The article presents the results of studying newly synthesized europium and terbium (III) complexes with terephthalic acid using X-ray, elemental, IR spectroscopic and derivatographic analysis. The chemical formulas of the complexes, the coordination form of terephthalic acid, as well as the processes of thermal decomposition and formation of isostructural supramolecular coordination compounds are established. It is also established that, despite the same compositions and structures, the thermal decomposition of these compounds occurs differently, which is explained by the nature of the metals and the stereochemistry of the ligands.