Structural characterization of ionic liquids by X-ray absorption spectroscopy

In this chapter we will illustrate the advantages of X-Ray absorption spectroscopy (XAS) in the structural investigation of ionic liquids (ILs). The combination of a large range of organic cation and anion pairs makes possible to design an enormous number of ILs with specific properties. The characterization of structures in solution is usually elusive and very difficult to be obtained from the standard experimental techniques. With regards to studies of dilute solutions XAS spectroscopy is the structural probe of choice; due to its intrinsic chemical specificity and short range sensitivity this technique measures a less complex correlation function as compared to X-Ray and neutron diffraction that contains very accurate structural information on the short-range distances. This technique can be applied both to the solid and liquid state thus allowing the investigation of ILs in both aggregation states.