Insights Ionic Liquids

Germanium In situ STM studies on Ge electrodeposition on gold from an ionic liquid have quite recently been started at our institute [59, 60]. In these studies we used dry [BMIM][PF<3] as a solvent and dissolved Gel4 at estimated concentrations of 0.1-1 mmol 1 the substrate being Au(lll). This ionic liquid has, in its dry state, an electrochemical window of a little more than 4 V on gold, and the bulk deposition of Ge started several hundreds of mV positive from the solvent decomposition. Furthermore, distinct underpotential phenomena were observed. Some insight into the nanoscale processes at the electrode surface is given in Section 6.2.2.3. 

Furthermore, it is far beyond the scope of this chapter to provide any detailed insight into the materials science aspects of ionic liquids. However, it should be clearly stated that at least some understanding of the ionic liquid material is a prerequisite for its successful use as a catalyst layer in hydrogenation reactions. Therefore, the interested reader is strongly encouraged to explore the more specialized literature [39]. 

Bhargava, B.L., and Balasubramanian, S., Insights into the structure and dynamics of a room-temperature ionic liquid Ab initio molecular dynamics simulation studies of l-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PFj]) and the [bmim][PFj]-C02 mixture, /. Phys. Chem. B, 111, 4477-4487, 2007. 

H NMR studies gave insights into the stabilization of nanoclusters of iridium in imidazolium-type ionic liquids.30 It has been clearly established by H/D scrambling under a D2 atmosphere that NHCs are involved in this stabilization. 

The goal of this chapter is to compile existing knowledge on the behavior of ionic liquids and their influence on solvation and chemical reactivity. The intent is not to list reactions and their outcomes, but rather to review the results of studies that offer physical insight into the microscopic environment of ILs and their interaction with solute species. While many excellent reviews of ILs have been written [1, 4, 23, 30, 38 -0], this chapter is distinct in its attempt to identify the basic physical principles relevant to solvation in ILs. 

As was shown in Chapter 4, elemental tantalum can be electrodeposited in the water- and air-stable ionic liquid [Pyi,4] TFSA at 200°C using TaFs as a source of tantalum [ 15,16]. The quality of the deposit was found to be improved upon addition of LiF to the deposition bath. At room temperature only ultrathin tantalum layers can be deposited as the element. The electrodeposition of tantalum was investigated by in situ STM to gain insight into the electrodeposition process. 

The particular case of mixtures of ionic liquids with aromatic compounds has been studied by different authors and methods [38 41] and has provided several insights on the nature of these mixtures and on the interactions therein. 

However, despite all these similarities we should not forget that it is possible to optimize the catalytically active center in ionic liquids by molecular synthesis and ligand design, which is of course much easier and more efficient than to synthesize highly defined solid surfaces. Another very important difference - that should in particular be treated in this sub-section - is the possibility to analyze the active catalyst in an ionic liquid in a much easier and often more insightful way than this is possible for the surfaces of heterogeneous catalysts. In principle, this important advantage should enable more rational catalyst development and thus much quicker catalyst optimization times. 

---