Abstract
This work aims at unravelling the interactions in magnetic ionic liquids (MILs) by applying Symmetry-Adapted Perturbation Theory (SAPT) calculations, as well as based on those to set-up a polarisable force field model for these liquids. The targeted MILs comprise two different cations, namely: 1-butyl-3-methylimidazolium ([Bmim]+) and 1-ethyl-3-methylimidazolium ([Emim]+), along with several metal halides anions such as [FeCl4]−, [FeBr4]−, [ZnCl3]− and [SnCl4]2− To begin with, DFT geometry optimisations of such MILs were performed, which in turn revealed that the metallic anions prefer to stay close to the region of the carbon atom between the nitrogen atoms in the imidazolium fragment. Then, a SAPT study was carried out to find the optimal separation of the monomers and the different contributions for their interaction energy. It was found that the main contribution to the interaction energy is the electrostatic interaction component, followed by the dispersion one in most of the cases. The SAPT results were compared with those obtained by employing the local energy decomposition scheme based on the DLPNO-CCSD(T) method, the latter showing slightly lower values for the interaction energy as well as an increase of the distance between the minima centres of mass. Finally, the calculated SAPT interaction energies were found to correlate well with the melting points experimentally measured for these MILs.
Highlights
Ionic liquids (ILs) are a class of salts, usually composed of a large organic cation and a small organic or inorganic anion, that have melting points below 100 ◦ C [1]
66 of of 17 alkyl chain, meaning that [ZnCl3] slightly vertically departs from the cation’s plane. This alkyl chain, meaning that [ZnCl3 ] slightly vertically departs from the cation’s plane. This different behaviour could be due to the planar structure of the anion, with an indifferent behaviour could be due to the planar structure of the anion, with an increased creased interaction surface with the cation, while the tetrahedral geometry of the previous interaction surface with the cation, while the tetrahedral geometry of the previous anions anions shows a preference for a higher departure but closer to the 5-membered ring
Following lowing the same trend as the previous magnetic ionic liquids (MILs), the last system, the [Bmim]2[SnCl4] trimer the same trend as the previous MILs, the last system, the [Bmim]2 [SnCl4 ] trimer adopts a adopts a triangular shape in which the Sn atom is found near the C2 atom of the imidaztriangular shape in which the Sn atom is found near the C2 atom of the imidazolium ring
Summary
Ionic liquids (ILs) are a class of salts, usually composed of a large organic cation and a small organic or inorganic anion, that have melting points below 100 ◦ C [1]. In 2004, a new subclass of ILs has been discovered [6], so-called magnetic ionic liquids (MILs), which involve the incorporation of transition metal (iron, cobalt, cadmium) or rare earth elements (gadolinium, dysprosium) in the anion or cation structure [7]. The properties of these new MILs are similar to common previous ILs but with the advantage that they strongly respond to external magnetic fields. The magnetic response allows the possibility of magnetic separation, this being one of the keys that turns them into a better option than other ILs for green chemistry practices, and viscosity manipulation become worthy to be implemented in different industrial processes [12,13]
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