title: Imidazolium salt ion pairs in solution.
abstract: The formation, stabilisation and reactivity of contact ion pairs of non-protic imidazolium ionic liquids (ILs) in solution are conceptualized in light of selected experimental evidence as well theoretical calculations reported mainly in the last ten years. Electric conductivity, NMR, ESI-MS and IR data as well as theoretical calculations support not only the formation of contact ion pairs in solution, but also the presence of larger ionic and neutral aggregates even when dissolved in solvents with relatively high dielectric constants, such as acetonitrile and DMSO. The presence of larger imidazolium supramolecular aggregates is favoured at higher salt concentrations in solvents of low dielectric constant for ILs that contain shorter N-alkyl side chains associated with anions of low coordination ability. The stability and reactivity of neutral contact species are also dependent on the nature of the anion, imidazolium substituents, and are more abundant in ILs containing strong coordinating anions, in particular those that can form charge transfer complexes with the imidazolium cation. Finally, some ILs display reactivities as contact ion pairs rather than solvent-separated ions.
authors.affiliation: Institute of Chemistry, UFRGS, Av. Bento Gonçalves, 9500 Porto Alegre 91501-970 RS (Brazil).
authors.forename: Hubert K
authors.initials: HK
authors.lastname: Stassen
authors.affiliation: Physical and Theoretical Chemistry, University of Rostock, Dr.-Lorenz-Weg 1, 18059 Rostock (Germany).|Leibniz-Institut für Katalyse an der Universität Rostock e.V. Albert-Einstein-Strasse 29a, 18059 Rostock (Germany).
authors.forename: Ralf
authors.initials: R
authors.lastname: Ludwig
authors.affiliation: Physical and Theoretical Chemistry, University of Rostock, Dr.-Lorenz-Weg 1, 18059 Rostock (Germany).
authors.forename: Alexander
authors.initials: A
authors.lastname: Wulf
authors.affiliation: Institute of Chemistry, UFRGS, Av. Bento Gonçalves, 9500 Porto Alegre 91501-970 RS (Brazil). Jairton.dupont@ufrgs.br, jairton.dupont@nottingham.ac.uk.|School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD (UK). Jairton.dupont@ufrgs.br, jairton.dupont@nottingham.ac.uk.
authors.forename: Jairton
authors.initials: J
authors.lastname: Dupont
keywords: conductivity; imidazolium salts; ion pairs; ionic liquids; solutions