Hydrogen bonding and π-π interactions in imidazolium-chloride ionic liquid clusters

Area of Science:

• Computational Chemistry
• Supramolecular Chemistry
• Physical Chemistry

Background:

• Ionic liquids and ion-pairs (IPs) exhibit complex interactions crucial for their properties.
• Understanding non-covalent interactions like hydrogen bonding (H-bonding), anion-π(+), and π(+)-π(+) interactions is key to predicting their behavior.

Purpose of the Study:

• To systematically analyze the electronic structure of H-bonding, anion-π(+), and π(+)-π(+) interactions in [C1C1im]Cl ion-pairs and dimers.
• To elucidate the role of these interactions in the structural organization and conformational flexibility of ion-pair aggregates.

Main Methods:

• Utilized a combination of Quantum Theory of Atoms in Molecules (QTAIM), NCIPLOT, Natural Bond Orbital (NBO) analysis, and qualitative Molecular Orbital (MO) theory.
• Investigated electronic structure and interaction characteristics of isolated ion-pairs and their dimers.

Main Results:

• Ion-pair dimers form charge quadrupolar arrangements, associating as clusters or loosely bound structures.
• Structural fluidity is observed with minimal energy cost, independent of cation ring orientation, driven by fluctuating interactions.
• Novel bent H-bonds and stabilized π(+)-π(+) interactions were identified; secondary H-bonds become more significant in dimers.

Conclusions:

• Secondary hydrogen bonds play an increased role in condensed phases compared to isolated ion-pairs.
• The interplay of H-bonding, anion-π(+), and π(+)-π(+) interactions dictates the structural dynamics and fluidity of ion-pair systems.