Inorganic functionalization of metal–organic frameworks (MOFs), such as incorporation of multiple inorganic building blocks with distinct metals into one structure and further modulation of the metal charges, endows the porous materials with significant properties toward their applications in catalysis. In this work, by an exploration of the role of 4-pyrazolecarboxylic acid (H2PyC) in the formation of trinuclear copper pyrazolate as a metalloligand in situ, four new MOFs with multiple components in order were constructed through one-pot synthesis. This metalloligand strategy provides multicomponent MOFs with new topologies (tub for FDM-4 and tap for FDM-5) and is also compatible with a second organic linker for cooperative construction of complex MOFs (1,4-benzenedicarboxylic acid for FDM-6 and 2,6-naphthalenedicarboxylic acid for FDM-7). The component multiplicity of these MOFs originates from PyC’s ability to separate Cu and Zn on the basis of their differentiated binding affinities toward pyrazolate and carboxylate. These MOFs feature reversible and facile redox transformations between CuI3(PyC)3 and CuII3(μ-OH)(PyC)3(OH)3 without altering the connecting geometries of the units, thus further contributing to the significant catalytic activities in the oxidation of CO and aromatic alcohols and the decomposition of H2O2. This study on programming multiple inorganic components into one framework and modulating their electronic structures is an example of functionalizing the inorganic units of MOFs with a high degree of control.

•Defects in two Mn-based MOFs were investigated by employing fragmented linkers.•The defect density was impacted by the coordinating groups in the fragmented linker.•Surface area enhancement was observed in the defected MOF structure.Formation of defects with controlled concentration in Mn-MOF-74 [Mn2(DOBDC), DOBDC: 2,5-dioxido-1,4-benzenedicarboxylic acid] and a newly synthesized metal–organic framework Mn5(BDC-O)2(BDC-OH)2 (FDM-21, BDC-OH: 2-hydroxyterephthalic acid) were systematically investigated by employing fragmented linkers with reduced coordination numbers towards Mn(II) during the synthesis. The defect engineering has resulted in missing functional groups on the framework backbone, as well as potential open metal sites in the inorganic secondary building units. The chemical form and amount of coordinating groups (–OH and/or –COOH) in the fragmented linkers have impacted the defects density of the framework significantly. Furthermore, surface area enhancement was observed in the defected Mn-MOF-74 doped with BDC-OH, compared to the defect-free Mn-MOF-74.Defects with controlled concentrations in Mn-based MOFs with rod-shaped inorganic building units were systematically investigated by employing fragmented linkers with reduced coordination numbers. The chemical form and amount of coordinating groups (–OH and/or –COOH) in each linker impact on the defects density and porosity of the framework significantly.Download high-res image (104KB)Download full-size image

A hydrogen-bonded organic framework (HOF) was constructed by avoiding potential π–π stacking of building blocks with robust and non-coplanar triptycene-based modules. The tailored-fitting interactions were demonstrated by the adsorption of fullerene with a concentration enrichment of ∼420 times in the pores.

Rechargeable nonaqueous Li–O2 batteries have been considered as one of the most promising candidate energy storage devices. In this work, metal–organic framework nanomaterials with distinct sizes and morphologies were successfully synthesized via a facile solvothermal method. By using modulators in a mixed solvent system, the dimension of Co-MOF-74 could be reduced down to several unit cell lengths. Furthermore, high specific capacities (11 350 mA h g−1 at 100 mA g−1) were achieved when they were directly employed as cathode materials for Li–O2 batteries. In addition to the high density of unsaturated active sites for electrochemistry, as provided by the MOF skeleton itself, the size confinement and inherent defects of the nanocrystals have further offered efficient diffusion paths with lowered transport barriers, contributing to their high performance in Li–O2 batteries.

In situ fabrication of graphene scaffold–ZrO2 nanofilms is achieved by thermal annealing of Zr-based metal–organic oligomers on SiO2 substrates. The structural similarities of the aromatic moieties in the ligand (phenyl-, naphthyl-, anthryl-, and pyrenyl-) compared to graphene play a major role in the ordering of the graphene scaffolds obtained. The depth profiling analysis reveals ultrathin carbon-pure or carbon-rich surfaces of the graphene scaffold–ZrO2 nanofilms. The graphene scaffolds with ∼96.0% transmittance in the visible region and 4.8 nm in thickness can be grown with this non-chemical vapor deposition method. Furthermore, the heterogeneous graphene scaffold–ZrO2 nanofilms show a low sheet resistance of 17.0 kΩ per square, corresponding to electrical conductivity of 3197 S m–1. The strategy provides a facile method to fabricate graphene scaffolds directly on high-k dielectrics without transferring process, paving the way for its application in fabricating electronic devices.Keywords: electronic materials; graphene scaffold; high-k dielectrics; metal−organic oligomer; transfer-free

Incorporating supramolecular interaction units, crown ether rings, into metal–organic frameworks enables the docking of metal ions through complexation for enhanced performance in H2 and CO2 adsorption and lithium ion batteries.

