Abstract

X-ray photoelectron spectroscopy is used to investigate the impact of methylation on the electronic environment of pyridinium cations. Because of the electron-donating effect of the methyl group, there is a significant increase in electron density on the cationic nitrogen. The shift of the N 1s binding energy is inversely proportional to the anion basicity. The methylation position on the electronic environment of the cationic nitrogen is investigated. The N 1s binding energy follows the trend: 1-octylpyridinium > 1-octyl-3-picolinium > 1-octyl-4-picolinium > 1-octyl-2-picolinium, which is in good agreement with the cation acidity. The increase in the inductive effect subsequently weakens the cation-anion interactions through charge transfer from the anion to the cation, causing a subtle change in the electronic environment of the anion. Such an effect is noticeably reflected in the Br 3d binding energy. It shows that the Br 3d5/2 binding energy of 1-octyl-2-picolinium bromide is 0.2 eV lower than that of 1-octylpyridinium bromide.

Highlights

  • Ionic liquids (ILs) are considered as tuneable solvents, since there are nearly an endless number of combinations of cations and anions, each of which is of distinct physicochemical properties.[1]

  • X-ray photoelectron spectroscopy is used to investigate the impact of methylation on the electronic environment of the pyridinium cation

  • Due to the electron donating effect of the methyl group, there is a significant increase in electron density on the cationic nitrogen

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Summary

Introduction

Ionic liquids (ILs) are considered as tuneable solvents, since there are nearly an endless number of combinations of cations and anions, each of which is of distinct physicochemical properties.[1] By selecting the cation, the anion and the mixture composition, it is feasible to design ILs with desired properties, such as melting point, viscosity, solubility, hydrophobicity, thermal stability, etc. This tunability has become the most unique advantages of ILs, making them potential materials in a wide range of applications, such as chemical reactions,[2,3] lubrication,[4] phase separation,[5,6] CO2 capture,[7] desulfurization of fuel[8] and electrochemistry.[9,10].

Experimental section
Results and discussion
Conclusions

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