稀土钬丙氨酸配合物的热力学性质

摘要

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 ℃ 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.%合成了稀土氯化钬丙氨酸配合物, [Ho2(Ala)4(H2O)8]Cl6,的晶体 .用绝热量热法测定了其在 78～ 363 K温区的热容 .在 214～ 255 K温区发现一固-固相变,相变峰温、相变焓和相变熵分别为 235.09 K, 3.017 kJ@ mol- 1和 12.83 J@ K- 1@ mol- 1.用最小二乘法将实验热容值拟合成热容随温度变化的多项式方程 ,利用此方程式和热力学函数关系 ,计算出以 298.15 K为参考温度的热力学函数值 .在 40～ 800 ℃温区,用热重分析和差示扫描量热法研究了该配合物的热稳定性,观察到 [Ho2(Ala)4(H2O)8]Cl6分两步分解,第一步从 80 ℃开始, 179 ℃结束;第二步从 242 ℃开始, 479 ℃结束 .从热分析结果推测出该配合物可能的热分解机理 .