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When Like Charged Ions Attract in Ionic Liquids: Controlling the Formation of Cationic Clusters by the Interaction Strength of the Counterions
Author(s) -
Strate Anne,
Niemann Thomas,
Michalik Dirk,
Ludwig Ralf
Publication year - 2017
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201609799
Subject(s) - cationic polymerization , counterion , chemical physics , hydrogen bond , chemistry , ion , ionic bonding , electrostatics , dispersion (optics) , coulomb , computational chemistry , molecule , organic chemistry , physics , optics , quantum mechanics , electron
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.