Theoretical Study of Cation-Anion Interactions in Ammonium-Based Ionic Liquids: The Effect of Functionalization and Alkyl Chain Length

Ionic liquids are a class of novel compounds composed of organic cations and inorganicanions. So with selection of cation and anion or by introducing a functional group to thestructure, we able to design different ionic liquids for various applications [1].The study of cation-anion interaction is important in theoretical point of view. In this work,interaction energies in ion pairs of ammonium-based ionic liquids and their ether functionalizedhave been studied. The investigated cations are triethyl(methyl)ammonium, [N2221]+,tributyl(methyl)ammonium, [N4441]+, and their ether functionalized cations, [N2221-O]+ and[N4441-O]+, which paired with chloride as anion. Potential energy curves for cation-anioninteractions have been computed with DFT and an atom pair-wise corrected dispersion DFTmethod (DFT-D3) [2] and compared with Møller–Plesset second-order (MP2) as a reference.Dispersion interactions were important in the overall stabilization of ionic liquids contributingfrom 2.46 kcal.mol-1 for [N2221-O]Cl to 4.27 kcal.mol-1 for [N4441]Cl (about 2.7 to 4.7 % ofthe interaction energy). The contribution of dispersion energy was found to increase inmagnitude with increasing alkyl side chain length and to decrease with ether functionalization.There is no clear trend in cation-anion interaction energies with the alkyl chain lengthening and etherfunctionalization of the studied ionic liquids.

کلیدواژه ها:

Computational Chemistry ، DFT ، DFT-D3 ، Interaction Energy ، Dispersion Interaction ، Ionic Liquids