Document Type : Original Article

Authors

• Saeid Yeganegi ¹
• Azim Soltanabadi ²

¹ Physical Chemistry, Faculty of Chemistry, University of Mazandaran, Babolsar, Iran

² Faculty of Chemistry, Razi University, Kermanshah, 6714414971, Iran

Abstract

In this study, the properties of the geminal dicationic ionic liquids (DILs) 1,3- bis[3-methylimidazolium-1-yl] butane halides ([C4(mim)2][X]2, X¯ = Cl¯, Br¯ and I¯) were studied using the molecular dynamic simulation (MD) and density functional theory (DFT). The liquid structure of [C4(mim)2][X]2 (X=Cl, Br, I) was analyzed by radial distribution function(RDF), dihedral angle distribution of n-butyl side chains in the [C4(mim)2]+2 cations, distance between two rings in the [C4(mim)2]+2, spatial distribution function (SDF) and combined distribution function (CDF). The calculated RDFs show that anions spend most of their time around the hydrogens attached to the cation rings. The calculated SDFs show that the halide anions show the highest probability densities around the hydrogen atoms of the imidazolium rings. The calculated diffusion coefficients show that the diffusivities of the anions are one order of magnitude higher than that of cations and other hydrogen atoms. The effects of anion type on the diffusion coefficient were also studied. DFT calculations show that the most stable structure of the cation in the DIL is a U-shaped form, where the rings of cation bend towards each other and anions are close to the atoms of both rings. Our results show that hydrogen bonding is crucial in the interaction between the [C4(mim)2]+2 cation and anion atoms in the most stable configurations of an ion pair. These hydrogen bonds were analyzed by the atoms in molecules (AIM) and natural bond orbital (NBO) analysis. The ion pair interactions decrease with increasing the halide atomic weight.

Keywords

• Geminal IL
• molecular dynamic simulation
• RDF
• diffusion
• interaction
• electronic structure
• AIM