Thermodynamic investigation on the reactions of formation of the compounds RE(C5H8NS2)3(C12H8N2) (RE = Eu, Tb)

The reactions of ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen · H2O) by hydrated lanthanide chlorides in the presence of absolute ethanol yield two novel lanthanide derivatives represented with the empirical formula RE(PDC)3(phen) (RE = Eu, Tb). The resulting compounds were characterized by elemental analysis, TG-DTG and i.r. spectrum. The enthalpy change of the reaction of complex formation from a solution of the reagents, ΔrHmθ(l), and the molar heat capacities of the compounds, cm, were determined at T = 298.15 K by using an RD496-III heat conduction microcalorimeter, which were (−22.21 ± 0.08) kJ · mol−1 and (61.68 ± 0.65) J · mol−1 · K−1 for Eu(PDC)3(phen) and (−21.04 ± 0.05) kJ · mol−1 and (67.74 ± 0.60) J · mol−1 · K−1 for Tb(PDC)3(phen), respectively. On the basis of the appropriate thermochemical cycles and other auxiliary thermodynamic data, the enthalpy changes of formation of the compounds from the reactions of the regents in solid phase, ΔrHmθ(s), were calculated as being (54.53 ± 0.31) kJ · mol−1 for Eu(PDC)3(phen) and (40.20 ± 0.36) kJ · mol−1 for Tb(PDC)3(phen). The thermodynamics of reactions of formation of the compounds were investigated by the reactions in ethanol. Fundamental parameters, the activation enthalpy (ΔH≠θ), the activation entropy (ΔS≠θ), the activation free energy (ΔG≠θ), the apparent reaction rate constant (k), the apparent activation energy (E), the pre-exponential constant (A) and the reaction order (n), were obtained by combination of the thermochemical data of the reaction and kinetic equations with the data of thermokinetic experiments.