Nova rota de síntese de um ligante dicarboxílico para obtenção de redes metalorgânicas inéditas com poros de dimensões elevadas

Abstract

Metal-Organic Frameworks (MOFs) stand out as promising porous materials, primarily due to their structural versatility and high adsorption capacity. This work aimed to produce a connector derived from 2,5-dihydroxyterephthalic acid, featuring three aromatic rings between the carboxylic acid groups, using the Suzuki–Miyaura coupling reaction. This modification sought to obtain an extended ligand capable of forming MOFs isoreticular to MOF-74, but with larger pore diameters. The ligand, 3,3''-dihydroxy-2',5'-dimethyl-[1,1':4',1''-terphenyl]-4,4''-dicarboxylic acid, was synthesized through an adaptation of a route already described in the literature. While the original route proposes a sequential construction methodology, the strategy developed in this work enables simultaneous modification of both ends of the substrate, reducing the number of steps from five to four and increasing the overall yield from 57.0% (literature) to 60.2% (proposed). The newly synthesized ligand was then employed in the solvothermal synthesis of MOFs. Three new MOFs were successfully obtained and characterized, incorporating the transition metals Zn(II), Co(II), and Ni(II), resulting in the structures Zn-IRMOF-74-III, Co-IRMOF-74-III, and Ni-IRMOF-74-III, respectively. Structural confirmation of the obtained MOFs was carried out using powder X-ray diffraction and infrared spectroscopy. Furthermore, a systematic investigation was conducted on variables such as the type of metal precursor, the composition of the solvent mixture, and reagent concentrations, identifying the conditions that maximize yield and crystallinity for each MOF produced. The best yields for the IRMOFs were achieved using solvothermal syntheses in solutions containing a DMF–ethanol mixture (87.5/12.5 v/v) and the acetates Zn(CH₃COO)₂, Co(CH₃COO)₂, and Ni(CH₃COO)₂. The highest crystallinity was obtained with the same solvent mixture but using Zn(NO₃)₂, CoCl₂, and Ni(NO₃)₂ as metal precursors. This study contributed to the development of a novel and more cost-effective synthesis route for the ligand, the production of new IRMOF-74-III materials, and the implementation of a protocol for miniaturizing solvothermal reactors, optimizing reagent consumption and providing greater flexibility for varying experimental parameters.