CompChem and NMR Probing Ionic Liquids

Room temperature ionic liquids (RTILs) are salts of organic cations and, most often, inorganic anions. Their most significant difference from inorganic salts is their very much lower melting temperature, which together with their low vapor pressure, high thermal stability, and electrical conductivity make them unique both as neat liquids and as solvents. The high functionality of RTILs in a wide range of applications from Chemistry to Engineering is a result of their tunable interplay of intermolecular interactions from weak Van der Waals to strong Coulombic, in combination of being liquids at/close-to room temperature. The highly complex landscape of interactions of these organic-inorganic structures makes it challenging to study them experimentally and using computer modeling. The combination of experimental and computational techniques is thus of great importance to obtain reliable computational models of RTILs and insightful interpretation of experimental data. In this Chapter, we wish to show the readers how the combination of powerful techniques such as Nuclear Magnetic Resonance (NMR) spectroscopy and Molecular Dynamics (MD) simulations and Quantum Chemistry can be successfully used to provide a detailed and reliable picture of the structure and dynamics of RTILs. Structural information obtained from measurements of NMR chemical shift and nuclear Overhauser effect (NOE) effects can be fully interpreted from radial, spatial, and population distribution functions calculated in simulations. Dynamical information can be obtained from NMR relaxation measurements and interpreted using the information provided by MD simulations. This is true for all types of molecular systems. However, in the case of RTILs, both in experiments and in modeling we often need to go beyond standard approaches.