Intramolecular hydrogen bond-induced high chemical stability of metal–organic frameworks

Abstract

Insufficient chemical stability of numerous metal–organic frameworks (MOFs) restricts their widespread use. Achieving high thermodynamic stability is not a universal method to obtain chemically stable MOFs because kinetic stability also has a significant effect. Here, in contrast to a hydrogen bond between two adjacent ligands in MOFs needing rational framework structures, an intramolecular hydrogen bond in ligands was engineered to enhance the chemical stability of MOFs. As a proof-of-concept demonstration, 3,3′-diamino-1,1′-biphenyl-4,4′-dicarboxylic acid (H₂BPDC-o-(NH₂)₂) with the intramolecular hydrogen bonds and 2,2′-diamino-1,1′-biphenyl-4,4′-dicarboxylic acid (H₂BPDC-m-(NH₂)₂) without the intramolecular hydrogen bonds were synthesized to construct UiO-67-o-(NH₂)₂ and UiO-67-m-(NH₂)₂, respectively. Intramolecular hydrogen bonds were found to increase the torsional rigidity of carboxyl groups relative to the adjacent aromatic rings in ligands and to favour the repair of broken coordination bonds of MOFs. Consequently, UiO-67-o-(NH₂)₂ is more chemically stable than UiO-67-m-(NH₂)₂ in H₂O, pH = 2 HCl solution, and pH = 12 NaOH solution. This work not only provides an insight into the contribution of intramolecular hydrogen bonds in ligands to the stability of MOFs but provides a strategy to design highly stable MOFs for widespread use.