Avaliação cristalográfica do ligante ácido kójico e de seus compostos de coordenação [Fe(Kj)3] e [Ca(Kj)4]

Abstract

This work has as objective to contribute to a better understanding of the kojic acid coordination chemistry through the analysis of crystallographic data, lengths of bonds and angles, for the free ligand and coordinated in a bidentate way to metal ions Fe3+ and Ca2+, originating respectively the homoleptic complexes [Fe(Kj)3] and [Ca(Kj)4]. The crystallographic data of the ligand and its complexes were analyzed evaluating the coordination influence on kojic acid chemical bonds. The results showed that the free kojic acid generally has smaller bonds lengths than when covalently bound to the metal center. This effect is due to changes in electronic density over the ligand as result of coordination to the metal. The equatorial and axial angles found for the complexes [Fe(Kj)3] and [Ca(Kj)4] presented values not expected for the respective geometries, thus indicating that the bidentate coordination environment of the kojic ligand induces distortion of the geometry. The results of the analysis led to observation of the similarities and differences between the coordination compounds, which showed oxidation state and numbers of ligands present in the different coordination sphere, but also different geometries.