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Proof of Ion-Pair Structures in Ammonium-Based Protic Ionic Liquids Using Combined NMR and DFT/PCM-Based Chemical Shift Calculations

Abstract

The self-assembly of triethylammonium bis(trifluoromethylsulfonyl)imide, i.e., [(C2H5)3NH][TFSI] in chloroform and aqueous solutions has been investigated using 1H NMR spectroscopy and computational (DFT/PCM prediction) methods. We have examined a number of ion pairs formed between the [(C2H5)3NH]+ cation with different conformations of alkyl substituents as well as various dispositions of the multi-site [TFSI]– anion. Based on the agreement between the calculated (DFT) and observed 1H NMR chemical shifts, [(C2H5)3NH][TFSI] in chloroform made lipophilic complexes with effective N+-H … N or N+-H … O hydrogen bonding, whereas hydrophilic complexes with Cα-H … O and Cα-H … F hydrogen bonding are found in aqueous solutions. This study provides new insight into the self-aggregation of ammonium PILs incorporating the widely used [TFSI]– anion and demonstrates the importance of solvent effects on chemical shifts. The simulations with explicit and implicit dielectric continuum solvents are found to be the most realistic method, yielding a representative ensemble of structures.

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Publication details

The article was received on 04 Jul 2017, accepted on 09 Aug 2017 and first published on 09 Aug 2017


Article type: Paper
DOI: 10.1039/C7CP04481J
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    Proof of Ion-Pair Structures in Ammonium-Based Protic Ionic Liquids Using Combined NMR and DFT/PCM-Based Chemical Shift Calculations

    M. Łożyński, J. Pernak, Z. Gdaniec, B. Gorska and F. Béguin, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP04481J

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