配合物Zn(Phe)(NO3)2·H2O(s)的低温热容和标准摩尔生成焓

利用精密自动绝热热量计直接测定了配合物Zn(Phe)(NO3)2·H2O(s) (Phe:苯丙氨酸)在78-370 K温区的摩尔热容. 通过热容曲线的解析得到该配合物的起始脱水温度为, T0=(324.27±0.37) K. 将该温区的摩尔热容实验值用最小二乘法拟合得到摩尔热容(Cp, m)对温度(T)的多项式方程, 并且在此基础上计算出了它的舒平热容值和各种热力学函数值. 依据Hess定律, 通过设计热化学循环, 选择体积为100 mL浓度为2 mol·L-1 的盐酸作为量热溶剂, 利用等温环境溶解-反应热量计分别测定混合物{ZnSO4·7H2O(s)+2NaNO3(s)+L-Phe(s)}和{Zn(Phe)(NO3)2·H2O(s)+Na2SO4(s)}的溶解焓为, ⊿dH0m,1 =(69.42±0.05) kJ·mol-1, ⊿dH0 m,2 =(48.14±0.04) kJ·mol-1, 进而计算出该配合物的标准摩尔生成焓为, ⊿fH0m =-(1363.10±3.52) kJ·mol-1. 另外, 利用紫外-可见(UV-Vis)光谱和折光指数(refractiveindex)的测量结果检验了所设计的热化学循环的可靠性.

Low-temperature Heat Capacities and Standard Molar Enthalpy of Formation of the Complex Zn(Phe)(NO3)2·H2O(s)

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.