Heavy trivalent lanthanides and yttrium p-aminobenzoate complexes: synthesis, thermoanalytical and spectroscopic study

Heavy trivalent lanthanide and yttrium complexes with p-aminobenzoate were synthesized and characterized using thermoanalytical, spectroscopic, and complementary techniques. The results provide in-depth knowledge, particularly regarding the thermal behavior of these complexes, which had not been previously reported. Analytical and thermoanalytical data showed that the complexes exhibit a 1:3 metal-to-p-ABA stoichiometry, and FTIR spectra indicated coordination through the carboxylate and amino groups for the Ho(III)-Yb(III), and Y(III) complexes, whereas the lutetium complex showed coordination only by carboxylate group. The complexes exhibited a crystalline structure and, except the lutetium complex, were monohydrated. Simultaneous Thermogravimetric and Differential Thermal Analysis (TG-DTA) and Evolved Gas Analysis (EGA) results allowed investigation of the thermal behavior of the complexes under pyrolytic and oxidative atmospheres. EGA identified CO₂, CO, and NH₃ as the main gaseous products released during thermal decomposition in an air atmosphere, while aniline, CO₂, CO, and NH₃ were identified under a nitrogen atmosphere. Differential Scanning Calorimetry (DSC) enabled the determination of dehydration enthalpies and the study of phase transitions for the Ho(III), Er(III), Y(III) complexes