Treatment of chloride rare earth (RE＝La, Pr, Nd, Sm～Lu) hydrate with sodium diethyldithiocarbamate (NaEt₂dtc) and 1,10-phenanthroline (phen) gave rise to thirteen complexes with an empirical formula RE(Et₂dtc)₃(phen). IR spectra of the resulting complexes showed that two sulfur atoms in NaEt₂dtc and two nitrogen atoms in phen coordinate to RE in bidentate fashion, respectively. The enthalpies of solution of rare-earth chloride hydrate, NaEt₂dtc and phen in ethanol were measured by an RD-496 Ш microcalorimeter at 298.15 K, together with the mixing enthalpy of ethanol solution of NaEt₂dtc and phen and the enthalpies of reaction of formation of the title complexes in ethanol. The enthalpies of reaction of formation of the title complexes in solid were available through a rationally thermochemical cycle. Using the same microcalorimeter, a model was developed for calculating the special heat capacity and the corresponding special heat capacities of the complexes at 298.15 K were determined. The constant-volume energies of combustion of the complexes were measured by an RBC-II rotating-bomb calorimeter, and the standard molar enthalpies of combustion and the standard molar enthalpies of formation were calculated. The thermochemical properties, including the enthalpies of solution of chloride rare earth hydrate in ethanol, the enthalpies of reaction of formation of the title complexes in ethanol or in solid, the special heat capacities at room temperature, the standard molar enthalpies of combustion and the standard molar enthalpies of formation for this series of complexes versus the atomic numbers of rare earth, presented triplet effect, which is representative of certain covalent bond between RE and the ligands and the result of 4f electron to be not shielded fully by 5s5p.

Key words: rare earth sulfocompound, thermochemical property, triplet effect, regularity