title: When Like Charged Ions Attract in Ionic Liquids: Controlling the Formation of Cationic Clusters by the Interaction Strength of the Counterions.
abstract: The properties of ionic liquids are described by a subtle balance between Coulomb interaction, hydrogen bonding, and dispersion forces. We show that lowering the attractive Coulomb interaction by choosing weakly coordinating anions leads to the formation of cationic clusters. These clusters of like-charged ions are stabilized by cooperative hydrogen bonding and controlled by the interaction potential of the anion. IR and NMR spectroscopy combined with computational methods are used to detect and characterize these unusual, counter-intuitively formed clusters. They can be only observed for weakly coordinating anions. When cationic clusters are formed, cyclic tetramers are particularly stable. Therein, cooperative hydrogen-bond attraction can compete with like-charge repulsion. We present a simple but effective spectroscopic scale for the possibility of like-charge attraction in ionic liquids, based on IR and NMR signatures.
authors.affiliation: Universität Rostock, Institut für Chemie, Abteilung für Physikalische Chemie, Dr.-Lorenz-Weg 1, 18059, Rostock, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Strate
authors.affiliation: Universität Rostock, Institut für Chemie, Abteilung für Physikalische Chemie, Dr.-Lorenz-Weg 1, 18059, Rostock, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Niemann
authors.affiliation: Leibniz-Institut für Katalyse an der, Universität Rostock e.V., Albert-Einstein-Strasse 29a, 18059, Rostock, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Michalik
authors.affiliation: Universität Rostock, Institut für Chemie, Abteilung für Physikalische Chemie, 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
keywords: DFT calculations; IR spectroscopy; hydrogen bonding; ionic liquids; like-charge interaction