文摘
Fourteen rare earth complexes with pyromellitic acid were synthesized and characterized by means of chemical and elemental analysis, and TG–DTG. The constant-volume combustion energies of complexes, ΔcU, were measured by a precise rotating-bomb calorimeter (RBC-type II). Their standard molar enthalpies of combustion, , and standard molar enthalpies of formation, , were calculated at T = 298.15 K. The relationship of and with the atomic numbers of the elements in the lanthanide series was examined. The results show that a certain amount of covalence is present in the chemical bond between rare earth cations and the ligand.