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Determination of LFER Descriptors of 30 Cations of Ionic Liquids—Progress in Understanding Their Molecular Interaction Potentials

Authors

  • Chul-Woong Cho,

    1. Zentrum für Umweltforschung und nachhaltige Technologien (UFT)—Centre for Environmental Research and Sustainable Technology, University of Bremen, Leobener Straße, 28359 Bremen (Germany), Fax: (+49) (0)421 2187643
    2. Freiburger Materialforschungszentrum FMF, University of Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg (Germany), Fax: (+49) (0)761 2036001
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  • Dr. Christian Jungnickel,

    1. Zentrum für Umweltforschung und nachhaltige Technologien (UFT)—Centre for Environmental Research and Sustainable Technology, University of Bremen, Leobener Straße, 28359 Bremen (Germany), Fax: (+49) (0)421 2187643
    2. Chemical Faculty, Gdańsk University of Technology ul. Narutowicza 11/12, 80-233 Gdańsk (Poland)
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  • Dr. Stefan Stolte,

    1. Zentrum für Umweltforschung und nachhaltige Technologien (UFT)—Centre for Environmental Research and Sustainable Technology, University of Bremen, Leobener Straße, 28359 Bremen (Germany), Fax: (+49) (0)421 2187643
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  • Dr. Ulrich Preiss,

    1. Freiburger Materialforschungszentrum FMF, University of Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg (Germany), Fax: (+49) (0)761 2036001
    2. Interdisciplinary Centre for Advanced Materials Simulation (ICAMS), Ruhr-Universität Bochum, Stiepeler Str. 129, 44801 Bochum (Germany)
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  • Dr. Jürgen Arning,

    1. Zentrum für Umweltforschung und nachhaltige Technologien (UFT)—Centre for Environmental Research and Sustainable Technology, University of Bremen, Leobener Straße, 28359 Bremen (Germany), Fax: (+49) (0)421 2187643
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  • Dr. Johannes Ranke,

    1. Zentrum für Umweltforschung und nachhaltige Technologien (UFT)—Centre for Environmental Research and Sustainable Technology, University of Bremen, Leobener Straße, 28359 Bremen (Germany), Fax: (+49) (0)421 2187643
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  • Prof. Ingo Krossing,

    Corresponding author
    1. Freiburger Materialforschungszentrum FMF, University of Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg (Germany), Fax: (+49) (0)761 2036001
    2. Institut für Anorganische und Analytische Chemie, University of Freiburg, Albertstraße 21, 79104 Freiburg (Germany)
    3. FRIAS Fellow of the Section Soft Matter Science
    • Freiburger Materialforschungszentrum FMF, University of Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg (Germany), Fax: (+49) (0)761 2036001
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  • Prof. Jorg Thöming

    Corresponding author
    1. Zentrum für Umweltforschung und nachhaltige Technologien (UFT)—Centre for Environmental Research and Sustainable Technology, University of Bremen, Leobener Straße, 28359 Bremen (Germany), Fax: (+49) (0)421 2187643
    • Zentrum für Umweltforschung und nachhaltige Technologien (UFT)—Centre for Environmental Research and Sustainable Technology, University of Bremen, Leobener Straße, 28359 Bremen (Germany), Fax: (+49) (0)421 2187643
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Abstract

In order to understand molecular interaction potentials of 30 cations of ionic liquids (ILs), the well-known linear free energy relationship concept (LFER) was applied. The LFER descriptors for the excess molar refractivity and the molar volume were calculated in silico and for hydrogen-bonding acidity and basicity, and the polarizability/dipolarity of IL cations were experimentally determined through high performance liquid chromatography (HPLC) measurements. For the study, three different columns (RP-select B, Cyan, and Diol) and buffered mobile phases, based on two organic solvents acetonitrile (ACN) and methanol (MeOH), were selectively combined to the HPLC separation systems RP-select B-ACN, RP-select B-MeOH, Cyan-MeOH, Diol-ACN, and Diol-MeOH. By measuring the retention factors of 45 neutral calibration compounds and calculating LFER descriptors of three cations in the HPLC systems, the system parameters, including an ionic z coefficient, were determined. Conversely, the LFER descriptors of 30 ionic liquid cations were determined, based on the parameters of five systems and their retention factors in the HPLC systems. The results showed that the type of head group, alkyl chain length and further substituents of the cation have a significant influence on the dipolarity/polarizability and the hydrogen-bonding acidity, and functionalized groups (hydroxyl, ether, and dimethylamino) lead to hydrogen-bonding basicity of the cation. The characterization of cationic LFER descriptors opens up the chance for a more quantitative understanding of molecular interaction potentials and physicochemical properties of ILs.

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