Low-Temperature Heat Capacity and Enthalpy of Formation of [Er2(Gly)6(H2O)4](ClO4)6·5H2O

A crystalline complex of erbium perchlorate coordinated with glycine, [Er2(Gly)6(H2O)4](ClO4)6·5H2O, has been synthesized. No melting point is observed above room temperature. The heat capacity of the complex was measured by adiabatic calorimetry from 79 K to 369 K, and two peaks centered at 233 K and 325 K were found. The first peak centered at 233 K was a phase transformation peak, and the second was decomposition. The temperature, enthalpy change, and entropy change of the phase transformation were 219.47 K, 17.51 kJ·mol-1, and 79.77 J·K-1·mol-1, and those of the decomposition process were 312.576 K, 94.86 kJ·mol-1, and 303.49 J·K-1·mol-1. The polynomial equations of heat capacity in different temperature ranges, 79.091 K to 217.424 K and 255.606 K to 306.143 K, have been obtained by least-squares fitting. The standard enthalpy of formation was determined to be ΔfHmθ ([Er2(Gly)6(H2O)4](ClO4)6·5H2O, s, 298.15 K) = −7911.13 ± 2.77 kJ·mol-1 by isoperibol reaction calorimetry.