Mechanical spectroscopy study of ionic liquids with quaternary cations: Effect of conformational flexibility

Mechanical spectroscopy measurements were performed on ionic liquids (ILs) with quaternary cations, either ammonium or phosphonium, and two anions, bis(trifluoromethanesulfonyl)imide ([NTf2]-) and bis(trifluoromethanesulfonyl)methanide ([CHTf2]-), which have almost the same molecular weight and degr...

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Bibliographic Details
Published in:Journal of alloys and compounds 2022-10, Vol.919, p.165860, Article 165860
Main Authors: Palumbo, O., Paolone, A., Rauber, D., Kay, C.W.M., Philippi, F., Welton, T.
Format: Article
Language:English
Subjects:
Anions
Cations
Configurations
Conformers
Flexibility
Fluorination
Ionic liquids
Ions
Liquid phases
Mechanical spectroscopy
Phase transitions
Relaxation
Spectrum analysis
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Summary:Mechanical spectroscopy measurements were performed on ionic liquids (ILs) with quaternary cations, either ammonium or phosphonium, and two anions, bis(trifluoromethanesulfonyl)imide ([NTf2]-) and bis(trifluoromethanesulfonyl)methanide ([CHTf2]-), which have almost the same molecular weight and degree of fluorination but exhibit different flexibility. Furthermore, the effect of multiple ether functionalization was studied by measuring the mechanical spectrum of [P(2O2)31][CHTf2]. The measured data evidence the occurrence of a relaxation process in the liquid phase of the ILs with flexible [NTf2]- anion and of [P(2O2)31][CHTf2], which is analyzed by means of a modified Debye model relating the peak to the ion hopping between non-equivalent configurations. The analysis confirms the involvement of nonequivalent anion configurations as well as their energy separation. For other ILs having rigid ions, instead, a fast dynamic at local level in the liquid phase is rarely observed since a partial transition to a solid state is favored. For these liquids, the measurements suggest the formation of aggregates which is suppressed by the multiple ether functionalization. •Mechanical spectroscopy on ILs with ammonium or phosphonium quaternary cations.•Occurrence of a relaxation process in the ILs with flexible ions.•Involvement of nonequivalent anion configurations as well as their energy separation.•For other ILs having rigid ions a partial transition to a solid state is favored.
ISSN:0925-8388
1873-4669
DOI:10.1016/j.jallcom.2022.165860