Crystal Structure and Thermochemical Properties of 2-Pyrazine Carboxylate Lithium Monohydrate [Li（pyza）（H2O）]n（S）（pyza=2-Pyrazine Carboxylate）  

作　　者：XU Dan DI Youying KONG Yuxia DOU Jianmin 

机构地区：[1]College of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng 252059, P. R. China

出　　处：《Chemical Research in Chinese Universities》2015年第2期253-260,共8页高等学校化学研究（英文版）

基　　金：Supported by the National Natural SCience Foundation of China（Nos.20673050, 20973089, 21273100）.

摘　　要：A 2-pyrazine carboxylate lithium monohydrate [Li（pyza）（H2O）]n was synthesized in a mixed solution of redistilled water and anhydrous ethanol. X-Ray crystallography was applied to characterizing its crystal structure. Low temperature molar heat capacities were measured in a temperature range of from 78 K to 400 K with a precision automatic adiabatic calorimeter. Two polynomial equations of experimental molar heat capacity as a function of temperature were obtained by the least-squares method. The smoothed molar heat capacities and thermodynamic functions of the compound were calculated based on the fitted polynomial equations. In accordance with Hess＇s law, a reasonable thermochemical cycle was designed based on the preparation reaction of the target compound. The standard molar enthalpies of dissolution for the reactants and products of the designed thermochemical reaction were measured by an isoperibol solution-reaction calorimeter, and the enthalpy change of the reaction was obtained, i.e., △rHm^ Ф→=-（30.084±0.329） kJ/mol. The standard molar enthalpy of the formation of the target compound was determined as △fHm^ Ф→,{[Li（pyza）（H2O）n（S）} =-（260.844±1.178） kJ/mol based on the enthalpy change of the reaction and standard molar enthalpies of the formation of other reactants and products. In addition, UV-Vis spectroscopy and the data of the refractive indexes were used to confirm whether the designed Hess thermochemieal cycle was reasonable and reliable.A 2-pyrazine carboxylate lithium monohydrate [Li（pyza）（H2O）]n was synthesized in a mixed solution of redistilled water and anhydrous ethanol. X-Ray crystallography was applied to characterizing its crystal structure. Low temperature molar heat capacities were measured in a temperature range of from 78 K to 400 K with a precision automatic adiabatic calorimeter. Two polynomial equations of experimental molar heat capacity as a function of temperature were obtained by the least-squares method. The smoothed molar heat capacities and thermodynamic functions of the compound were calculated based on the fitted polynomial equations. In accordance with Hess＇s law, a reasonable thermochemical cycle was designed based on the preparation reaction of the target compound. The standard molar enthalpies of dissolution for the reactants and products of the designed thermochemical reaction were measured by an isoperibol solution-reaction calorimeter, and the enthalpy change of the reaction was obtained, i.e., △rHm^ Ф→=-（30.084±0.329） kJ/mol. The standard molar enthalpy of the formation of the target compound was determined as △fHm^ Ф→,{[Li（pyza）（H2O）n（S）} =-（260.844±1.178） kJ/mol based on the enthalpy change of the reaction and standard molar enthalpies of the formation of other reactants and products. In addition, UV-Vis spectroscopy and the data of the refractive indexes were used to confirm whether the designed Hess thermochemieal cycle was reasonable and reliable.

关 键 词：2-Pyrazine carboxylate lithium monohydrate Crystal structure Low temperature heat capacity Enthalpy of the dissolution Standard molar enthalpy of formation 

分 类 号：O614.121[理学—无机化学] TE642[理学—化学]