Defect Engineering of Copper Paddlewheel-Based Metal–Organic Frameworks of Type NOTT-100: Implementing Truncated Linkers and Its Effect on Catalytic Properties

Abstract

A series of new defect-engineered metal−organic frameworks (DEMOFs) were synthesized by framework doping with truncated linkers employing the mixed-linker approach. Two tritopic defective (truncated) linkers, biphenyl-3,3′,5-tricarboxylates (L H ) lacking a ligating group and 5-(5-carboxypyridin-3yl)isophthalates (L Py ) bearing a weaker interacting ligator site, were integrated into the framework of Cu 2 (BPTC) (NOTT-100, BPTC = biphenyl-3,3′,5,5′-tetracarboxylates). Incorporating L H into the framework mainly generates missing metal node defects, thereby obtaining dangling COOH groups in the framework. However, introducing L Py forms more modified metal nodes featuring reduced and more accessible Cu sites. In comparison with the pristine NOTT-100, the defect-engineered NOTT-100 (DE-NOTT-100) samples show two unique features: (i) functional groups (the protonated carboxylate groups as the Brønsted acid sites or the pyridyl N atoms as the Lewis basic sites), which can act as second active sites, are incorporated into the MOF frameworks, and (ii) more modified paddlewheels, which provided extra coordinatively unsaturated sites, are generated. The cooperative functioning of the above characteristics enhances the catalytic performance of certain types of reactions. For a proof of concept, two exemplary reactions, namely, the cycloaddition of CO 2 with propylene oxide to propylene carbonate and the cyclopropanation of styrene, were carried out to evaluate the catalytic activities of those DE-NOTT-100 materials depending on the defect structure.

Synthesis, characterization and application of defective metal–organic frameworks: current status and perspectives

“…The mixedlinker approach can increase the number of defect sites or active sites by incorporating another linker with various unique functionalities. 34,[60][61][62][63] By using this mixed-linker approach, Epp et al 61 successfully introduced point defects at the distinct Ru 2 paddlewheel nodes in ruthenium MOF Ru-HKUST-1. Mixtures of benzene-1,3,5-tricarboxylate and pyridine-3,5-dicarboxylate linkers were used in the mixed-linker approach.…”

The Role of Defects in Metal–Organic Frameworks for Nitrogen Reduction Reaction: When Defects Switch to Features

“…[ 121 ] Recently, many research works have used this strategy to introduce defective MOFs. [ 98,122,123 ] Lee et al. introduced defects into MOFs by designing multicomponent MOFs, [ 122 ] which involve substantial ligands (4,4′,4″‐nitrilotrisbenzoate) for preserving the framework structure along with decorative ligands (dabco and 4,4′‐bipyridyl) by removing these nonessential ligands, the vacancy defects were created easily (Figure 6c).…”

Spatio‐Chemical Heterogeneity of Defect‐Engineered Metal–Organic Framework Crystals Revealed by Full‐Field Tomographic X‐ray Absorption Spectroscopy

“…[8,9] Fore xample,b yc reating coordinatively unsatu-rated framework nodes,the catalytic properties of aMOF can be tuned. [10][11][12][13] An otable difference between defect engineering in MOFs and, for example,o xides is the proclaimed ease and tailoring at which defects can be created. Specific defects can be introduced in adefined quantity through the proportional addition of ap urpose-selected defective linker.…”

“…XANES spectroscopy [26] and the corresponding tomography techniques [27][28][29][30][31][32] are capable of unveiling the chemical state,s tructure and coordination around as elected chemical element, here copper. Thel ocal coordination environment of copper can change around the defect sites compared to "perfect" defectfree MOF crystal sites, [12,13] as well as comparing different types of defect, which can attribute different functionalities to MOFs. [12] Experiments revealed as patially non-uniform incorporation of defective linker,l eading to cluster formation of an anocrystalline secondary coordination polymer rich in defective linker throughout the crystals.T hese clusters possess ar educed metal concentration and coordination number compared to the surrounding HKUST-1 framework.…”

“…Thel ocal coordination environment of copper can change around the defect sites compared to "perfect" defectfree MOF crystal sites, [12,13] as well as comparing different types of defect, which can attribute different functionalities to MOFs. [12] Experiments revealed as patially non-uniform incorporation of defective linker,l eading to cluster formation of an anocrystalline secondary coordination polymer rich in defective linker throughout the crystals.T hese clusters possess ar educed metal concentration and coordination number compared to the surrounding HKUST-1 framework. While the frequency of these clusters is positively correlated with defective linker concentration in the crystallization environment, such clusters can equally be found in HKUST-1 crystals synthesized without defective linker.T his suggests that the formation of the secondary coordination polymer is associated with ap ost-synthesis collapse of the MOF lattice and mesopore formation, the latter two driven by alocally increased density of crystallographic defects,which is possibly enhanced by the zonation and clustering of defective linkers during MOF synthesis.O bservations suggest some of the altered properties of defect-engineered MOFs,f or example,c hanges in porosity and copper coordination, affecting gas sorption and catalytic properties to partially result from these coordination polymer clusters.…”