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

• Thermophysical properties new data of two magnetic ionic liquids are presented.
• New data on the magnetic properties using SQUID magnetometry are reported.
• Density, viscosity and heat capacity are very different.
• Both compounds are paramagnetic, due to the presence of Fe3+ ion.
• Strong covalence effects in the [P6 6 6 14]− cation were found.

The density, heat capacity and viscosity of two magnetic ionic liquids sharing the same Fe (III)-containing anion, specifically, [C4mim][FeCl4] and [P6 6 6 14][FeCl4], 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 [C4mim][FeCl4] and [P6 6 6 14][FeCl4] are paramagnetic, but while in the first case the magnetic moment value is 5.8 μB/Fe, therefore close to that of Fe3+, for the latter it is only 4.8 μB/Fe. The effective concentration of magnetic sites is almost three times greater for [C4mim][FeCl4] as compared to [P6 6 6 14][FeCl4]. 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.

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