Understanding and predicting the physical properties of ILs: (Monte Carlo augmented) Born-Fajans-Haber-Cycle approaches, a systematic temperature dependent experimental and theoretical investigation of the molecular and free volumes of solid and liquid ILs

• Applicants: Professor Dr. Thorsten Koslowski; Professor Dr. Ingo Krossing; Professor Dr. Sergey Verevkin
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2006 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 29468086

Ionic liquids (ILs) are currently receiving a great deal of attention due to their potential use in a wide range of applications. However, as the number of applications for these materials grows, we still know very little about the origins of their fundamental properties. Furthermore, there are currently very few quantitative methods to predict the properties of unknown salts. Trial and error methods must be used to design new ILs for particular applications, which limit the progress in this field. Thus, the ability to predict the properties of yet unknown ILs in a simple procedure, would allow ILs to fulfil their destiny as designer materials, which can be tailored to a specific application. In this context we have recently developed a simple, quantitative explanation of the relatively low melting temperatures of ILs (mp s). This model can be used to predict the mp s and dielectric constants of ILs with good accuracy using simple calculations and a minimum of experimental data. As such, this technique has the potential to be used by general chemists to help in the design of new ILs. In this proposal we describe how this model can be refined to improve the accuracy of its predictions as well as to solve problem cases for the method, e.g. by determining thermodynamic properties of ILs as well as solid-state structures of ambient temperature ionic liquids. Preliminary results suggest a simple relationship between the (thermochemical) molecular volume of an IL and the viscosity and conductivity of the salt. In the proposed project we will extend these correlations, both, on an experimental as well as theoretical basis. During our work on weakly coordinating anions we have discovered that the Li+ salts of fluorinated alkoxyaluminate anions [A1(ORF)4]- melt at relatively low temperatures. One of these salts has a melting point of 42-45 °C, which already classifies this material as an IL. ILs with Li+ as the cation (Li+-ionic liquids) are currently extremely rare, but have the potential for use as electrolytes in batteries and super capacitors and as Li+-ion catalysts for organic chemistry. During the proposed project we will develop the chemistry of Li+ salts of fluorinated alkoxyaluminate anions, and by changing the structure and functionality of the anion develop materials that are liquid at ambient temperatures. Moreover, we will investigate the structural features of the anion that lead to high Li+ mobility and availability for particular applications. We will be able to use the theoretical methods developed during the project to help in the design of Li+-ionic liquids and where necessary develop new models that are specific to this special type of IL.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1191: Ionic Liquids