Synthesis And Thermodynamics Properties Of Rare Metal(Mo,Sb,Co) Ionic Liquids

Rare metal compounds have unique structures and properties.Different rare metal ionic liquids can be obtained by structural design,which have a wide application prospect.In this paper,1-butyl-3-alkyl imidazolium molybdate[C_nbim]₂[MoO₄](n=1,2,3),1-alkyl-3-alkyl imidazolium hexafluoroantimonate[C_nC_nim][SbF₆](n=3/4),1-(2-Methoxyethyl)-3-alkyl imidazolium tetraisothiocyanato-cobaltate(II)[C_n2O1IM]₂[Co(NCS)₄](n=1,2,3),N-alkyl pyridine tetraisothiocyanato-cobaltate(II)[C_nPy]₂[Co(NCS)₄](n=5,6)were synthesized and characterized by ¹H-NMR,¹³C-NMR,IR,Raman and ESI-MS,and the target products were identified.The density,surface tension,refractive index and conductivity of various rare metal ionic liquids were measured in the range of 293.15 K?343.15 K.The thermal expansion coefficient?of rare metal ionic liquids was calculated.The pore volume,porosity of ionic and the molecular volume of ionic liquids were obtained.The relationship between the molecular volume of ionic liquids and the length of cationic alkyl chain was discussed.Based on the Glasser theory,the standard entropy S₀(298 K),lattice energy U_pot and surface energy E_a of ionic liquids were calculated respectively.The structure-activity relationship between the structure and properties of ionic liquids was analyzed through the above calculation data,and the reason for the melting state of ionic liquids at room temperature was explained from the perspective of lattice energy.By introducing the Gibbs free energy of the molar surface,the traditional E(?)tv(?)s equation is improved and a new E(?)tv(?)s equation is obtained.The slope and intercept have clear physical meaning:the slope represents the enthalpy of the molar surface,and the intercept represents the entropy of the molar surface.Combined with the refractive index of rare metal ionic liquids and the obtained molar surface Gibbs free energy,the surface tension was estimated,and the fitting rate between the results and the corresponding experimental values was more than 0.99.At the same time,the concept of Gibbs free energy of interval molar surface is introduced by expanding the interval theoretical model,and it is found that the value,interval molar surface entropy and interval molar surface enthalpy are constants independent of the type of ionic liquid,only related to the volume and shape of the interval.Finally,the relationship between ionic liquid conductivity and temperature was studied,the activation energy,molar conductivity and diffusion coefficient of ionic liquid conductivity were obtained,and the relationship was summarized.The evaporation enthalpies of various rare metal ionic liquids at average temperature,(?)₁^gH_m^?(T_av),were determined by constant temperature thermogravimetry.On the basis of statistical thermodynamics and Verevkin's method,the thermal tolerances of ionic liquids in gas and liquid phases are estimated respectively.The(?)₁^gH_m^?(Tav)is converted to the evaporation enthalpy at 298.15 K,and the enthalpy of evaporation at various temperatures is calculated.The calculated results are compared with the(?)₁^gH_m^?(298.15 K)estimated by Kabo and Rebolo empirical equations.The comparison of(?)₁^gH_m^?(298.15 K)verifies the rationality of the constant temperature thermogravimetric test of the evaporation enthalpy,and polarity was estimated through calculating the solubility parameters.The low temperature heat capacity of rare metal ionic liquids in the temperature range of 78 K?400 K was measured by low temperature adiabatic calorimeter.The polynomial fitting equation of ionic liquid was obtained by the least square method.The relative deviation between the fitting value and the experimental value was less than 0.6%.Finally,in order to facilitate the follow-up study,H_T–H_298.15,S_T–S_298.15 and G_T–G_298.15 of ionic liquids in the temperature range of 298.15 K?400 K were calculated,and the effects of cationic alkyl chain length on thermochemical properties and related thermochemical parameters were discussed.Through the above research on the thermodynamic properties of rare metal ionic liquids,the comparison between the experimental values and the estimated values verifies the rationality of the semi empirical estimation,and established a bridge between the structure and properties of ionic liquids.This paper is not only of great significance for the follow-up study of thermodynamic properties and the screening of target ionic liquids,but also plays a role in promoting the industrialization and development of ionic liquids.