Conducting and magnetic properties of 1-ethyl-3-methylimidazolium (EMI) salts containing paramagnetic irons:: Liquids [EMI]MIIICl4] (M = Fe and Fe0.5Ga0.5) and solid [EMI]2[FeIICl4]

An EMI-based room-temperature (RT) ionic liquid containing d(5) trivalent iron(III) ions [EMI][(FeCl4)-Cl-III] was fully investigated, where EMI is 1-ethyl-3-methylimidazolium. The viscosity of the salt is 14 cP at 30 degrees C, and its ionic conductivity is as high as 1.8 x 10(-2) S cm(-1) at 20 degrees 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][(GaCl4)-Cl-III] and paramagnetic [EMI][(FeCl4)-Cl-III](0.5)[(GaCl4)-Cl-III](0.5) are also RT ionic liquids and show similar conductivities (1.8-2.0 x 10-2 S cm(-1) at 20 degrees C) and viscosities (12-13 cP at 30 degrees 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)[(FeCl4)-Cl-II] melts at 86 degrees C. Its crystal structure determined by a synchrotron X-ray powder diffraction measurement is analogous to those of the reported [EMI](2)[(CoCl4)-Cl-II] and [EMI](2)[(NiCl4)-Cl-II] with expanded lattice.