Thermal study, temperature diffraction patterns and evolved gas analysis during pyrolysis and oxidative decomposition of novel ternary complexes of light lanthanides with mefenamic acid and 1,10-phenanthroline

Abstract

New ternary lanthanide complexes with mefenamic acid (Hmef) and phenanthroline with the stoichiometry Ln2(mef)5(phen)(OH)·nH2O (Ln = La and Ce) and Ln2(mef)4(phen)(OH)2·nH2O (Ln = Pr, Nd, Sm, Eu and Gd) were synthesized and fully characterized by an elemental analysis, infrared spectroscopy, powder X-Ray diffraction (PXRD), combined thermogravimetry and differential scanning calorimetry (TG-DSC) in air and nitrogen atmospheres, evolved gas analysis by combined TG-FTIR-MS techniques as well as temperature controlled X-ray diffraction.The PXRD data suggest that the compounds are crystalline or amorphous and no isomorphic series were obtained. The FTIR spectra suggested the coordination of the lanthanide ions by the bidentate carboxylate groups of mefenamates as well as nitrogen atoms of phenanthroline.The thermal decomposition pathways of the complexes depended on the metal center and differed in air atmosphere and nitrogen atmosphere. From the temperature diffraction patterns, it was experimentally confirmed that in-air degradation of the complexes proceeded with the formation of various lanthanide oxycarbonates as intermediate solids and the decomposition was completed up to 1000 °C with the formation of the appropriate lanthanide oxides as a final solid product. It was proved that during degradation of the tested compounds in nitrogen atmosphere, a mixture of lanthanide oxide, lanthanide oxycarbonate, and soot is formed as an intermediate solid product at around 800 °C and pyrolysis is not finished for all compounds up to 1000 °C. The main gaseous products released during the thermal decomposition of these compounds were water vapor, carbon dioxide, carbon monoxide, nitrogen oxide and ammonia (in air atmosphere), as well as water vapor, carbon oxides, ammonia and a mixture of hydrocarbons from mefenamate ligand degradation (in nitrogen atmosphere).