Low-temperature heat capacities of [Er2(l-Glu)2(H2O)6](ClO4)4·6H2O(s)

A coordination compound of erbium perchlorate with l-α-glutamic acid, [Er2(l-Glu)2(H2O)6](ClO4)4·6H2O(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 from 78 to 318 K. An endothermic peak in the heat-capacity curve was observed over the temperature region of 290–316 K, which was ascribed to a solid-to-solid phase transition. The temperature Ttrans, the enthalpy ΔtransHm and the entropy ΔtransSm 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.