Synthesis of Hofmann-based metal–organic frameworks incorporating a bis-pyrazole linker for various gas separations

Abstract

In this work, the synthesis and structural characterisation of two novel Hofmann-based metal–organic frameworks incorporating the angular bis-pyrazole ligand, 4,4′-methylene-bis(3,5-dimethylpyrazole) (H₂mdp), [M(H₂mdp)(Ni(CN)₄)] [M = Co(II), Fe(II)] are reported. The isostructural frameworks possess undulating 2D [MNi(CN)₄] layers linked by H₂mdp ‘pillars’ to form one-dimensional channels lined with unsaturated Ni(II) metal binding sites and methylpyrazole moieties along the pore walls. Single component gas adsorption and IAST calculations, DFT and breakthrough experiments reveal strong binding at unsaturated metal sites and the pore walls, to enable selective uptake of acetylene (C₂H₂) over methane and CO₂; propylene (C₃H₆) over propane; and xenon over krypton. Taken together these data indicate that [M(H₂mdp)(Ni(CN)₄)] show promise for the selective separation of numerous gases.