Low-temperature heat capacities and standard molar enthalpy of formation of 2-pyrazinecarboxylate cupric(II) complex Cu(pyza)2(H2O)2

Abstract

2-Pyrazinecarboxylate cupric(II) complex Cu(pyza)2(H2O)2(s) was synthesized by the method of liquid phase synthesis. The composition and structure of the compound were characterized by chemical and elemental analyses and X-ray crystallography. Low-temperature heat capacities of the compound were measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 400 K. A polynomial equation of the heat capacities as a function of the temperature was fitted by the least-square method. The smoothed heat capacities and the thermodynamic functions of the compound relative to 298.15 K were calculated and tabulated at an interval of 5 K. In accordance with Hess’ law, a thermochemical cycle was designed, the enthalpy change in the reaction of 2-pyrazinecarboxylic acid with cupric acetate monohydrate was determined by the use of an isoperibol solution-reaction calorimeter, and the standard molar enthalpy of formation of the complex was calculated to be −(1191.282 ± 2.457) kJ mol−1 by the use of the dissolution enthalpies and other auxiliary thermodynamic quantities.