Metal-organic frameworks: síntese, caracterização e aplicação em troca aniônica

Abstract

Metal-organic frameworks (MOFs) are compounds containing metallic centers connected to each other by organic ligands, varying from 0D to 3D dimensions. Most MOFs are neutral or anionic, but cationic species also exist. In order to make this possible, it is necessary a pre-determinate selection of metal and ligands so the positive charge of the metallic ion can overcome the negative or neutral charge of the ligands. Cationic MOFs may contain anions on their pores or channels, which can be exchanged. In this paper, the cationic MOF [Ag(pyz)]NO3 (pyz = pyrazine) was synthesized by a novel methodology and was extensively studied over its anion exchange capacities. Both inorganic and organic anions were tested and the exchange products were characterized by powder X-ray diffraction (PXRD). The studies here described suggest that the [Ag(pyz)]NO3 does not present restrictions about the ions sizes to be incorporated in its framework once both small and large ions were adsorbed. Our work indicates that this MOF can be used to the selective separation of linear organic ligands. This paper also presents the results obtained for different synthetic routes aiming the incorporation of new anions into the complex. Besides the anion exchanges, we also performed hydrothermal and room temperature synthesis with such anions. Hydrothermal processes in a wide range of conditions are also reported for reactions between pyrazine and other metals, such as copper, nickel, cobalt and zinc. Furthermore, this paper presents the synthesis of the recently reported TIPA (tri(4-imidazolyphenyl)amine) ligand and its hydrothermal reactions with copper, zinc and cobalt salts. The products were once again analyzed by PXRD.