DFT study on the nature of interaction of ionic liquids with self-assembled belt[14]pyridine

Abstract

Ionic liquids (ILs) are salts (which exist in liquid state) with numerous unique characteristics having extensive applications in various fields. However, there are constraints to their widespread usage in various applications due to comparatively high viscosity resulting in their slow mass transfer rates. To cope with this problem, encapsulation of ILs has been proved to be advantageous. Herein, an absolutely new approach for encapsulation of ILs is studied. We have studied the self-assembly of nitrogen-based belt[14]pyridine units (BP) resulting into generation of self-assembled nanotubes for the purpose of encapsulation of ILs. The assembly of these belts is a thermodynamically viable process which is proved through interaction energy (Eint) value equal to −87.26 kcal/mol. After the successful assembly of belt units, three different ILs i.e., tetramethylammonium chloride (TMACl), methylpyridinium hexafluorophosphate (MPHP) and 1,3-dimethylimidazolium chloride (MIMCl) have been encapsulated separately inside the cavity with Eint ranging from −50.65 to −66.96 kcal/mol. The successful transfer of charge showing strong interactions between BP and ILs has been studied through natural bond orbital (NBO) analysis which is validated further through electron density differences (EDD) analysis. In addition, the type of interactions involved in encapsulating ILs inside BP’s cavity and strength of these interactions is studied through NCI and QTAIM analysis. Both QTAIM and NCI analyses show that van der Waals forces stabilize ionic liquids inside BP cavity. Comparison shows the best results for MPHP encapsulation inside BP i.e., the highest interaction energy, the more transfer of charge and the stronger forces of interactions. Additionally, dynamical stability of assembled belt[14]pyridine units after introduction of ionic liquids into the cavity are studied through AIMD, ab initio molecular dynamics analysis. The results show that belts in assembled form are suitable for ionic liquids’ encapsulation. We hope that the new assembled belt[14]pyridine based ENIL systems will be applicable in an expansive array of different fields.