Thermochemistry on the Complex of Erbium Perchlorate with L ‐ α ‐Glutamic Acid [Er 2 ( L ‐Glu) 2 (H 2 O) 6 ](ClO 4 ) 4 ·6H 2 O(s)

A coordination compound of erbium perchlorate with L‐α ‐glutamic acid, [Er 2 (Glu) 2 (H 2 O) 6 ](ClO 4 ) 4 ·6H 2 O(s), was synthesized. By chemical analysis, elemental analysis, FTIR, TG/DTG, and comparison with relevant literatures, its chemical composition and structure were established. The mechanism of thermal decomposition of the complex was deduced on the basis of the TG/DTG analysis. Low‐temperature heat capacities were measured by a precision automated adiabatic calorimeter from 78 to 318 K. An endothermic peak in the heat capacity curve was observed over the temperature region of 290–318 K, which was ascribed to a solid‐to‐solid phase transition. The temperature T trans , the enthalpy Δ trans H m and the entropy Δ trans S m of the phase transition for the compound were determined to be: (308.73±0.45) K, (10.49±0.05) kJ·mol −1 and (33.9±0.2) J·K −1 ·mol −1 . Polynomial equation of heat capacities as a function of the temperature in the region of 78–290 K was fitted by the least square method. Standard molar enthalpies of dissolution of the mixture [2ErCl 3 ·6H 2 O(s)+2 L ‐Glu(s)+6NaClO 4 ·H 2 O(s)] and the mixture {[Er 2 (Glu) 2 (H 2 O) 6 ](ClO 4 ) 4 ·6H 2 O(s)+6NaCl(s)} in 100 mL of 2 mol·dm −3 HClO 4 as calorimetric solvent, and {2HClO 4 (l)} in the solution A' at T =298.15 K were measured to be, Δ d H m,1 = (31.552±0.026) kJ·mol −1 , Δ d H m,2 = (41.302±0.034) kJ·mol −1 , and Δ d H m,3 = (14.986±0.064) kJ·mol −1 , respectively. In accordance with Hess law, the standard molar enthalpy of formation of the complex was determined as Δ f H ⊖ m = − (7551.0±2.4) kJ· mol −1 by using an isoperibol solution‐reaction calorimeter and designing a thermochemical cycle.