Thermochemical Study of the Solid Complexes Ln[(CH₃)₂NCS₂)]₃(C₁₂H₈N₂) (Ln = Eu, Gd, Tb, Dy)

Four solid complexes Ln(Me₂dtc)₃(phen) (Ln = Eu, Gd, Tb, Dy) have been prepared from the reactions of hydrous lanthanide chloride, sodium dimethyldithiocarbamate (NaMe₂dtc), and 1,10-phenanthroline (phen·H₂O) in anhydrous ethanol. The title complexes were characterized by elemental analysis, IR spectroscopy, TG−DTG−DSC, and X-ray diffraction analysis. Their enthalpy changes of liquid-phase reactions of formation, Δ_rH_m^θ(l), were determined at 298.15 K by a microcalorimeter, and the enthalpy changes of the solid-phase reactions of formation, Δ_rH_m^θ(s), were calculated on the basis of a thermochemical cycle. The thermodynamics of reactions of formation of the complexes were studied via the reactions in solution. Combining the thermochemical data of the reactions and kinetic equations with the data of thermokinetic experiments, fundamental thermodynamic and kinetic parameters were achieved. The molar heat capacities of the title complexes were determined using an improved RD496-III type microcalorimeter at 298.15 K.