Synthesis, spectral and thermal study of La(III), Nd(III), Sm(III), Eu(III), Gd(III) and Tb(III) complexes with mefenamic acid

New binuclear complexes of La(III), Nd(III), Sm(III), Eu(III), Gd(III) and Tb(III) ions with mefenamic acid were obtained in solid phase. For all compounds considered, complexation occurs at pH 6–6.5. The analyzed complexes were characterized on the basis of chemical and elemental analyses, molar conductance, UV–Vis, IR and 1H NMR spectroscopies as well as thermoanalytical techniques. According to the research results, the molecular formula of the complexes is Ln2(C15H14NO2)3(OH)3×nH2O, with the exception of the La(III) complex which has the formula La2(C15H14NO2)5(OH). The results show that only the carboxyl group is involved in the coordination of the rare earth ions in the bidentate mode. Coordination does not occur through the nitrogen atom. All the complexes are soluble in DMSO, and they are nonelectrolytes. The TG-FTIR technique was employed in order to study a decomposition pathway of the obtained compounds. The received results provide information on the composition, thermal stability, thermal decomposition, as well as the gaseous products that evolved during the thermal decomposition of the considered compounds.