Low-temperature heat capacity and thermochemical study of [Re-2(Pro)(6)(H2O)(4)](ClO4)(6) (Re = Nd, Gd; Pro = proline) crystals

The heat capacities of two solid complexes of rare-earth compounds with pro line [Re-2(Pro)(6)(H2O)(4)](ClO4)(6) (Re = Nd, Gd; Pro = proline. C5H9O2N), were measured with a high-precision automatic adiabatic calorimeter over t he temperature range from 78 to 370 K, The heat capacity curves of the two complexes are smooth and similar in magnitude to each other except for a me lting transition of [Gd-2(Pro)(6)(H2O)(4)](ClO4)(6) that occurred in the te mperature range of 340-346 K with a peak temperature of 342.48 +/- 0.01 K, The molar enthalpy and entropy of fusion of [Gd-2(Pro)(6)(H2O)(4)](ClO4)(6) were determined to be 26.104 +/- 0.031 k J mol(-1) and 76.23 +/- 0.08 J K- 1 mol(-1), respectively, on the basis of the heat capacity measurements. Th ermal decompositions of the two complexes were studied through the thermogr avimetry (TG) experiments and possible mechanisms of the decompositions wer e suggested according to the TG analysis. The molar combustion energies of the two complexes were determined to he 17010 +/- 1.6 and 15630 +/- 1.5 J m ol(-1) For [Nd-2(Pro)(6)(H2O)(4)](ClO4)(6) and [Gd-2(Pro)(6)(H2O)(4)](ClO4) (6), respectively, by means of oxygen-bomb calorimetric measurements. (C) 2 001 Elsevier Science B.V. All rights reserved.