Abstract: Low-temperature heat capacities of the complex Zn(Phe)(NO3)2·H2O(s) (Phe: phenylalanine) have been precisely measured with a small sample precision automated adiabatic calorimeter over the temperature range from 78 to 370 K. The initial dehydration temperature of the complex (T0=(324.27±0.37) K) has been obtained by means of the analysis of the heat capacity curve. The experimental values of molar heat capacities have been fitted to a polynomial equation of heat capacities (Cp, m) vs the temperature (T) with the least square method. The smoothed heat capacities and the thermodynamic functions of the complex have been calculated on the basis of the equation. In accordance with Hess law, dissolution enthalpies of the mixtures {ZnSO4·7H2O(s)+2NaNO3(s)+L-Phe(s)} and {Zn(Phe)(NO3)2·H2O(s)+Na2SO4(s)} in 2 mol·L-1 HCl were measured to be: ⊿dH0m,1=(69.42±0.05) kJ·mol-1 and ⊿dH0m,2 =(48.14±0.04) kJ·mol-1, by using an isoperibol solution-reaction calorimeter. Furthermore, the standard molar enthalpy of formation for the complex was determined as, ⊿fH0m =-(1363.10±3.52) kJ·mol-1, by designing a thermochemical cycle. In addition, the reliability of the designed thermochemical cycle has been verified by UV-Vis spectroscopy and the data of the refractive indices.

Key words: Zn(Phe)(NO3)2·H2O(s), Adiabatic calorimetry, Low-temperature heat capacity, Solution-reaction calorimetry, Standard molar enthalpy of formation