Superhalogens as Building Blocks of Ionic Liquids

Area of Science:

• Materials Chemistry
• Computational Chemistry
• Physical Chemistry

Background:

• Ionic liquids (ILs) typically use complex anions for stability.
• Some complex anions, like BF4 and PF6, are classified as superhalogens.
• The potential of superhalogens in designing novel ILs remains underexplored.

Purpose of the Study:

• To investigate the feasibility of using superhalogens as building blocks for new ionic liquids.
• To explore the stability and electronic properties of ionic liquid complexes involving superhalogen anions.

Main Methods:

• Density Functional Theory (DFT) calculations using the ωB97XD/6-311++G(d,p) level of theory.
• Quantum Theory of Atoms in Molecule (QTAIM) analysis.
• Study of 1-butyl-3-methylimidazolium (BMIM) cation complexes with various superhalogen anions (e.g., LiF2, BeF3, BO2, NO3, BF4, PF6, Cl).

Main Results:

• BMIM-superhalogen complexes exhibit significant charge transfer (0.90-0.97 e) from BMIM to the superhalogen anion.
• Complex stability is enhanced by ionic, covalent, and hydrogen bonding interactions.
• Complexes preferentially dissociate into ionic fragments (BMIM+ + X-) rather than neutral fragments.
• Dissociation energy and energy gap correlate with the superhalogen's electron affinity.

Conclusions:

• Superhalogens are viable components for constructing stable ionic liquids.
• The electron affinity of superhalogens directly influences the stability of the resulting ionic liquids.
• This study provides a pathway for designing highly stable ionic liquids by selecting appropriate superhalogen anions.