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On the components of the dielectric constants of ionic liquids : ionic polarization?

journal contribution
posted on 01.01.2009, 00:00 authored by E Izgorodina, Maria ForsythMaria Forsyth, D MacFarlane
According to dielectric spectroscopy measurements, ionic liquids (ILs) have rather modest dielectric constants that reflect contributions from distortion and electronic polarization caused by the molecular polarizability as well as the orientation polarization caused by the permanent dipole moment of the ions. To understand the relative importance of these various contributions, the electronic polarizabilities of 27 routinely used ionic liquid ions of different symmetry and size were calculated using ab initio-based methods such as HF and MP2. Using the Clausius–Mossotti equation, these polarizabilities were then used to obtain the electronic polarization contribution (εop) to the dielectric constants of six ionic liquids, [C2mim][BF4], [C2mpyr][N(CN)2], [C2mim][CF3SO3], [EtNH3][NO3], [C2mim][NTf2] and [C2mim][EtSO4]. Theoretical εop values were compared to experimental refractive indices of these ionic liquids as well as to those of traditional molecular solvents such as water, tetrahydrofuran (THF), dimethylsulfoxide (DMSO) and formamide. The dipole moments of the ions were also calculated, and from these it is shown that the molecular reorientation component of the dielectric constants of the ionic liquids consisting of ions with small or negligible dipole moments is quite small. Thus it is concluded that a contribution from a form of “ionic polarization” must be present.

History

Journal

Physical chemistry chemical physics

Volume

11

Issue

14

Pagination

2452 - 2458

Publisher

Royal Society of Chemistry

Location

Cambridge, England

ISSN

1463-9076

eISSN

1463-9084

Language

eng

Publication classification

C1.1 Refereed article in a scholarly journal

Copyright notice

2009, Owner Societies