title: Imidazolium 2-substituted 4,5-dicyanoimidazolate ionic liquids: synthesis, crystal structures and structure-thermal property relationships.
abstract: Thirty six novel ionic liquids (ILs) with 1-butyl-3-methylimidazolium and 3-methyl-1-octylimidazolium cations paired with 2-substitited 4,5-dicyanoimidazolate anions (substituent at C2 = chloro, bromo, methoxy, vinyl, amino, methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl and phenyl) have been synthesized and characterized by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and single-crystal X-ray crystallography. The effects of cation and anion type and structure on the thermal properties of the resulting ionic liquids, including several room temperature ionic liquids (RTILs) are examined and discussed. ILs exhibited large liquid and crystallization ranges and formed glasses on cooling with glass transition temperatures in the range of -22 to -68 °C. The effects of alkyl substituents of the imidazolate anion reflected the crystallization, melting points and thermal decomposition of the ILs. The Coulombic packing force, van der Waals forces and size of the anions can be considered for altering the thermal transitions. Three crystal structures of the ILs were determined and the effects of changes to the cations and anions on the packing of the structure were investigated.
authors.affiliation: Insitut für Chemie, Anorganische Chemie, Universität Potsdam, Karl-Liebknecht-Straße 26, 14476 Potsdam (Germany). smondal@uni-potsdam.de.
authors.forename: Suvendu Sekhar
authors.initials: SS
authors.lastname: Mondal
authors.forename: Holger
authors.initials: H
authors.lastname: Müller
authors.forename: Matthias
authors.initials: M
authors.lastname: Junginger
authors.forename: Alexandra
authors.initials: A
authors.lastname: Kelling
authors.forename: Uwe
authors.initials: U
authors.lastname: Schilde
authors.forename: Veronika
authors.initials: V
authors.lastname: Strehmel
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Holdt
keywords: crystal structures; imidazole; ion exchange; ionic liquids; pi-pi stacking