DFT study of 1,4-diazabicyclo[2.2.2]octane (DABCO) based ionic liquids: Effect of alkyl chain and anion types

Abstract

This study examines how 1,4-diazabicyclo[2.2.2]octane (DABCO) interacts with different anions and alkyl chain lengths ([C_nDABCO⁺][X¯], where n = 0, 1, 2, or 3, and X = Cl¯, Br¯, PF₆¯, or BF₄¯). We used Density Functional Theory (DFT) with the 6–311++G(d,p) basis set for geometry optimization and electronic property calculations. Atoms in Molecules (AIM) and Natural Bond Orbital (NBO) analyses were applied to understand bonding and charge distribution. By incorporating AIM and NBO analyses, we gained insight into the nature of bonding and charge distribution within the complexes. Larger anions like PF₆¯, or BF₄¯exhibit higher electronic stability than smaller halide anions. A key finding of this work is the substantial role of hydrogen bonding, as revealed by AIM analysis, particularly in systems involving PF₆¯, or BF₄¯. These hydrogen bonds are shown to enhance the structural stability of the ILs and contribute to their distinctive physicochemical behaviors.