We synthesized 9 kinds of FeCl3/[C4mim][Cl] magnetic ionic liquids.
Conductivity and density were measured in the T = (293.15 to 343.15) K range.
Viscosities were measured at T = 298.15 K in the whole mole composition ratio range.
Crystal energy gets lower with increasing the mole ratio of FeCl3.
The formation of [FeCl4]− and [Fe2Cl7]− influences the physicochemical properties.