Synthesis, vibrational and thermal studies of new 3,3′-dibutyl-1,1′-(1,4-phenylenedimethylene)-bis (1H-imidazolium) ionic liquids: an experimental and quantum computational investigation

In recent years, scientific studies have proven that dicationic ionic liquids (DILs) are moresuitable for some applications than monocationic ionic liquids (ILs), which created a qualitative leap to more interest in delving into the study of the variousproperties of this type of compounds and prompted scientists to do more syntheses in this research field.Our dicationic ionic liquids (DILs) composed of 3,3′-dibutyl-1,1′-(1,4-phenylenedimethylene) - bis (1H-imidazolium) [p-C6H4(CH2ImBu)2]+2 cation paired with halogenated [Br]−, inorganic hexafluorinated [PF6]−, and organic fluorinated [NTf2]− anions are prepared by microwave synthesis for the first DIL and metathesis for the others, to investigate the effects of electron delocalization on their structures and the mutual interactions between cation and anions on their physical and thermal properties. The thermal stability of our DILs was investigated by TGA and DTA measurements. Thermogravimetric analysis revealed that these DILs were found to be highly thermally stable with decomposition temperatures occurring well above 340°C, and up to 500°C for the bis (trifluoromethylsulfonyl) Imide DIL. In the other hands, the vibrational spectra of our dicationic ionic liquids (DILs) have been recorded in the regions 3500−600 cm−1 and 4000−45 cm−1by Fourier transform infrared (FTIR) and Raman spectroscopy, respectively. Density functional theory calculations (DFT) have been used at M06-2X/Aug-CC-pVDZ level of theory to investigate structural and electronic properties as well as to predict some physicochemical properties of the DILs.