Insight into the structure and interaction properties of 1-propylnitrile-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and chloroform mixtures

Abstract

In this work, the structure and interaction properties of the mixtures of a task specific ionic liquid (TSIL) 1-propylnitrile-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([PCNMIM][Tf2N]) and chloroform (CDCl3) were elucidated by Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations. Excess infrared spectroscopy was applied to analyse the original infrared spectra. The main conclusions are: (1) stable hydrogen-bonding complexes are found in the mixtures, and they are the primary cause of the gradual shift of v(CH) of the [PCNMIM]+ cation. The hydrogen-bonds related to the aromatic CH are strengthened, while those related to the alkyl CH are weakened by the addition of CDCl3. (2) A number of species in the binary mixtures were identified, namely, ion cluster–CDCl3, ion pair–CDCl3, ion pair and ion cluster. CDCl3 cannot break apart the strong electronic interaction between [PCNMIM]+ and [Tf2N]− but can break apart the ion cluster into ion pair throughout the investigated concentration range. (3) Several hydrogen-bonds are identified in the ion cluster–CDCl3, ion pair–CDCl3, ion pair and ion cluster complexes. They are weak strength, closed shell and electrostatic dominant interactions. In addition, the hydrogen atom at the C2 site of the [PCNMIM]+ cation is the preferred interaction site.