Understanding Ionic Liquids at the Molecular Level: Facts, Problems, and Controversies

Abstract

Ionic liquids (ILs) are organic salts with melting points near room temperature (or by convention below 100 degrees C). Recently, their unique materials and solvent properties and the growing interest in a sustainable, "green" chemistry has led to an amazing increase in interest in such salts. A huge number of potential cation and anion families and their many substitution patterns allows the desired properties for specific applications to be selected. Because it is impossible to experimentally investigate even a small fraction of the potential cation-anion combinations, a molecular-based understanding of their properties is crucial. However, the unusual complexity of their intermolecular interactions renders molecular-based interpretations difficult, and gives rise to many controversies, speculations, and even myths about the properties that ILs allegedly possess. Herein the current knowledge about the molecular foundations of IL behavior is discussed.

Do H-bonds explain strong ion aggregation in ethylammonium nitrate + acetonitrile mixtures?

“…To understand interactions in such systems knowledge of their structure and dynamics is essential. Up to now, most publications dealing with the dynamics of ILs and their mixtures with non-ionic compounds have focused on salts with 1-alkyl-3-methylimidazolium cations [9][10][11][12][13] but only little is known about PIL-containing systems. 14,15 In this contribution we present a first systematic study of the cooperative dynamics of EAN + dipolar aprotic solvent mixtures.…”

Low-frequency Raman spectra and fragility of imidazolium ionic liquids

“…11,12 Ionic liquids contain relatively large asymmetric organic ions and they are usually good glass-formers with T g ϳ 190 K. These materials attract attention as alternative solvents or electrolytes for electrochemical devices; therefore, fragility is an important issue because lower T g does not necessarily imply higher fluidity at room temperature. 2 The short-time intermolecular dynamics of ionic liquids has been the subject of many investigations by optical Kerr effect ͑OKE͒ spectroscopy.…”

Checkerboard Self-Patterning of an Ionic Liquid Film on Mercury

“…The intense scientific interest in RTILs stems from their complex combination of interactions, van der Waals, Coulomb, dipole, and hydrogen bonding, rarely occurring simultaneously in other materials [5,6]. Being infiniteconcentration ionic "solutions", RTILs are strongly correlated systems, going beyond the validity regime of the Poisson-Boltzman equation, and the Gouy-Chapman and Stern models of the electric double layer [7], and thus allowing insight into this scarcely studied regime.…”