Análise estrutural de complexos metálicos derivados do ácido 4-amino-2-hidroxibenzóico

Abstract

In this work have been performed structural elucidation and electronic investigations of two new coordination complexes derived from the 4-amino-2-hidroxybenzoic acid, where the studied ions were Zn2+ and Cu2+. In these investigations experimental and theoretical studies have been done. The experimental techniques used were: spectroscopic techniques (infrared spectroscopy, electronic spectroscopy and Raman scattering), thermogravimetric analysis, atomic absorption and X ray diffraction techniques (single crystal and powder). Theoretical simulations were performed under Density Functional Theory (DFT) using boundary periodic conditions and basis set expanded in plane waves, within the ultrasoft pseudopotential aproximation to describe the inner shell electrons and the GGA-PBE exchange-correlation functional. Themogravimetric analysis showed the presence of four water molecules and through atomic absorption have been determined four cations per molecular formula. Spectroscopic data suggest a possible coordination by the oxygen atom of the carboxylate group, due to the shift of the CO stretching, confirmed by single crystal X ray diffraction (DRX). The single crystal DRX showed that the Zn2+ and Cu2+ complexes are isostructural. Besides the coordination through the oxygen atom of the carboxylate group, there is also coordination by the nitrogen atom of the amine group. The coordination sphere is fulfilled by a water molecule forming a distorted square base pyramidal geometry in the cation center. It is possible to note through single crystal DRX data the formation of a 2D polymer along the ac crystallographic plane, with hydrogen bonds interaction between the 2D polymer sheets (along the b crystallographic axis) as stabilizing interaction to form a 3D polymeric structure. Through DFT calculations the energetic difference between the valence and conduction bands were estimated, classifying the Zn2+ complex as insulator and the Cu2+ complex as semi-conductor. These theoretical results present a good agreement with the experimental ones (diffuse reflectance), showing that the use of theory can be a useful tool in interpretation and prevision of experimental results.