Construction of two novel non-penetrating Co-MOFs derived from designed 2,4,6-tri(2,4-dicarboxyphenyl)pyridine: synthesis, structure and gas adsorption properties

Abstract

The strategy of extending ligands and reducing symmetry provides facile access to obtain a wide variety of linkers for the construction of MOFs bearing diverse structures and intriguing properties. In this work, we employed this strategy to design and prepare a 2,4,6-tri(2,4-dicarboxyphenyl)pyridine ligand and used it to successfully construct two cobalt-based MOFs with the formula [(NH₂Me₂)₂][Co₂(tdp)]·2DMA·2H₂O (Co-MOF 1) and [(NH₂Me₂)₂][Co₇(μ₃-OH)₄(tdp)₂(H₂O)₆]·2DMA·3H₂O (Co-MOF 2) (H₆tdp = 2,4,6-tri(2,4-dicarboxyphenyl)pyridine), which were thoroughly characterized by various techniques including FTIR, TGA, PXRD and single-crystal X-ray diffraction. Both MOFs have non-penetrating network structures. Co-MOF 1 shows a three-dimensional honeycomb structure through sharing Co²⁺. Co-MOF 2 has a nanotube structure formed by bridging a Co₇O cluster with a tdp⁶⁻ ligand. Furthermore, the gas adsorption properties with respect to C₂H₂, C₂H₄, CO₂, and CH₄ were systematically investigated. By comprehensive comparison, Co-MOF 1 is a highly promising material for C₂H₂/CH₄, C₂H₄/CH₄ and CO₂/CH₄ separations. Specifically, the IAST adsorption selectivity at 298 K and 1 atm reaches 25.43, 12.47 and 11.33 for the equimolar C₂H₂/CH₄, C₂H₄/CH₄ and CO₂/CH₄ gas mixtures, respectively. More significantly, as revealed by PXRD, N₂ adsorption measurements and cycle tests, Co-MOF 1 exhibits excellent chemical stability, which lays a good foundation for its practical application.