Postsynthetic Metalation of Bipyridyl-Containing Metal–Organic Frameworks for Highly Efficient Catalytic Organic Transformations

A lead-porphyrin metal-organic framework: gas adsorption properties and electrocatalytic activity for water oxidation

A 3D non-interpenetrating porous metal-organic framework [Pb2(H2TCPP)]·4DMF·H2O (Pb-TCPP) (H6TCPP = 5,10,15,20-tetra(carboxyphenyl)porphyrin) was synthesized by employment of a robust porphyrin ligand. Pb-TCPP exhibits a one-dimensional channel possessing fairly good capability of gas sorption for N2, H2, Ar, and CO2 gases, and also features selectivity for CO2 over CH4 at 298 K. Furthermore, Pb-TCPP shows electrocatalytic activity for water oxidation in alkaline solution. It is the first 3D porous Pb-MOF that exhibits both gas adsorption properties and electrocatalytic activity for an oxygen evolution reaction (OER).

Encapsulation of an organometallic cationic catalyst by direct exchange into an anionic MOF

Metal-Organic Frameworks (MOFs) are porous crystalline materials that have emerged as promising hosts for the heterogenization of homogeneous organometallic catalysts, forming hybrid materials which combine the benefits of both classes of catalysts. Herein, we report the encapsulation of the organometallic cationic Lewis acidic catalyst [CpFe(CO)2(L)]+ ([Fp-L]+, Cp = η5-C5H5, L = weakly bound solvent) inside the pores of the anionic [Et4N]3[In3(BTC)4] MOF (H3BTC = benzenetricarboxylic acid) via a direct one-step cation exchange process. To conclusively validate this methodology, initially [Cp2Co]+ was used as an inert spatial probe to (i) test the stability of the selected host; (ii) monitor the stoichiometry of the cation exchange process and (iii) assess pore dimensions, spatial location of the cationic species and guest-accessible space by single crystal X-ray crystallography. Subsequently, the quasi-isosteric [Fp-L]+ was encapsulated inside the pores via partial cation exchange to form [(Fp-L)0.6(Et4N)2.4][In3(BTC)4]. The latter was rigorously characterized and benchmarked as a heterogeneous catalyst in a simple Diels-Alder reaction, thus verifying the integrity and reactivity of the encapsulated molecular catalyst. These results provide a platform for the development of heterogeneous catalysts with chemically and spatially well-defined catalytic sites by direct exchange of cationic catalysts into anionic MOFs.

Graphene-Immobilized fac-Re(bipy)(CO)3Cl for Syngas Generation from Carbon Dioxide

We report the synthesis of fac-M(4-amino-bipy)(CO)3X (M = Mn and X = Br or M = Re and X = Cl, with bipy = 2,2'-bipyridine), their immobilization on graphene oxide (GrO) via diazonium grafting, and the use of Re-functionalized GrO for electrocatalytic syngas production. Infrared (IR) spectroscopy, X-ray absorption fine structure (XAFS) spectroscopy, and electrocatalysis indicated successful grafting of the Re catalyst onto GrO. Re-functionalized GrO was then deposited onto a glassy carbon electrode (GCE) for CO2 reduction. Investigation of the Re-functionalized GCE for syngas production was performed in a CO2-saturated acetonitrile solution with 3.1 M H2O as the proton source and 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6) as the supporting electrolyte. Cyclic voltammetry (CV), controlled potential electrolysis (CPE), and gas chromatography (GC) were employed to determine its CO2-to-CO conversion performance. The Re catalyst shows a turnover frequency (TOF) for generating CO up to 4.44 s(-1) with a CO/H2 ratio of 7:5.

A Simple and Non-Destructive Method for Assessing the Incorporation of Bipyridine Dicarboxylates as Linkers within Metal-Organic Frameworks

As a novel avenue for applications, metal-organic frameworks (MOFs) are increasingly used for heterogenizing catalytic molecular species as linkers into their crystalline framework. These multifunctional compounds can be accessed with mixed linkers synthesis or postsynthetic-exchange strategies. Major limitations still reside in their challenging characterization; in particular, to provide evidence of the genuine incorporation of the functionalized linkers into the framework and their quantification. Herein, we demonstrate that a combination of computational chemistry, spectroscopy and X-ray diffraction allows access to a non-destructive analysis of mixed-linker UiO-67-type materials featuring biphenyl- and bipyridine-dicarboxylates. Our UV/Vis-based methodology has been further applied to characterize a series of Rh-functionalized UiO-67-type catalysts. The proposed approach allows a recurrent key issue in the characterization of similar supported organometallic systems to be solved.

