Low-temperature Heat Capacities and Thermochemistry on the Complex of Erbium Perchlorate with L-α-Glycine [Er2(L-Gly)2(H2O)12](ClO4)6 4H2O(s)

You-Ying Dia,* and Zhi-Cheng Tanb
a College of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng 252059, Shandong Province, P. R. Cnina
b Thermochemistry Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, P. R. China
* Corresponding author: Tel: +86-635-8538299, Fax: +86-635-8239121
E-mail: yydi@lcu.edu.cn, diyouying@126.com

A coordination compound of erbium perchlorate with L-α-glycine, [Er2(Gly)2(H2O)12] (ClO4)6 4H2O(s), was synthesized. By chemical analysis, elemental analysis, FTIR, TG/DTG, and comparison with relevant literature, its chemical composition and structure were established. The purity was found to be >99.0%, without melting point. Low-temperature heat capacities were measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 372 K. An obvious endothermic peak in the heat capacity curve was observed over the temperature region of 275296 K, which was ascribed to a solid-to-solid phase transition according to the results of TG/DTG analysis. The temperature Ttr, the enthalpy ∆trHm and the entropy ∆trSm of the phase transition for the compound were determined to be, Ttrs = (283.315 0.061) K, (11.026 0.059) kJ mol1 and (38.918 0.206) J K1 mol1. Two polynomial equations of heat capacities as a function of the temperature in the regions of 78275 K and 296372 K were fitted by the least square method, respectively. The mechanism about thermal decomposition of the complex was deduced on the basis of the TG/DTG analysis. In accordance with Hess law, the standard molar enthalpy of formation for the complex was determined
as ∆fHmo= (7794.401.01) kJ mol1, by an isoperibol solution-reaction calorimeter.

Keywords: Complex of erbium perchlorate with L-α-glycine; Adiabatic calorimetry; Low-temperature heat capacity; Isoperibol solution-reaction calorimetry; Standard molar enthalpy of formation