Issue 42, 2010

Correlation between polarity parameters and dielectric properties of [Na][TOTO]—a sodium ionic liquid

Abstract

The ionic liquid (IL) [Na][TOTO], with sodium as the cation and an oligoethercarboxylate as the anion, shows properties that differ significantly from conventional ionic liquids, like imidazolium salts. Its polarity, determined in the temperature range of (293–333) K from measurements of Reichardt's ENT value and the Kamlet–Taft parameters is extraordinarily low and matches the dielectric constant extrapolated from frequency dependent complex permittivity measurements. The dielectric spectra also reveal split dynamics with the dominating slow mode probably associated with the reorientation of –COO⋯Na+ ion pairs and the fast mode arising from the flexibility of the oligoethylene moieties of the anion. This assignment, supported by the derived effective dipole moments, argues against our previous hypothesis [O. Zech et al., Chem.–Eur. J., 2009, 15, 1341–1345] that salts, such as [Na][TOTO], have low melting points because of cation complexation in a pseudo crown ether-like fashion and resulting “intra-molecular” charge neutralization. The present data rule out a rigid chelate-like complex as the dominating species. Considering the present findings together with the viscosities of [TOTO] salts, a crosslinked structure of the ionic liquid with strong –COO⋯Na+ interactions and relatively weaker forces between cations and ether oxygen groups of the anions appears to be plausible.

Graphical abstract: Correlation between polarity parameters and dielectric properties of [Na][TOTO]—a sodium ionic liquid

Article information

Article type
Paper
Submitted
10 Jun 2010
Accepted
07 Sep 2010
First published
06 Oct 2010

Phys. Chem. Chem. Phys., 2010,12, 14341-14350

Correlation between polarity parameters and dielectric properties of [Na][TOTO]—a sodium ionic liquid

O. Zech, J. Hunger, J. R. Sangoro, C. Iacob, F. Kremer, W. Kunz and R. Buchner, Phys. Chem. Chem. Phys., 2010, 12, 14341 DOI: 10.1039/C0CP00840K

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