Construction of Four Zn(II) Coordination Polymers Used as Catalysts for the Photodegradation of Organic Dyes in Water

Hydrothermal reactions of Zn(OAc)₂·2H₂O with flexible bipyridyl benzene ligand and three dicarboxylic derivatives gave rise to four new coordination polymers, [Zn₇(μ₄-O)₂(OAc)₁₀(bpmb)]_n (1), [Zn(5-OH-1,3-BDC)(bpmb)]_n (2), [Zn(1,2-BDC)(bpmb)]_n (3) and [Zn₂(ADB)₂(bpmb)]_n (4) (bpmb = 1,4-bis(pyridine-3-ylmethoxy)benzene, 5-OH-1,3-H₂BDC = 5-hydroxy-1,3-benzenedicarboxylic acid, 1,2-H₂BDC = 1,2-benzenedicarboxylic acid, H₂ADB = 2,2’-azodibenzoic acid). Their structures were characterized by single-crystal X-ray diffraction, elemental analyses, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Compound 1 features a one-dimensional (1D) chain structure based on the rare heptanuclear [Zn₇(μ₄-O)(μ₃-OAc)₂(μ₂-OAc)₈] units. Compound 2 exhibits a novel 2D bilayer structure built from the two parallel 2D (4,4) layers. Compound 3 holds a 2D structure in which the 1,2-BDC ligands work as lockers interlocking 1D [Zn(bpmb)]_n chain. Compound 4 comprises a 3D framework constructed by 2D wrinkled [Zn₂(ADB)₄]_n networks and bpmb linkers with a six-connected pcu net. These results suggest that the motifs of the dicarboxylic ligands have significant effect on the final structures. These compounds exhibited relatively good photocatalytic activity towards the degradation of methylene blue (MB) in aqueous solution under a Xe lamp irradiation.

Tuning the properties of the metal–organic framework UiO-67-bpy via post-synthetic N-quaternization of pyridine sites

N-Quaternization of pyridine sites in UiO-67-bpy affords a cationic MOF UiO-67-bpy-Me with faster and improved anionic dye and CO₂adsorption, and extended visible-light absorption properties, which make UiO-67-bpy-Me more efficient in photodegrading organic dyes.

Bipyridyl palladium embedded porous organic polymer as highly efficient and reusable heterogeneous catalyst for Suzuki–Miyaura coupling reaction

Bipyridyl-palladium catalyst embedded porous organic polymers (Bpy-Pd-POP) was synthesized and used as highly effective and reusable heterogeneous catalyst for the Suzuki–Miyaura coupling reaction.

MOF-253-Pd(OAc)2: a recyclable MOF for transition-metal catalysis in water

We report palladium(ii)-functionalized MOF-253 (MOF-253-Pd(OAc)₂) as a recyclable catalyst to form all-carbon quaternary centers via conjugate additions of arylboronic acids to β,β-disubstituted enones in aqueous media.

Zr-based metal–organic frameworks: design, synthesis, structure, and applications

This review summarizes the advances in the study of Zr-based metal–organic frameworks in terms of their design, synthesis, structure, and potential applications.

A visible-light responsive zirconium metal–organic framework for living photopolymerization of methacrylates

Visible-light-induced living radical polymerization of methacrylates by using robust zirconium metal–organic frameworks.

One-Step Synthesis of Nanoscale Zeolitic Imidazolate Frameworks with High Curcumin Loading for Treatment of Cervical Cancer

A straightforward nanoprecipitating method was developed to prepare water dispersible curcumin (CCM)-loaded nanoscale zeolitic imidazolate framework-8 (CCM@NZIF-8) nanoparticles (NPs). The as-synthesized CCM@NZIF-8 NPs possess high drug encapsulation efficiency (88.2%), good chemical stability and fast drug release in tumor acidic microenvironments. Confocal laser scanning microscopy and cytotoxicity experiments reveal that NZIF-8 based nanocarriers promote the cellular uptake of CCM and result in higher cytotoxicity of CCM@NZIF-8 than that of free CCM toward HeLa cells. The in vivo anticancer experiments indicate that CCM@NZIF-8 NPs exhibit much higher antitumor efficacy than free CCM. This work highlights the potential of using nanoscale metal organic framworks (NMOFs) as a simple and stable platform for developing a highly efficient drug delivery system in cancer treatment.

Seed-mediated growth of MOF-encapsulated Pd@Ag core-shell nanoparticles: toward advanced room temperature nanocatalysts

Core–shell Pd@Ag nanoparticles are formed within the pores of MOFs via a seed mediated growth strategy with activated hydrogen atoms as the reducing agent, leading to a family of bimetallic core–shell MOF nanomaterials with excelling catalytic performance in room temperature reactions.

