Synthesis, crystal structure and thermochemistry of the coordination compound of pyridine-2,6-dicarboxylic acid with barium ion

• Crystal structure of the complex of pyridine 2,6-dicarboxylate barium is determined.
• Low-temperature heat capacities of the compound were measured.
• Smoothed molar heat capacities and thermodynamic functions were calculated.
• The enthalpy change of the synthesis reaction was obtained.
• Standard molar enthalpy of formation was determined.

The complex of pyridine 2,6-dicarboxylate with Ba2+ ion Ba(HDPC)2·2H2O(s) was synthesized. X-ray crystallography was applied to characterize the crystal structure of the complex. Low-temperature heat capacities of the complex were measured with an automated adiabatic calorimeter in the temperature range from 78 to 360 K. A polynomial equation of experimental molar heat capacities as a function of the temperature was obtained by the least-squares method. The smoothed heat capacities and thermodynamic functions of the complex were calculated based on the fitted polynomial equation. In addition, the standard molar enthalpies of dissolution for the reactants and products of the synthesis reaction in a selected solvent were measured by an isoperibol solution-reaction calorimeter, and the standard molar enthalpy of formation of the title complex was calculated as – (2993.0 ± 3.0) kJ mol−1 by the Hess thermochemical cycle. Furthermore, the reliability of the designed thermochemical cycle was verified by UV–vis spectroscopy.

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