Thermal analysis combined with X-ray diffraction/Rietveld method, FT-IR and UV-vis spectroscopy: Structural characterization of the lanthanum and cerium (III) polycrystalline complexes

In this work, structural, spectroscopical and thermal studies of lanthanum(III) and cerium(III) complexes with the 3,5-dimethoxybenzoate (DMBz) monocarboxylate ligand were performed. The metal-ligand minimum stoichiometry and polymeric arrangement of the complexes were respectively defined by TGA-DSC and X-ray powder diffraction as [M(DMBz)3.n]x, wherein “M” represents the lanthanides, “n” the water molecules in the lanthanum compound and “x” the basic unit of repetition in monoclinic polycrystalline system with space group P21/c. The products of the thermal decomposition of the material were also monitored by TGA-DSC/FT-IR both in air and N2 atmospheres in order to suggest the thermal decomposition mechanism. Theoretical calculations based in experimental results were performed to assess the coordination mode and spectroscopic properties of lanthanide complexes involving a monocarboxylate ligand. From theoretical calculations it was possible to generate FT-IR theoretical vibrational spectra and relate the level of correspondence to the experimental data inherent to the metal-ligand coordination mode. From the HOMO/LUMO orbitals obtained by TD-DFT calculations, the main electronic transitions responsible for the absorption and emission bands of the complexes were determined.