Anti-electrostatic hydrogen bonding between anions of ionic liquids: a density functional theory study

Area of Science:

• Ionic Liquids research
• Physical Chemistry
• Computational Chemistry

Background:

• Hydrogen bonds (HBs) are critical to ionic liquid (IL) properties.
• Previous research focused on cation-anion and cation-cation HBs in ILs.

Purpose of the Study:

• To provide DFT evidence for anion-anion (An-An) HBs in the ionic liquid [HEMIm][HEIm].
• To analyze the thermodynamic stability and characteristics of An-An HBs.
• To broaden the understanding of HB interactions in ILs.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Potential energy scans for thermodynamic stability analysis.
• Geometric, spectral, and electronic structure analyses.
• Energy decomposition analysis (EDA).
• Global minimum search for ionic clusters.

Main Results:

• DFT evidence confirms the existence of An-An HBs in [HEMIm][HEIm].
• An-An HBs exhibit thermodynamic stability comparable to water dimers.
• Cation-anion pairs are the most stable, followed by H2O dimers, cationic dimers, and then anionic dimers.
• Induction and dispersion interactions are key to forming An-An HBs against Coulomb repulsion.
• An-An HBs were observed in ionic clusters, even with hydroxyl-functionalized cations.

Conclusions:

• An-An HBs are a significant interaction in ionic liquids.
• The findings support the concept of anti-electrostatic hydrogen bonds.
• This research expands the understanding of hydrogen bonding in IL systems.