Rotation configuration control of the sp2 bond in the diimidazole–dicarboxylate linker for the isomerism of porous coordination polymers

Abstract

Porous isomers constructed from the same building blocks but different topology break the general preferred coordination rule of organic linkers and metal nodes, representing an invaluable opportunity for enriching their pore chemistry. Herein, a new group of porous isomers (termed as NTU-69 and NTU-70) was prepared from a C_2v symmetric diimidazole–dicarboxylate ligand and mononuclear Cu ion. The structural differences arise from the different rotation configuration of the sp² bond in the ligand, leading them to exhibit completely different topologies of unc (NTU-69) and sod (NTU-70) as well as framework rigidness. This rotation configuration of the sp² bond can be controlled by the different acidity of the synthetic solution and the metal/ligand ratio. Gas adsorption and IAST selectivity show that NTU-70 features high potential for CH₄ purification from C₂H₄, C₂H₆, C₃H₆ and CO₂ mixtures at room temperature. The insight from this work establishes a new bridge between the ligand design and controlled construction of porous isomers.