Estimation of the Thermophysical Properties of Pentaalkylguanidinium‐Based Magnetic Ionic Liquids with Unusual Thermal Expansion Coefficient

Abstract The thermal expansion coefficient (αexp.), the molecular volume (Vm), the entropy of surface formation (Sa), and the Gibbs energy of surface formation (Ea) of four pentaalkylguanidinium‐based MILs [CnTMG][FeCl3Br] (n=2, 4, 6, 8) were calculated based on the density and surface tension data determined from 278.15 to 323.15 K. In terms of classical semiempirical methods, the standard molar entropy (S0), the lattice energy (UPOT), the molar enthalpy of evaporation ( , (298 K)), and the thermal expansion coefficient (αest.) of the MILs were further estimated. The estimation results indicate that the classical semiempirical methods are suitable for estimating the thermophysical properties of the MILs, except the unusual αexp., which were extremely larger than those of representative non‐magnetic ionic liquids (ILs). We further optimized the estimation methods and discussed the potential reasons for the unusual thermal expansion coefficient of the MILs.