Temperature and angle resolved XPS study of BMIm Cl and BMIm FeCl4

Ionic liquids (ILs) have progressively acquired a central position in chemical and material sciences landscapes due to their peculiar physical and solvation properties. Thanks to their metal-complexing ability as well as wide thermal stability and the capability to be easily reused, ILs constitute ideal candidates for applications in metal-catalyzed reactions. However, to exploit their full potential as solvents in heterogeneous catalysis, it is essential to achieve a deeper knowledge on the phenomena that govern both ILs's surface physical chemistry and chemical composition. With the aim of shedding some light on these aspects, we used X-ray photoelectron spectroscopy in angle-resolved mode, to analyze the surface of BMIm Cl and BMIm FeCl4 at different probing depths. Our results show that iron species are located nearly the liquid/vacuum interface, immediately under the hydrophobic layer constituted by the aliphatic chains of the imidazolium rings. The presence of iron ions also affects the composition of the outermost part of the liquid/vacuum interface which clearly differs from the one constituted by the parent BMIm Cl.