The Structure And Physical Property Of Chelate-Based Ionic Liquids

In this paper,the physical properties and single crystal structure of chelate-based metal containing ionic liquids(ChILs)were studied.ChILs possess properties of both complexes and ionic liquids(ILs)and have potential application in many fields.However,researches focused on the physical properties of ChILs are still limited at present.This paper mainly focused on the physical properties and structure of ChILs to describe their characteristics and attempted to explain the differences between properties by associating the physical properties and structure.Three ChILs of different metals[C10mim][M(hfac)3](M = Co,Ni,Cu)have been synthesized and purified by repeated extraction.Densities and viscosities were measured in the temperature range(328.15-343.15)K,conductivities and surface tensions were measured in the temperature range(323.15-343.15)K,and melting points were also determined.Compared with the experimental data,three ChILs have smaller differences in density and melting point,larger differences in viscosity and conductivity and the surface tensions are basically the same.The lattice energies of ChILs were calculated according to Glasser formula and the standard molar entropies were also estimated.The molar enthalpies of evaporation of ChILs were estimated by Kabo's method.Walden rule was used to compare the ionicity of the three ChILs and it was found that the differences among three ChILs were relatively small.Compared with the physical properties of conventional ionic liquids,ChILs have a larger molecular volume,higher viscosity,lower lattice energy,conductivity and surface tension as the existence of large anions.Single crystals of ChILs were prepared and the structures were determined by X-ray crystal diffraction.Compared with different single crystal configurations,it was found that the hydrogen-bond interaction in the lattice is quite different.Based on the quasi-lattice theory,liquid and single crystal structure were connected.Taking single crystal as the starting point,the short-range ordered stacking of the ionic liquid were discussed.In combination with the physical properties data,the differences caused by the different chain lengths and metals of the ChILs were explained by analyzing the hydrogen-bond interaction inside the unit cell.