Tunable ionic liquids based on substituted 2,6-dimethyl-pyridinium cation: prediction of some of their physical and chemical properties using density functional theory

Document Type : Research Article

Authors

1 Department of Chemistry, Faculty, University of Guilan , Rasht, Iran

2 university of guilan

3 Department of Chemistry, University of Payam Noor Ardabil, Ardabil

Abstract

Properties of the ionic liquids can be controlled by using different combinations of the cations and anions for specific purposes. In this work, density functional theory has been used at M062X/6311++G(2d,2p) level of theory to investigate the effect of different substitutions on the electrochemical, physical and chemical properties of the pyridinium-based ionic liquids including 4X-Dimethylpyridinium cations ([4X-DMPy]+, X: NH2, OMe, Me, H, Cl, CHO, CF3, CN and NO2) and tetrafluoroborate anion ([BF4]-). Cathodic potential limit and anodic potential limit, electrochemical window, charge transfer values, structural parameters and topological properties of the ionic liquids were calculated. The results show that the strength of the interaction between the cations and anion increases with the increase in the electron withdrawing strength of the substituents on the 4 position of the pyridinium cation ring. According to the calculated interaction energies (from -104.71 to -90.59 kcal mol-1), the stability of the studied ionic liquids is as follows: [NO2-DMPy][BF4] > [CN-DMPy][BF4] > [CF3-DMPy][BF4] > [CHO- DMPy][BF4] > [Cl-DMPy][BF4] > [H-DMPy][BF4] > [Me-DMPy][BF4] > [OMe-DMPy][BF4] > [NH2-DMPy][BF4]. Comparing the charge of the atoms from natural bond orbital analysis show that hydrogen bonding in the designed ionic liquids is accompanied by some charge transfer from anion to the cations, and the charge transfer for electron-withdrawing substituents (CHO) is greater than other substituents in [4X-DMPy][BF4] ionic liquids. According to he values electrochemical window of the studied ionic liquids (from 2.73 to 4.32 V), it is predicted that the ionic liquids containing electron-donating substituents are more suitable electrolytes than other ionic liquids in electrochemical reactions.

Keywords

Main Subjects