Abstract
Three chelating-amino-functionalized lanthanide metal-organic frameworks, Y-DDQ, Dy-DDQ and Eu-DDQ, were synthesized with a flexible dicarboxylate ligand based on quinoxaline (H2DDQ = N, N′-dibenzoic acid-2,3-diaminoquinoxaline). The three-dimensional framework is constructed by the H2DDQ linkers connecting the zigzag ladders, showing a net of sra topology. In the structures, one kind of Ln(III) ions metal centers are six-coordinated and thus can potentially behave as open metal sites (OMSs), while the free chelating amino groups can act as free functional organic sites (FOSs). The N2 and Ar adsorption behaviors indicate that these Ln-DDQ exhibits stable microporous frameworks with high surface area after remove of the solvents. Owing to presence of OMSs and FOSs, these MOFs show good ability of CO2, dyes captures and Lewis acid catalyst for cyanosilylation reaction. In view of the existing FOSs in the framework, Pd NPs were immobilized onto the MOFs through graft interactions between free chelating amino groups and metal ions precursor using postsynthetic modification. The well dispersed Pd@Ln-DDQs exhibit efficient and recyclable catalytic reduction of 4-nitrophenol to 4-aminophenol, and they can also act as an excellent catalyst for Suzuki-Miyaura cross-coupling reactions with the exposed Pd NPs.
Highlights
Contaminant degradations[20,21]
The disadvantage of most MOFs reported containing functional organic sites are with the monodentate mode, which cannot act as strong supports for the metalation of metal nanoparticle[22]
All the MOFs are isostructural, the structures and properties of Y-DDQ are described in detail here as a representative example
Summary
Contaminant degradations[20,21]. The disadvantage of most MOFs reported containing functional organic sites are with the monodentate mode, which cannot act as strong supports for the metalation of metal nanoparticle[22]. We have designed a flexible dicarboxylicacid ligand containing a functional amino-quinoxaline which possessing a chelating amino site (H2DDQ = N,N′-dibenzoicacid-2,3-diamino-quinoxaline)[23]. Two MOFs with H2DDQ have been synthesized previously with this ligand with the chelating amino sites connected to Zn(II) and Cu(II) ions unluckily[23]. About 17.3 wt % (273 K) and 12.4 wt % (298 K) CO2 can be absorbed at and 760 Torr which suggest that the chelating amino groups and six-coordinated Ln ions have the cooperative interaction with the CO2 molecules. After immobilizing Pd NPs on MOFs through graft interactions from free chelating amino groups using postsynthetic approach, the well dispersed Pd@Ln-MOF exhibited efficient and recyclable catalytic reduction of 4-nitrophenol to 4-aminophenol. Pd@Ln-MOF acts as an efficient catalyst for Suzuki-Miyaura cross-coupling reactions with exposed Pd NPs
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