MOFs with PCU Topology for the Inclusion of One-Dimensional Water Cages: Selective Sorption of Water Vapor, CO₂, and Dyes and Luminescence Properties

Abstract

A rigid pyridine-3,5-bis(5-azabenzimidazole) ligand (L) and linear dicarboxylate sodium terephthalate (TPA) with Cd(II), Zn(II), and Co(II) under solvothermal conditions afforded water stable and nitrogen-rich MOFs with general formulas [Cd2L2(TPA)2]·12H2O}n, 1, {[Zn4L4(TPA)4]·(DMF)·16H2O}n, 2, and {[Co2L2(TPA)2]·12H2O}n, 3, respectively. These MOFs are found to contain doubly interpenetrated pcu networks with hydrophilic channels. The networks are propagated by M2(CO2)2 SBUs (intermetallic distances 4.0 Å) which leads to the formation of a two-dimensional grid structure of metal-terephthalate. The shape of grids varies from rhomboidal to squaric depending on the presence of a metal center. The channels of these MOFs are occupied by the one-dimensional water cages. In the pcu network, each cuboid is found to have dimensions of ∼12.5 Å as width and 18.5 Å as length. They have shown an excellent ability for water vapor sorption (180–225 cc/g at 298 K). Further, CO2 is found to be the preferred sorbent (70 cc/g at 273 K) over N2. They were also shown to be capable of dye (methylene blue and crystal violet) removal from aqueous solutions through adsorption. Further, Cd(II) and Zn(II) MOFs are found to exhibit solid state luminescence properties.