Síntese e caracterização: uma abordagem termogravimétrica, espectroscópica e estrutural de complexos de lantanídeos trivalentes La(III), Ce(III) e Pr(III) com um ligante monocarboxilato

Abstract

In the present study three lanthanide complexes (La, Ce and Pr) were synthesized and characterized as crystalline powder in the solid state. The lanthanum complex was obtained in the hydrated form and the cerium and praseodymium in anhydrous form, which can be simplified by the general formula [Ln (DMB)3] with Ln representing the trivalent lanthanide ions and DMB the monocarboxylate 3,5 -dimethoxybenzoate already deprotonated. Syntheses of the complexes were performed by stoichiometric addition of the binder solution 3,5-dimethoxybenzoate under stirring to solutions of the respective lanthanide chlorides or nitrates. The precipitates obtained were washed, isolated and dried at the same temperature, prior to all analyzes. For the characterization, the following techniques were used: X-ray powder diffractometry (XRD) and refinement by the Rietveld method, absorption spectroscopy in the infrared region with Fourier transform and attenuated total reflectance (FT-IR/ATR), thermoanalytical techniques such as thermogravimetry and simultaneous differential scanning calorimetry (TGA-DSC), analysis of the evolved gases (EGA) using the coupled (TGA-DSC/FT-IR) techniques. In addition to these characterizations a previous study of fluorescence was also carried out. With these results it was possible to elucidate the stoichiometric ratio of the complexes as being 1:3 metal:ligants, whereas the crystal structures were obtained in the form of a polymer network in which the coordination mode obtained was that the binders act as chelator and as bridge of the binder. From the study of fluorescence it is observed that the lanthanum as it presents fluorescence, as expected, cerium acts as a fluorescence suppressor and the praseodymium complex dissociates the emission to the red region.