Low-temperature heat capacity and thermodynamic properties of [Re 2(Ile) 4(H 2O) 8](ClO 4) 6 (Re=Nd, Er, Ile=isoleucine)

Abstract

The heat capacities of two kinds of rare-earth element solid complexes with isoleucine [Re 2(Ile) 4(H 2O) 8](ClO 4) 6 (where Re=Nd, Er, and Ile=isoleucine) have been measured by an automatic adiabatic calorimeter in the temperature range from 80 to 370 K. Two solid–solid phase transitions were found from the C p curve of Nd formed complex in the range of 165–175 K with a peak temperature of 167.88 K and in the range of 195–210 K with a peak temperature of 202.13 K. The corresponding molar enthalpies of these phase transitions were determined to be 404.61 J mol −1 and 2.955 kJ mol −1, respectively. One solid–solid phase transition was found for the Er formed complex in the range of 190–205 K with a peak temperature of 193.42 K. The corresponding molar enthalpy of this transition was 14.11 kJ mol −1. Smooth heat capacities and thermodynamic functions relative to the standard state (298.15 K), H T − H 298.15, S T − S 298.15 and −[ G T − G 298.15], of the two compounds, were calculated on basis of experimental heat capacity data. Possible mechanisms of thermal decompositions for the pair of compounds were suggested according to the thermogravimetric (TG) analysis.