Introduction and investigating some properties of new dicationic ionic liquid with a chelate-based spacer of Fe-Schiff Base complex (ChILs): a computational chemistry approach

Abstract

Metal-containing ionic liquids (M-ILs) show clear advantages over conventional ILs, especially in applications such as magnetic, medicine and drug delivery engineering. The design and identification of suitable ILs with desirable physicochemical properties is a major challenge for researchers in various fields of science. In this work, using density functional theory (DFT) calculations, we have investigated a series of ion triplets (ITs) based on imidazolium dicationic with a spacer based on transition metals chelated by Schiff bases (ChILs) by varying the type of anion. To determine the importance of non-covalent interactions such as dispersion and hydrogen bonding, calculations were performed with three different functionals (M06-2X-GD3, B3LYP-GD3 and M06-2X). To explore the effect of the type of anions, the five ChILs structures, [FeL(mim)₂][X]₂, (mim: methylimidazolium and X: [NO₃]⁻, [BF₄]⁻, [CF₃SO₃]⁻, [PF₆]⁻ and [AlCl₄]⁻), were optimized. Theoretical investigations were carried out on the structural, electronic and magnetic properties of the ChILs. The interaction energies of the ChILs range from -206.17 to -176.48 kcal mol⁻¹, follow the order [FeL(mim)₂][AlCl₄]₂ < [FeL(mim)₂][PF₆]₂ < [FeL (mim)₂][CF₃SO₃]₂ < [FeL(mim)₂][BF₄]₂ < [FeL(mim)₂][NO₃]₂. NBO and AIM analyses confirm that the anions, in addition to electrostatic interactions, have strong hydrogen bonding with the C − H2(C − H2′) and (C − H3(C − H3′) bonds of the dication. Also, some of their physical and chemical properties such as stability in different solvents, dipole moment and magnetic moment were calculated. This study can be useful in understanding the structure–property relationships of ChILs and contribute to the design and synthesis of new ChILs.