Low-Temperature Heat Capacities and Thermochemistry on the Complex of Samarium Perchlorate with L-alpha-Valine Acid: [Sm-2(L-alpha-Val)(4)(H2O)(8)](ClO4)(6)

A complex of samrium perchlorate with L-alpha-Valine acid, [Sm-2(L-alpha-Val)(4)(H2O)(8)](ClO4)(6), was synthesized by the reaction of samarium perchlorate and L-alpha-Valine acid in distilled water. The title complex was characterized by chemical analysis, elemental analysis, FTIR and TG/DTG. Low-temperature heat capacities were measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 371 K. A polynomial equation of heat capacities as a function of the temperature was fitted by the least-squares method. Based on the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the complex relative to the standard reference temperature 298.15 K were calculated with the interval of 5 K. The possible mechanism about thermal decomposition of the complex was deduced on the basis of the TG/DTG analysis. A reasonable thermochemical cycle was designed on the basis of the Hess law, and the standard molar enthalpies of dissolution for the reactants and products of the designed reaction in the selected solvents were measured by an isoperibol solutionreaction calorimeter, respectively. In addition, the enthalpy change of the reaction was determined to be Delta H-r(m)circle minus = (24.83 +/- 0.85) kJ.mol(-1) from the data of the above standard molar enthalpies of dissolution. Eventually, the standard molar enthalpy of formation of the complex was derived to be -(8 010.01 +/- 3.90) kJ.mol(-1) by the combination of the enthalpy change of the reaction with other auxiliary thermodynamic quantities