Electrical conductivity in two mixed-valence liquids?

Physical Chemistry Chemical Physics Pub Date: 2015-05-05 DOI: 10.1039/C5CP01172H

Abstract

Two different room-temperature liquid systems were investigated, both of which conduct a DC electrical current without decomposition or net chemical transformation. DC electrical conductivity is possible in both cases because of the presence of two different oxidation states of a redox-active species. One system is a 1?:?1 molar mixture of n-butylferrocene (BuFc) and its cation bis(trifluoromethane)sulfonimide salt, [BuFc+][NTf2?], while the other is a 1?:?1 molar mixture of TEMPO and its cation bis(trifluoromethane)sulfonimide salt, [TEMPO+][NTf2?]. The TEMPO–[TEMPO+][NTf2?] system is notable in that it is an electrically conducting liquid in which the conductivity originates from an organic molecule in two different oxidation states, with no metals present. Single-crystal X-ray diffraction of [TEMPO+][NTf2?] revealed a complex structure with structurally different cation–anion interactions for cis- and trans [NTf2?] conformers. The electron transfer self-exchange rate constant for BuFc/BuFc+ in CD3CN was determined by 1H NMR spectroscopy to be 5.4 × 106 M?1 s?1. The rate constant allowed calculation of an estimated electrical conductivity of 7.6 × 10?5 Ω?1 cm?1 for BuFc–[BuFc+][NTf2?], twice the measured value of 3.8 × 10?5 Ω?1 cm?1. Similarly, a previously reported self-exchange rate constant for TEMPO/TEMPO+ in CH3CN led to an estimated conductivity of 1.3 × 10?4 Ω?1 cm?1 for TEMPO–[TEMPO+][NTf2?], a factor of about 3 higher than the measured value of 4.3 × 10?5 Ω?1 cm?1.

Graphical abstract: Electrical conductivity in two mixed-valence liquids
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