Abstract: Recently,ionic liquids(ILs) have received more attention because of their unusual properties and have great potential as "green" solvents for industrial processes.In particular,the ILs based on AlCl₃ have been most widely studied.However,there are a limited number of reports of ionic liquids based on elements of group Ⅲ other than aluminum.To expand our knowledge of IL chemistry and as a continuation of our previous investigations this paper reports that an ionic liquid(IL),BMIInCl₄,was prepared by directly mixing InCl₃ and 1- methyl-3-n-butylimidazolium chloride with molar ratio 1∶1 under dry argon atmosphere.The densities and surface tension of the pure IL were determined in the temperature range from 278.15 to 343.15 K.The properties for the ionic liquid based on group Ⅲ were discussed by using Glasser's theory.The values of volume of anion AlCl^-₄ and InCl^-₄ were obtained,respectively.The mean contribution of per methylene((—CH₂—)) group to the molecular volume of ionic liquid based on AlCl₃ is 0.028 6 nm³ and is in good agreement with the contribution of 0.028 0 nm³ from n-alcohols. And the standard entropy,the surface energy and the crystal energy of the ionic liquid were calculated,respectively.The crystal energy of the ionic liquid is much lower than that of ionic solid and this is the underlying reason for forming ionic liquid at room temperature.In addition,a new theoretical model of ionic liquid,that is an interstice model,was applied to calculating the thermal expansion coefficient of BMIInCl₄.And the magnitude order of the thermal expansion coefficient,α,calculated by the theoretical model is in good agreement with the experimental value.The result shows that there is much reasonableness for the interstice model of ionic liquid.

Key words: Ionic liquid, Density, Surface tension, InCl₃, Interstice model