title: Association of ionic liquids in solution: a combined dielectric and conductivity study of [bmim][Cl] in water and in acetonitrile.
abstract: Ion association of the ionic liquid [bmim][Cl] in acetonitrile and in water was studied by dielectric spectroscopy for salt concentrations c ≤ 1.3 M at 298.15 K and by measurement of molar electrical conductivities, Λ, of dilute solutions (c ≤ 0.006 M) in the temperature range 273.15 ≲ T/K ≤ 313.15. Whilst acetonitrile solutions of [bmim][Cl] exhibit moderate ion pairing, with an association constant of K°(A) ≈ 60 M(-1) and increasing with temperature, [bmim][Cl] is only weakly associated in water (K°(A) ≈ 6 M(-1)) and ion pairing decreases with rising temperature. Only contact ion pairs were detected in both solvents. Standard-state enthalpy, entropy and heat capacity changes of ion association were derived, as well as the activation enthalpy of charge transport and the limiting conductivity of the cation, λ(∞) ([bmim](+)). These data, in conjunction with effective solvation numbers obtained from the dielectric spectra, suggest that the solvation of [bmim](+) is much weaker in water than in acetonitrile.
authors: Faculty of Chemistry and Chemical Technology, University of Ljubljana, SI-1000 Ljubljana, Slovenia. Marija.Bester@fkkt.uni-lj.si
authors: Marija
authors: M
authors: Bešter-Rogač
authors: Alexander
authors: A
authors: Stoppa
authors: Johannes
authors: J
authors: Hunger
authors: Glenn
authors: G
authors: Hefter
authors: Richard
authors: R
authors: Buchner
mesh_terms: D000097:Acetonitriles / Q000737:chemistry*; D004553:Electric Conductivity; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D012996:Solutions; D014867:Water / Q000737:chemistry*
chemical_list: D000097:Acetonitriles; D007093:Imidazoles; D052578:Ionic Liquids; D012996:Solutions; D014867:Water; C518739:1-ethyl-3-methylimidazolium; C032159:acetonitrile