The possibility of using inner cavities within metal–organic frameworks (MOFs) as templates for the fabrication of tiny metal nanoparticles (NPs) was attempted in this work. An unprecedented design of Pd@Ag core–shell NPs on MOFs via a seed mediated growth strategy is reported and attributed to the presence of activated physisorbed hydrogen atoms on embedded Pd NPs as reducing agents to selectively direct the deposition of Ag onto Pd while minimizing the Ag self-nucleation. The obtained Pd@Ag core–shell NPs exhibited a significant increase in selectivity in the partial hydrogenation of phenylacetylene as compared to their monometallic counterparts, due to the surface dilution and electron modification of the surface Pd sites by Ag deposition. Pd@Ag NPs also possessed an unprecedented high stability and recyclability in the catalytic reactions, related to the nano-confinement effect and the strong metal–support interaction offered by the MOF framework.

The first chiral diene-based metal-organic frameworks for highly enantioselective carbon-carbon bond formation reactions

The first chiral rhodium-diene-based metal–organic frameworks are highly active and enantioselective catalysts for C–C bond formation reactions.

We have designed the first chiral diene-based metal–organic framework (MOF), E₂-MOF, and postsynthetically metalated E₂-MOF with Rh(i) complexes to afford highly active and enantioselective single-site solid catalysts for C–C bond formation reactions. Treatment of E₂-MOF with [RhCl(C₂H₄)₂]₂ led to a highly enantioselective catalyst for 1,4-additions of arylboronic acids to α,β-unsaturated ketones, whereas treatment of E₂-MOF with Rh(acac)(C₂H₄)₂ afforded a highly efficient catalyst for the asymmetric 1,2-additions of arylboronic acids to aldimines. Interestingly, E₂-MOF·Rh(acac) showed higher activity and enantioselectivity than the homogeneous control catalyst, likely due to the formation of a true single-site catalyst in the MOF. E₂-MOF·Rh(acac) was also successfully recycled and reused at least seven times without loss of yield and enantioselectivity.

Concentration Dependent Dimensionality of Resonance Energy Transfer in a Postsynthetically Doped Morphologically Homologous Analogue of UiO-67 MOF with a Ruthenium(II) Polypyridyl Complex

A method is described here by which to dope ruthenium(II) bis(2,2'-bipyridine) (2,2'-bipyridyl-5,5'-dicarboxylic acid), RuDCBPY, into a UiO-67 metal-organic framework (MOF) derivative in which 2,2'-bipyridyl-5,5'-dicarboxylic acid, UiO-67-DCBPY, is used in place of 4,4'-biphenyldicarboxylic acid. Emission lifetime measurements of the RuDCBPY triplet metal-to-ligand charge transfer, (3)MLCT, excited state as a function of RuDCBPY doping concentration in UiO-67-DCBPY are discussed in light of previous results for RuDCBPY-UiO-67 doped powders in which quenching of the (3)MLCT was said to be due to dipole-dipole homogeneous resonance energy transfer, RET. The bulk distribution of RuDCBPY centers within MOF crystallites are also estimated with the use of confocal fluorescence microscopy. In the present case, it is assumed that the rate of RET between RuDCBPY centers has an r(-6) separation distance dependence characteristic of Förster RET. The results suggest (1) the dimensionality in which RET occurs is dependent on the RuDCBPY concentration ranging from one-dimensional at very low concentrations up to three-dimensional at high concentration, (2) the occupancy of RuDCBPY within UiO-67-DCBPY is not uniform throughout the crystallites such that RuDCBPY densely populates the outer layers of the MOF at low concentrations, and (3) the average separation distance between RuDCBPY centers is ∼21 Å.

Probing post-synthetic metallation in metal-organic frameworks: insights from X-ray crystallography

For post-synthetic metallation (PSMet) of a metal–organic framework (MOF, [Mn3(L2)(L')] = 1) we show a solvent dependency for the form of the metallated product. PSMet of 1 with MnCl2 in ethanol leads to a single metal entity per coordinating site while acetonitrile yields a remarkably complex multiply metallated product; thus, determining the extent of metallation requires an intimate understanding of the chemistry occurring in the MOF pores.

Encapsulation of Mono- or Bimetal Nanoparticles Inside Metal-Organic Frameworks via In situ Incorporation of Metal Precursors

A facile, in situ metal precursor incorporation strategy is established for good control over the location and composition of metal nanoparticles within metal-organic frameworks (MOFs). This one-step metal precursor incorporation route is successfully applied to the fabrication of ultrafine Pd, Ni, and PdNi alloys to be selectively encapsulated inside the pores of MOFs, achieving superior catalytic activity and stability in the hydrogenation of nitrobenzene.

Stable porphyrin Zr and Hf metal-organic frameworks featuring 2.5 nm cages: high surface areas, SCSC transformations and catalyses

Two isostructural porphyrin Zr and Hf metal-organic frameworks (FJI-H6 and FJI-H7) are rationally synthesized, and are constructed from 2.5 nm cubic cages. Notably, they both possess high water and chemical stability and can undergo single-crystal to single-crystal transformations to embed Cu2+ ions into the open porphyrin rings. FJI-H6 has a high BET surface area of 5033 m2 g-1. Additionally, they exhibit promising catalytic abilities to convert CO2 and epoxides into cyclic carbonates at ambient conditions.

