Complexos de ferro e manganês com derivados da base de Schiff salen e ligantes carboxilatos

Abstract

Salen Schiff base complexes have been highlighted both as antitumor agents, catalysts and modified electrodes. Thus, the present work has the objective to synthesize new iron(III) and manganese(III) complexes containing as main ligand the salen base Schiff derivaties, 3-MeOsalen or 3-MeOsalophen, and the salicylate and biphthalate carboxylate ligands as auxiliaries. The synthesized ligands, precursors complexes and the novel synthesized carboxylate complexes were characterized by spectroscopic techniques (Vibrational spectroscopy in the infrared region, Raman Spectroscopy, Electronic spectroscopy in the ultraviolet and visible region and fluorescence), electrochemistry (cyclic voltammetry) and thermal analysis (Thermogravimetry). The complexes presented asymmetric and symmetrical vibrational modes of the carboxylate group, for salicylates, observed in 1570 cm-1 (υasCO2 - ) and 1370 cm-1 (υsCO2 - ) while the spectra of the complexes with biphthalate, the υasCO2 - were observed in around 1700 cm-1 and υsCO2 - around 1350 cm-1 . By the variation of these stretches, the ligands are coordinated in bidentent form. In relation to the electronic spectra for the carboxylate iron complexes, bathochromic displacement of the LMCT charge transfer band was verified and in the manganese complexes changes in the d-d bands were observed, having as reference the respective precursor complexes. These changes were due to substitution of the chloride ligand by the carboxylate ligand. In the emission spectra of the iron complexes with 3-MeOsalophen ligand, they presented an emission band around 480 nm. In the voltamograms of the complexes was observed a metal redox pair Fe3+/Fe2+ ou Mn3+/Mn2+ and processes related to the Schiff base. In replacing the chloride ligand in precursors complexes by the carboxylate caused an increase in difference of the cathodic potential and the anodic potential of the metal. In the TG and DTG curves have been observed the decomposition of the carboxylate ligand at around 262°C and the other two losses attributed to Schiff's base.