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Issue 12, 2018
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The effect of ether-functionalisation in ionic liquids analysed by DFT calculation, infrared spectra, and Kamlet–Taft parameters

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Abstract

The effect of ether-functionalisation on ionic liquids (ILs) is discussed based on Kamlet–Taft parameters and the infrared (IR) spectra of N-ethoxyethyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide ([P1,2O2][TFSI]) and N-ethoxyethyl-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide ([M1,2O2][TFSI]). The results are analysed taking into consideration their ion conformers, electronegativity and hardness, and the IR active vibrations obtained by means of DFT calculations. From the evaluation of Kamlet–Taft parameters, the ether-functionalisation in the cationic ring is found to improve the polarity and hydrogen bond acidity of the ILs. This correlates with the computational result which designates that the oxygen atom in the cationic ring increases the electronegativity of the cation. The comparison with the IR spectra, which were obtained experimentally and computationally, revealed that trans-[TFSI] was preferably formed in [M1,2O2][TFSI] compared to [P1,2O2][TFSI]. Although the Kamlet–Taft parameters indicate that [M1,2O2][TFSI] has a higher polarity, this IL preferably adopts trans-[TFSI], which is normally stabilised with the cations having a lower polarity. This may be due to the presence of the oxygen in the cationic ring which delocalises the electron density of the lowest unoccupied molecular orbitals (LUMO) and increases the conformational freedom of the hydrogen bonds between cations and anions. Moreover, the mixtures of pure ILs with a suitable Li-salt were also investigated to analyze the effect of the Li salt on the polarity and the ion conformers.

Graphical abstract: The effect of ether-functionalisation in ionic liquids analysed by DFT calculation, infrared spectra, and Kamlet–Taft parameters

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Publication details

The article was received on 04 Dec 2017, accepted on 16 Feb 2018 and first published on 23 Feb 2018


Article type: Paper
DOI: 10.1039/C7CP08134K
Citation: Phys. Chem. Chem. Phys., 2018,20, 7989-7997
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    The effect of ether-functionalisation in ionic liquids analysed by DFT calculation, infrared spectra, and Kamlet–Taft parameters

    A. Tsurumaki, F. Trequattrini, O. Palumbo, S. Panero, A. Paolone and M. A. Navarra, Phys. Chem. Chem. Phys., 2018, 20, 7989
    DOI: 10.1039/C7CP08134K

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