Generation of Defect‐Modulated Metal–Organic Frameworks by Fragmented‐Linker Co‐Assembly of CPO‐27(M) Frameworks

Abstract

The generation of defect‐modulated metal–organic frameworks (MOFs) by the successful stepwise doping of 2‐hydroxyterephthalate (BDC‐OH) into frameworks of the CPO‐27‐M type is discussed. The influence of MgII, CoII, and NiII ions on the product formation has been investigated by powder XRD (PXRD), IR spectroscopy, and thermal analysis. To establish the successful incorporation of the fragmented linker molecule, 1H NMR spectra were recorded after the digestion of the MOFs in DCl/[D6]dimethyl sulfoxide. After the incorporation of BDC‐OH, microporous structures were generated with reasonable porosity. The morphologies of the reaction products were checked by SEM measurements, and no significant changes to the morphologies were observed after the fragmented‐linker doping.

Increasing Exposed Metal Site Accessibility in a Co-MOF-74 Material With Induced Structure-Defects

“…The TG curves show two main weight losses that correspond to solvent removal between 50 and 150 • C, and linker combustion above 280 • C. The latter leads to formation of the metal oxide. These temperatures are in accordance with those previously reported for methanolwashed MOF-74 materials (El-Gamel, 2015). The temperature for maximum mass loss rate (minimum of dTG-curves) in the solvent loss is higher than the boiling point of methanol due to strong interactions of solvent with the EMS, as commented above, but also some kinetic effects like diffusion could be involved.…”

“…Therefore, the reduction of crystallinity after drying in vacuum indicates a reduction in the stability of the crystal phase of the material after the partial substitution of its linker. The importance of solvent molecules for maintaining the structural stability of the modified MOF-74 structures can be a direct consequence of the presence of structural defects, that were also assumed in similar works (El-Gamel, 2015;Wu et al, 2017). Figure 1 depicts how defects are supposed to be created, as a consequence of the mixture of linkers with different topology.…”

“…The only exception was for syntheses involving more than 90% of dhbz in the initial solution, for which no solid product was obtained. This could be due to the incorporation of hbdc and the lack of dhbz in mixedlinker M-MOF-74 materials (M: Mg, Co, Ni, or Mn) that was reported in previous works (El-Gamel, 2015;Wu et al, 2017). A possible explanation for this fact is that hydroxybenzoic acid is a monocarboxylic acid, so this substance could just chelate single metal cations avoiding polymerization.…”

“…The creation of structural defects has also been studied in MOF-74 structures by mixing the original linker with some terephthalic or benzoic acid derivatives. These derivative linkers exhibit different topologies and are proposed to reduce the coordination degree of metal atoms in the structure (El-Gamel, 2015;Wu et al, 2017). In these works, MOF-74-like structures with induced structural defects were synthesized by using Co, Ni, Mg, or Mn as metals, and their structural properties and CO 2 adsorption behavior were investigated.…”

“…Here, we investigate the creation of structural defects in a Co-MOF-74 structure by partially mixing the linker dhbdc with two modifications of this linker: 2,5-dihydroxybenzoic acid (dhbz) and hydroxyterephthalic acid (hbdc), as shown in Figure 1. The linker dhbz was used as a reference since this does not incorporate in the MOF-74 structure (El-Gamel, 2015;Wu et al, 2017). The structural properties of the synthesized materials were compared by powder X-ray diffraction, after different drying-treatments.…”