2-吡嗪羧酸银的合成、晶体结构及热化学性质

Synthesis, crystal structure and thermochemistry of 2-pyrazine carboxylate silver

以二次蒸馏水为溶剂，合成了2-吡嗪羧酸银（Ag（pyza）（s）），并利用X-射线单晶衍射法表征了其晶体结构. 根据晶体结构数据计算得到2-吡嗪羧酸银的晶格能为554.10 kJ/mol. 利用TG/DSC热分析技术研究了该化合物的热分解过程；用精密自动绝热热量计测量了其在78~378 K温区的低温热容；通过最小二乘法拟合得到了摩尔热容随折合温度变化的多项式方程，利用此方程计算出该化合物的舒平热容和各种热力学函数. 通过设计合理的热化学循环，利用等温环境溶解-反应热量计分别测定了所设计热化学反应的反应物和产物在选定溶剂中的溶解焓，通过计算得到反应的反应焓为： -（31.919 ± 0.526）kJ/mol. 利用Hess定律计算出2-吡嗪羧酸银的标准摩尔生成焓为： -（243.659 ± 1.298）kJ/mol. 利用紫外-可见光谱仪对反应物和产物溶解所得溶液分别进行测量，从而证实了所设计热化学循环的可靠性.

2-Pyrazine carboxylate silver （Ag（pyza）） was synthesized in redistilled water. X-ray crystallography was applied to characterize its crystal structure. Lattice potential energy of the compound was determined from data of the crystal structure. TG/DSC simultaneous thermal analyzer was used to investigate thermal decomposition of the compound. Low temperature heat capacities in the temperature range from 78 to 378 K were measured by a fully automated adiabatic calorimeter with a small sample and a high precision. A polynomial equation of experimental molar heat capacities as a function of the temperature has been obtained. The smoothed molar heat capacities and thermodynamic functions of the compound were calculated based on the fitted polynomial equation. A reasonable thermochemical cycle was designed on the basis of the preparation reaction of the substance, and the standard molar enthalpies of dissolution for the reactants and products of the reaction in the selected solvent were measured by an isoperibol solution-reaction calorimeter. The enthalpy change of the reaction was determined to be -（31.919 ± 0.526） kJ/mol. Eventually, the standard molar enthalpy of formation of the title complex was derived to be -（243.659 ± 1.298） kJ/mol by a Hess thermochemical cycle. In addition, the reliability of the designed thermochemical cycle was verified by UV-Vis spectroscopy and refractive indexes.