Materials built from multiple constituents have revealed emerging properties that are beyond linear integration of those from single components. We report a mesoporous metal–organic framework made from three geometrically distinct metal-containing secondary building units (SBUs) as a result of topological induction. The combinations of the Cu-based triangular, Zn-based octahedral, and Zn-based square pyramidal SBUs have created four types of cages in the network, despite that only one organic linker pyrazolecarboxylate was used. The longest distance for molecules maneuvering inside the largest cage is 5.2 nm. Furthermore, the complex and diversified pore environments allow the installation of various new functionalities in the framework as well as the expedited Ag nanoparticle formation in the pores. As presented in the molecule movement diagram, the crystal has provided specific arrangements of cages and apertures with distinct chemical features for guests transporting between the pores.

When the supramolecular building block packings (face-centered, body-centered, and primitive cubic) with different interactions (hydrogen and coordination bonding) were controlled, four new structures based on octahedral MII (M = Zn, Ni, Mn) and imidazoledicarboxylate were constructed. The interaction modes between the supramolecular building blocks affect the water stability of the structures. Furthermore, with uncoordinated carboxylate O atoms in the structures, these compounds demonstrate a strong capability of capturing metal ions in the solution.

Vacancies are common in solid materials, but it remains a challenge to introduce them at specific locations with controlled distributions. Here we report the creation of ordered metal vacancies and linker vacancies in a cubic metal–organic framework (MOF) based on Zn(II) and pyrazolecarboxylic acid by removing a quarter of the metal ions and half of the linkers. The MOF with ordered vacancies shows increased pore size, thus allowing large dye molecules to fit in the pores. Furthermore, by filling the vacancies with new metals and new linkers, eight new single-crystalline MOFs with multicomponents in absolute order are introduced. The capability of performing stepwise elimination and addition reactions systematically in extended solids without destroying the structural integrity has generated complex MOF structures which otherwise cannot be made.

Two types of rod-shaped building units are arranged periodically with adenine unprecedentedly to generate a metal–organic framework with hexagonal one-dimensional channels. The new planar double-metal string building blocks in this MOF were obtained by controlling the coordination variation of adenine molecules.

Metal-organic frameworks (MOFs) constructed from conjugated organic ligands are candidates for hybrid photoactive materials with potential applications. Compared to that from the ligands only, the intensity and wavelength of the luminescence could be tuned after they were incorporated in extended framework. In this report, by using an organic ligand with azolate moiety, benzo-bis(imidazole) (H2BBI), we synthesized two new MOF structures. Framework 1 ([Co(H2BBI)(DMSO)2Cl2]n, DMSO = dimethyl sulfoxide), constructed from tetrahedral Co(II) and H2BBI, exhibits zigzag 1D structure. Meanwhile, framework 2 ([Cu2(H2BBI)3(DMSO)6(NO3)4]n), a layered structure with hcb topology, was assembled from tetragonal pyramidal Cu(II) and H2BBI. Furthermore, 2 exhibits strong luminescence emission (λex = 280 nm). A blue shift of 40 nm (from 359 nm to 319 nm) was observed in framework 2 compared to the free ligand, which could be explained by the ligand-to-metal charge transfer in the network.

Organic links of varied structure metrics and functionalities connect with Cu2(COO)4 clusters to afford layered metal–organic frameworks. Through topological and pore control, polyoxometalates could be synthetically encapsulated within the cavities. The templating effects of polyoxometalates and specific link functionalizations provide two strategies for controllably incorporating these active species into frameworks.

A hydrogen-bonded organic framework (HOF) was constructed by avoiding potential π–π stacking of building blocks with robust and non-coplanar triptycene-based modules. The tailored-fitting interactions were demonstrated by the adsorption of fullerene with a concentration enrichment of ∼420 times in the pores.

Rechargeable nonaqueous Li–O2 batteries have been considered as one of the most promising candidate energy storage devices. In this work, metal–organic framework nanomaterials with distinct sizes and morphologies were successfully synthesized via a facile solvothermal method. By using modulators in a mixed solvent system, the dimension of Co-MOF-74 could be reduced down to several unit cell lengths. Furthermore, high specific capacities (11350 mA h g−1 at 100 mA g−1) were achieved when they were directly employed as cathode materials for Li–O2 batteries. In addition to the high density of unsaturated active sites for electrochemistry, as provided by the MOF skeleton itself, the size confinement and inherent defects of the nanocrystals have further offered efficient diffusion paths with lowered transport barriers, contributing to their high performance in Li–O2 batteries.

Incorporating supramolecular interaction units, crown ether rings, into metal–organic frameworks enables the docking of metal ions through complexation for enhanced performance in H2 and CO2 adsorption and lithium ion batteries.