Metal–organic frameworks constructed from a tetrahedral silicon-based linker for selective adsorption of methylene blue

Abstract

The solvothermal assemblies of Cd(II)/Co(II)/Zn(II) ions, a silicon-centered tetrahedral ligand as a principal building block, and a N-donor ancillary ligand yield three metal–organic frameworks, formulated as [Cd₂(H₂O)₂L]·5H₂O·0.5DMF (1), [Co₃O(H₂O)₃L(ttb)]·3H₂O (2), [Zn₃O(H₂O)₂L(ttb)(DMF)₂]·2H₂O (3) [H₄L = 4,4′,4′′,4′′′-silanetetrayltetrabenzoic acid, ttp = 1-(tetrazo-5-yl)-4-(triazo-1-yl)benzene, DMF = N,N-dimethylformamide], respectively. Single-crystal X-ray diffraction analysis demonstrated that all compounds feature three-dimensional structures with different secondary building units. Their permanent porosities were established by the N₂ sorption isotherm at 77 K. The adsorption behavior of 1 towards organic dyes was investigated, revealing rapid and selective separation of methylene blue with a maximum uptake of 1008 mg g⁻¹.