Single-crystal-to-single-crystal metalation of a metal-organic framework: a route toward structurally well-defined catalysts

Metal-organic frameworks featuring ligands with open chelating groups are versatile platforms for the preparation of a diverse set of heterogeneous catalysts through postsynthetic metalation. The crystalline nature of these materials allows them to be characterized via X-ray diffraction, which provides valuable insight into the structure of the metal sites that facilitate catalysis. A highly porous and thermally robust zirconium-based metal-organic framework, Zr6O4(OH)4(bpydc)6 (bpydc(2-) = 2,2'-bipyridne-5,5'-dicarboxylate), bears open bipyridine sites that readily react with a variety of solution- and gas-phase metal sources to form the corresponding metalated frameworks. Remarkably, Zr6O4(OH)4(bpydc)6 undergoes a single-crystal-to-single-crystal transformation upon metalation that involves a change in space group from Fm3̅m to Pa3̅. This structural transformation leads to an ordering of the metalated linkers within the framework, allowing structural characterization of the resulting metal complexes. Furthermore, Zr6O4(OH)4(bpydc)6 yields an active heterogeneous catalyst for arene C-H borylation when metalated with [Ir(COD)2]BF4 (COD = 1,5-cyclooctadiene). These results highlight the unique potential of metal-organic frameworks as a class of heterogeneous catalysts that allow unparalleled structural characterization and control over their active sites.

Eu(III)-functionalized MIL-124 as fluorescent probe for highly selectively sensing ions and organic small molecules especially for Fe(III) and Fe(II)

A layerlike MOF (MIL-124, orGa2(OH)4(C9O6H4)) has been prepared and chosen as a parent compound to encapsulate Eu(3+) cations by one uncoordinated carbonyl group in its pores. The Eu(3+)-incorporated sample (Eu(3+)@MIL-124) is fully characterized, which shows excellent luminescence and good fluorescence stability in water or other organic solvents. Subsequently, we choose Eu(3+)@MIL-124 as sensitive probe for sensing metal ions, anions, and organic small molecules because of its robust framework. Studying of the luminescence properties reveals that the complex Eu(3+)@MIL-124 was developed as a highly selective and sensitive probe for detection of Fe(3+) (detection limit, 0.28 μM) and Fe(2+) ions through fluorescence quenching of Eu(3+) and MOF over other metal ions. In connection to this, a probable sensing mechanism was also discussed in this paper. In addition, when Eu(3+)@MIL-124 was immersed in the different anions solutions and organic solvents, it also shows highly selective for Cr2O7(2-)(detection limit, 0.15 μM)and acetone. Remarkably, it is the first Eu-doped MOF to exhibit an excellent ability for the detection of Fe(3+) and Fe(2+) in an aqueous environment without any structural disintegration of the framework.

Turning on catalysis: incorporation of a hydrogen-bond-donating squaramide moiety into a Zr metal-organic framework

Herein, we demonstrate that the incorporation of an acidic hydrogen-bond-donating squaramide moiety into a porous UiO-67 metal-organic framework (MOF) derivative leads to dramatic acceleration of the biorelevant Friedel-Crafts reaction between indole and β-nitrostyrene. In comparison, it is shown that free squaramide derivatives, not incorporated into MOF architectures, have no catalytic activity. Additionally, using the UiO-67 template, we were able to perform a direct comparison of catalytic activity with that of the less acidic urea-based analogue. This is the first demonstration of the functionalization of a heterogeneous framework with an acidic squaramide derivative.

Intercalation of lanthanide cations to a layer-like metal–organic framework for color tunable white light emission

MIL-124 has been synthesized by solvothermal approach, and the luminescence was tuned by doping Ln³⁺ into the channels. With adjustment of the excitation wavelength and concentration of Ln³⁺, dichromatic (MIL-124@Eu³⁺) and trichromatic (MIL-124@Eu³⁺/Tb³⁺) white-light-emission can be achieved.

Luminescent zinc metal–organic framework (ZIF-90) for sensing metal ions, anions and small molecules

We synthesize ZIF-90, which exhibits an intense blue luminescence excited under visible light. Luminescent studies indicate that ZIF-90 could be an efficient multifunctional fluorescence material for sensing metal cations, anions and organic small molecules.

Assembly of three coordination polymers based on a sulfonic–carboxylic ligand showing high proton conductivity

Three MOFs with different structures all exhibit proton conduction behavior, especially for the Cu compound with a proton conductivity of 3.46 × 10⁻³ S cm⁻¹ at 368 K and 95% RH.