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

摘要

A coordination compound of erbium perchlorate with L-alpha-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 275-296 K,which was ascribed to a solid-to-solid phase transition according to the results of TG/DTG analysis.The temperature T_(tr),the enthalpy DELTA_(tr)H_m and the entropy DELTA_(tr)S_m of the phase transition for the compound were determined to be,T_m =(283.315 ± 0.061)K,(11.026 ± 0.059)kJ mol~(-1)and(38.918 ± 0.206)J K~(-1)mol~(-1).Two polynomial equations of heat capacities as a function of the temperature in the regions of 78-275 K and 296-372 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 DELTA_fH_m~°=-(7794.40+1.01)kJ mol~(-1),by an isoperibol solution-reaction calorimeter.