Síntese e caracterização de trinucleares homo- e heterometálicos baseados em ferro(III) e cobalto(II) para aplicação como blocos construtores em polímeros de coordenação

Abstract

Constantly, the synthetic inorganic chemistry has been playing an important role in the synthesis and characterization of new high-performance inorganic materials which exhibit increasingly specific behaviors. A very promising class of these new inorganic materials are the so-called "Coordination Polymers" (CPs). These compounds are formed by metallic ions coordinated to organic ligands that have divergent coordination points favoring the polymeric growth. The large plurality of combinations of ions and ligands and the variety of arrangements of these interactions form extended structures which can be uni-, bi- or three-dimensional. The porosity, rigidity and the presence of paramagnetic centers in these species are some examples of characteristics that can be explored in order to carry out studies in applications such as: catalysis, adsorption, gas storage and development of magnetic and optoelectronic devices. In some cases, the CPs are obtained by incorporating Building Blocks of lower nuclearity, which are also called Secondary Building Units (SBUs). The SBUs can be formed by inorganic clusters such as trinuclear oxo-complexes that permit better control of the porosity and directionality of the polymer self-assembly; thereby, it is possible to perform more rationalized synthetic procedures, with the possibility of topological prediction of the structure. Therefore, this work aims the synthesis and characterization of two potential SBUs based on trinuclear oxo-complexes, one of which is homometallic based on iron(III), product B, and another heterometallic based on iron(III) and cobalt(II), product C. This last one is obtained by using a cobalt(II) coordination polymer, product A, as one of the starting materials. The three structures were synthesized for the first time in this work and their characterizations were performed with the aid of techniques such Single-crystal X-ray Diffraction (SC-XRD), Powder X-Ray Diffraction (P-XRD), dosage of the contents of C, H, N and metals (by atomic absorption and by spectrophotometric analysis), absorption in the ultraviolet and visible region (UV/Vis), electronic paramagnetic resonance (EPR) and absorption in the infrared region (IV) spectroscopies. The structural analyzes performed by SC-XRD revealed low R factor values for the three structures, which indicates good correlation between the proposed structural models and the experimental electron density distributions of the unit cells. The spectroscopic analysis give support for the structures revealed by SC-XRD and the purity of the three products was confirmed by comparing the theoretical and experimental data relative to the percentages of C, H, N and metals and by comparing theoretical and experimental P-XRD data. The two oxo-complexes are obtained in moderate yields, which make them feasible for use as SBUs in the preparation of higher nuclear aggregates.