Synthesis, Structural Characterization, and Thermochemistry of Zinc Hydrogen Pyridine 2,6-Dicarboxylate

Abstract

Zinc hydrogen pyridine 2,6-dicarboxylate trihydrate (Zn(HDPC)2 · 3H2O) was synthesized. The composition and crystal structure of the complex were determined by chemical analysis, elemental analysis, and X-ray crystallography. Low-temperature heat capacities of the complex were measured with a small sample automated adiabatic calorimeter over the temperature range from 78 K to 379 K. The experimental heat capacities of the complex were fitted by the least-squares method, and a polynomial equation of experimental molar heat capacities versus reduced temperature was obtained. The smoothed molar heat capacities and thermodynamic functions of the complex relative to the standard reference temperature 298.15 K were calculated based on the fitted polynomial equation. A reasonable thermochemical cycle was designed, and 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. The enthalpy change of the synthesis reaction of the titled compound was calculated to be −(15.95 ± 0.43) kJ · mol−1. Eventually, the standard molar enthalpy of formation of the title complex was derived to be −(2582.60 ± 3.02) kJ · mol−1 by the Hess thermochemical cycle. In addition, the reliability of the designed thermochemical cycle was verified by UV–Vis spectroscopy.