Synthesis, Characterization, and Thermodynamic Study of the Coordination Compound Cd(HNic)2Cl2(s)

Abstract

Nicotinic acid and cadmium chloride were used as the reactants, absolute ethanol as solvent, and a novel coordination compound Cd(HNic)2Cl2 was synthesized by the method of liquid phase reaction. Chemical and elemental analyses, FTIR, and X-ray powder diffraction techniques were applied to characterize its composition and structure. Low-temperature heat capacities of the solid coordination compound have been measured by a precision automated adiabatic calorimeter over the temperature range from T = 78 K to T = 400 K. The experimental values of the molar heat capacities in the temperature region were fitted to a polynomial. Smoothed heat capacities and thermodynamic functions of the complex relative to 298.15 K were calculated based on the fitted polynomial and tabulated at 5 K intervals. In accordance with Hess’s law, a reasonable thermochemical cycle was designed based on the preparation reaction of the new substance, and 100 mL of 0.1 M HCl solution was chosen as the calorimetric solvent. 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 liquid phase reaction was determined as ΔrHmo = (23.46 ± 0.30) kJ·mol−1, and the standard molar enthalpy of formation of the complex was determined to be −(1088.8 ± 1.9) kJ·mol−1 by means of the enthalpy change of the reaction and other auxiliary thermodynamic quantities.