Synthesis, Structure and Thermochemistry of Pyridine-2,6-dicarboxylic Acid Lithium Hydrogen

Pyridine-2,6-dicarboxylic acid lithium hydrogen[Li(HDPC) (H2O)] was synthesized in methanol and water mixed solvent. X-ray crystallography was applied to characterize its crystal structure. A polynomial equation of experimental molar heat capacities as a function of the temperature was 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 hydrothermal reaction in the selected solvent were measured by an isoperibol solution-reaction calorimeter, respectively. The reaction enthalpy was determined to be -(46.83 +/- 0.16) kJ/mol. Eventually, the standard molar enthalpy of formation of the title complex was derived to be -(747.90 +/- 1.46) kJ/mol by the Hess thermochemical cycle. In addition, the reliability of the designed thermochemical cycle was verified by UV-Vis spectroscopy and refractive indexes.