Liu Bei-Ping

Thermodynamic Properties of [Ho 2 (Ala) 4 (H 2 O) 8 ]Cl 6 (Ala=alanine)

The crystalline complex of holmium chloride with alanine, [Ho2(Ala)4(H2O)8]Cl6, was synthesized. Heat capacities of [Ho2(Ala)4(H2O)8]Cl6, were measured by adiabatic calorimetry over the temperature range from 78 to 363 K. A solid-solid phase transition was found between 214 K and 255 K with the peak temperature of 235.09 K. The enthalpy and entropy of the transition were determined to be 3.017 kJ•mol^(-1) and 12. 83 J•K^(-1)•mol^(-1), respectively. The molar heat capacities were presented by a fitted polynomial as a function of reduced temperature. The thermodynamic functions relative to the reference temperature 298.15 K were calculated based on the heat capacity data. Thermal stability of the complex was studied by thermogravimetry (TG) and differential scanning calorimetry (DSC) over the temperature range from 40 to 800℃. From the DTG curves, two peaks were observed in the process of the thermal decompositions for the complex. The first mass-loss peak started from 80 t and ended at 179℃, and the second mass-loss peak started from 242℃ and ended at 479℃. A possible mechanism of the thermal decomposition was presented.