologous Series of Imidazolium-Based Ionic Liquids

“…For example, it has been shown that fluorinated alkyl chains accumulate at the gas−liquid interface to minimize the surface tension. 75,76 Similarly, the length of the alkyl chain as well as the anion size and the IL polarity affect the surface tension and molecular arrangement at the interface. 18,44,77−80 In the following, we study the evolution of surface 45,51,78 By increasing the alkyl chain length, the IL surface is more and more dominated by a nonpolar layer of hydrophobic alkyl chains, which are located above an ionic sublayer mainly consisting of charged moieties (imidazolium cations, anions).…”

“…Molecules at the interface will orient in a thermodynamically preferred position to reduce the interfacial energies. For example, it has been shown that fluorinated alkyl chains accumulate at the gas–liquid interface to minimize the surface tension. , Similarly, the length of the alkyl chain as well as the anion size and the IL polarity affect the surface tension and molecular arrangement at the interface. ,,− In the following, we study the evolution of surface tension and Hansen parameters as a function of the cation structure and anion size, first for [C n C 1 Im]­[A] ILs. Table summarizes all determined values of the surface tension γ, their dispersive and polar contributions γ d and γ p , as well as their HSPs (δ d , δ p , and δ h ).…”

Structure and Surface Behavior of Rh Complexes in Ionic Liquids Studied Using Angle-Resolved X-ray Photoelectron Spectroscopy

“…By performing angle-resolved XPS (ARXPS), a detailed structural picture of the IL/vacuum interface can be obtained, because in organic matter, the information depth (ID) decreases from 6-9 nm at 0 • (normal electron emission), to 1.0-1.5 nm at an 80 • (grazing electron emission) angle [84]. With ARXPS, preferential surface orientations and configurations, as well as the enrichment and depletion effects, are accessible [24,60,[67][68][69][70][71][72][85][86][87][88][89], which has successfully been shown for IL-based catalyst solutions [14,[73][74][75][76].…”

“…X-ray photoelectron spectroscopy (XPS) has shown to be a particularly powerful tool for the analysis of the interface-near region of neat ILs [49][50][51][60][61][62][63][64][65][66], IL mixtures [67][68][69][70][71][72], and IL solutions [14,[73][74][75][76][77][78][79]. With special interest in catalysis, significant effort has been dedicated to elucidate the nature and the interfacial behavior of organometallic complexes in IL solutions over recent years.…”

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. 5–13 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.…”