Conformation features and interaction of pyrrolidinium-based ionic liquids immobilized with silicon dioxide: Infrared spectroscopy

Abstract

Ionic liquids (ILs) based on pyrrolidinium cation, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPyrrTFSI) and 1-butyl-1-methylpirrolidinium dicyanamide (BMPyrrN(CN)2), were incorporated into the silica matrix (SiO2, particle size about 80 nm) by a simple mixing procedure. Semitransparent phase-stable ionogels with an IL content of more than 90 wt% have been obtained and studied by FTIR spectroscopy. The analysis of microscopic mechanisms of interaction, in particular, hydrogen bonding, was carried out using the procedure of fitting the characteristic bands of pure and confined ILs. The observed changes in the position and intensity of some characteristic frequencies were interpreted in terms of the interaction of SiO2 with IL. Under confined condition, the cis–trans equilibrium of both the TFSI− anion and BMPyrr+ cation changes in favor of the trans population due to the predominant interaction of cis conformers with silica walls. This data for confined BMPyrr-based ionic liquids were obtained in our study for the first time and will be useful for designing of a new nanostructured hybrid materials with promising properties.