An EMI-based room-temperature (RT) ionic liquid containing d5 trivalent iron(III) ions [EMI][FeIIICl4] was fully investigated, where EMI is 1-ethyl-3-methylimidazolium. The viscosity of the salt is 14 cP at 30°C, and its ionic conductivity is as high as 1.8 × 10-2 S cm-1 at 20°C. The high conductivity and fluidity can be attributed to the reduced interionic Coulomb attractions owing to the nephelauxetic effect. Magnetic susceptibility shows the Curie-Weiss behavior arising from S = 5/2 high-spin electronic state on iron(III) ions in both liquid and solid states, leading to the conductive-paramagnetic bifunctional RT ionic liquid. The solidified salt passes through an antiferromagnetic transition at 4.2 K. Diamagnetic [EMI][GaIIICl 4] and paramagnetic [EMI][FeIIICl4] 0.5[GaIIICl4]0.5 are also RT ionic liquids and show similar conductivities (1.8-2.0 × 10-2 S cm-1 at 20°C) and viscosities (12-13 cP at 30°C). These results indicate that the influence of paramagnetic iron(III) ions upon the ionic conductivity and viscosity is negligible in the present system. A 2:1 EMI salt containing d 6 divalent iron(II) ions [EMI]2[FeIICl 4] melts at 86°C. Its crystal structure determined by a synchrotron X-ray powder diffraction measurement is analogous to those of the reported [EMI]2[CoIICl4] and [EMI] 2[NiIICl4] with expanded lattice.
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