Thermophysical and magnetic studies of two paramagnetic liquid salts: [C4mim][FeCl4] and [P6 6 6 14][FeCl4]

Abstract The density, heat capacity and viscosity of two magnetic ionic liquids sharing the same Fe (III)-containing anion, specifically, [C 4 mim][FeCl 4 ] and [P 6 6 6 14 ][FeCl 4 ], have been determined, along with their volumetric expansivity, and thermal decomposition temperatures. The magnetic properties of the two compounds have been studied using SQUID magnetometry. Both [C 4 mim][FeCl 4 ] and [P 6 6 6 14 ][FeCl 4 ] are paramagnetic, but while in the first case the magnetic moment value is 5.8 μ B /Fe, therefore close to that of Fe 3+ , for the latter it is only 4.8 μ B /Fe. The effective concentration of magnetic sites is almost three times greater for [C 4 mim][FeCl 4 ] as compared to [P 6 6 6 14 ][FeCl 4 ]. In this latter case, the experimental isothermal magnetization curves do not follow a Brillouin-type of behavior; alternatively, the results were discussed using the Spin Hamiltonian formalism in terms of both the distortion of the Iron site and covalence effects.