Low-temperature Heat Capacities and Thermodynamic Properties of Crystalline 2-Aminopyridinium Benzoate (C12H12N2O2) (s)

2-Aminopyridinium benzoate was synthesized. Chemical analysis, elemental analysis, and X-ray crystallography were applied to characterize the composition and crystal structure of the compound. The lattice potential energy of the title compound was calculated to be U-POT = 284.297 kJ mol(-1). Low-temperature heat capacities of the compound were measured by a precision automatic adiabatic calorimeter over the temperature range from 78 K to 365 K. A polynomial equation of heat capacities against the temperature in the region of 78 K to 365 K was fitted by a least square method. Based on the fitted polynomial equation, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15 K were calculated at intervals of 5 K. According to the synthesis reaction, the standard molar enthalpies of dissolution for the reactants and product in the selected solvent were measured by an isoperibol solution-reaction calorimeter, respectively. Accordingly, the enthalpy change of the synthesis reaction was calculated to be Delta H-r(m)o = -(20.016 +/- 0.182) kJ mol(-1). Finally, the standard molar enthalpy of formation of 2-aminopyridinium benzoate was determined to be Delta H-f(m)o = -(365.416 +/- 0.961) kJ mol(-1) in accordance with Hess law.