Low-Temperature Heat Capacity and Thermodynamic Functions of Ho(NO3)3(C2H5O2N)4•H2O

A complex of a rare-earth metal (Ho) nitrate with glycine (C2H5O2N), Ho(NO3)(3)(C2H5O2N)(4)center dot H2O, was synthesized, and characterized by chemical analysis, elemental analysis, and infrared (IR) spectroscopy. The thermodynamic properties of the complex were also studied. The low-temperature molar heat capacities at constant pressure (C-p,C-m) of the complex were measured using a high-precision automatic adiabatic calorimeter over the temperature range from 80 to 390 K. The experimental molar heat capacities at constant pressure were used to deduce the polynomial equations for the heat capacity as a function of reduced temperature by applying the least-squares method to the two smooth stages of the curve. Based on the thermodynamic relationships among heat capacity, entropy, and enthalpy, the thermodynamic functions (H-T,H-m - H-298.15,H-m) and (S-T,S-m - S-298.15,S-m) were derived from the heat capacity data, with temperature intervals of 5 K. The molar enthalpy and entropy changes of the transition process at about 350 K (Delta H-trs(m) and Delta S-trs(m)) were calculated from the heat capacity curve. The thermal stability of the complex was determined using differential scanning calorimetry (DSC).