Geometry and Electronic Structure of Mono‐, Di‐, and Tri‐Cationic Ionic Liquids

ABSTRACT

Structures of mono cationic di cationic and tri cationic ionic liquids [M] ⁺ , [D] ⁺⁺ , and [T] ⁺⁺⁺ with halide anions (X) where X = Cl¯, Br¯, and I¯ were studied using density functional theory (DFT). The most stable geometry of this structures were computed and compared with others. In di‐cationic ionic liquids, the anions were placed in the middle of two imidazolium rings and created a U‐like structure. So that the anion was close to the imidazolium ring. In tricationic ionic liquids, the anions are placed in the middle of the three imidazolium rings and the substituents attached to the benzene are bent toward each other, creating a tripod‐like structure so that the anion is close to the imidazolium ring. The examination of intermolecular hydrogen bonding was conducted through natural bond orbital (NBO) analysis. The derived thermodynamic data indicates that the cation–anion interactions are notably stronger in ionic liquids with bromide anions compared to others. Furthermore, tri‐cationic ionic liquids exhibit a higher degree of interaction than their di‐cationic and mono‐cationic counterparts. Stability and activity by molecular orbital theory calculated and discussed. Also, mono and tri cationic ionic liquids containing iodine anion have a high dipole moment compared to di cationic ionic liquids.