Simple ionic liquids have long been held to be designer solvents, based upon the ability to independently vary their cations and anions. The formation of mixtures of ionic liquids increases this synthetic flexibility. We review the available literature of these ionic liquid mixtures to identify how their properties change and the possibility for their application.

The polarities of a wide range of ionic liquids have been determined using the Kamlet-Taft empirical polarity scales α, β and π*, with the dye set Reichardt's Dye, N,N-diethyl-4-nitroaniline and 4-nitroaniline. These have been compared to measurements of these parameters with different dye sets and to different polarity scales. The results emphasise the importance of recognising the role that the nature of the solute plays in determining these scales. It is particularly noted that polarity scales based upon charged solutes can give very different values for the polarity of ionic liquids compared to those based upon neutral probes. Finally, the effects of commonplace impurities in ionic liquids are reported.

We have studied the structure of two ionic liquids confined between negatively charged mica sheets. Both liquids exhibit interfacial layering, however the repeat distance is dramatically different for the two liquids. Our results suggest a transition from alternating cation-anion monolayers to tail-to-tail cation bilayers when the length of the cation hydrocarbon chain is increased.

14/08/12 MEB. Accepted version, embargo elapsed (jun 2012), OK to publis

A comprehensive study of ionic liquid mixtures reveals a remarkable adhesion to ideal mixing laws, with some consistent exceptions.

A range of methods for the computational prediction of experimentally derived α and β Kamlet-Taft parameters, indicators of hydrogen bond (H-bond) acidity and basicity for ionic liquids (ILs) have been explored. Most usefully, a good correlation has been established between several simple and easily computed quantities which allow for a "quick bench-top" evaluation. More accurate, but also more sophisticated methods employing TD-DFT calculations involving the Kamlet-Taft dyes have been examined and evaluated. Importantly, these techniques open up the opportunity for pre-screening and a priori prediction of properties for ILs not yet synthesised. A key fundamental insight into IL H-bonds has been the determination of an estimate for the energy associated with replacing both neutral molecules in a H-bond with ionic molecules, thus forming the "doubly ionic" H-bond found in ILs.

In this paper we use ab initio theoretical methods in combination with experimental studies to investigate ion-pairs of the ionic liquid (IL) 1-methyl-3-pentamethyldisiloxymethylimidazolium chloride [(SiOSi)C(1)C(1)im]Cl, in order to deepen our understanding of the effects of functionalisation on an IL. In addition, we focus on the effect of the siloxy group on the viscosity. We establish that the ion-pairing energies of [(SiOSi)C(1)C(1)im]Cl are similar to those of 1-butyl-3-methylimidazolium chloride [C(4)C(1)im]Cl, because the anion interacts primarily with the imidazolium ring. A large range of ion-pair structural configurations is possible with different anion positions and chain orientations, contributing to a significant entropy. A H-bonded network forms, however the siloxy chain can shield the Cl(-) or key C-H sites thus introducing defects. Despite a significant increase in mass relative to [C(4)C(1)im](+), the combined barriers to rotation within the substituent chain are substantially reduced in [(SiOSi)C(1)C(1)im](+), this is primarily due to the flexibility of the siloxane linkage, and free rotation of the Si-Me methyl groups. The most important effect is a coupling of rotational motions within the chain which leads to dynamic inter-conversion of cation conformers, and facilitates movement of the anion around the cation, these will contribute to enhanced transport properties and a reduced viscosity. In addition, a longer charge arm is expected to enhance rotational and rotational-translational coupling in electric fields. Thus, for [(SiOSi)C(1)C(1)im]Cl ion-pair association is very similar to that of [C(4)C(1)im]Cl, but "dynamic" properties relating to torsional motion, a dynamic H-bonded network, and cation response to an external electric field are enhanced.

Tri‐salts added: Pt on alumina catalysts can be used for converting methanol and water into hydrogen and carbon dioxide (see picture), for applications such as hydrogen storage. Both the activity and selectivity could be enhanced by coating these materials with a thin layer of a molten salt mixture of Li/K/Cs acetate. Potassium doping was identified by DRIFTS measurements to be an important factor for the boost in catalyst performance.