BACKGROUNDThe behaviour of a new generation of Ionic Liquids (ILs) containing transition metals, Magnetic Ionic Liquids (MILs), has recently been reported in the literature. Due to the early stage of development of MILs, it is necessary to evaluate their properties in order to develop new applications. In this work, four MILs based on the trihexyl(tetradecyl)phosphonium cation and different magnetic anions ([P-66614](2)[CoCl4], [P-66614][FeCl4], [P-66614](2)[MnCl4] and [P-66614](3)[GdCl6]) were synthesized and characterized by measuring magnetic susceptibility, density, viscosity, thermal properties and carbon dioxide solubility for CO2 separation. RESULTSThe magnetic susceptibility showed a paramagnetic behaviour in all the MILs tested, in good agreement with other MILs reported in the literature. The density and viscosity of MILs were obtained experimentally and correlated using Fitteia software. All MILs studied showed very good thermal stability, with decomposition temperatures higher than 619K. CO2 solubility in the MILs was lower than in other ILs reported in the literature for CO2 capture under the same operational conditions. CONCLUSIONSThis work provides further information related to the synthesis and characterization of phosphonium-based MILs and offers potential for the development of new applications. (c) 2014 Society of Chemical Industry.