•For both reactions, CPO-27-Mn is much more active than Mg, Co, Ni and Zn analogs.•Heterogenerity and recyclability of CPO-27-Mn are demonstrated for both reactions.•Cyanosilylation over CPO-27-Mn is ...size selective, typical of porous catalysts.•For styrene oxidation with TBHP, all products are formed via radical mechanisms.
A series of isostructural 3D metal–organic frameworks of 2,5-dihydroxyterephthalate with different metal ions, CPO-27-M (or MOF-74-M, M=Co, Mg, Mn, Ni and Zn), have been studied as catalysts for cyanosilylation of aldehydes with trimethylsilylcyanide and oxidation of styrene with tert-butylhydroperoxide, and two mixed-metal Co-Mn MOFs also studied for cyanosilylation. All these MOFs are active in promoting cyanosilylation, but for styrene oxidation, only the Co and Mn MOFs are active while the others behave as initiators rather than catalysts. For both reactions, CPO-27-Mn exhibits the highest activity, and the catalytic processes are heterogeneous. Radical mechanisms were proposed for the styrene oxidation over CPO-27-Mn, which yields styrene oxide, benzaldehyde and a minor amount of phenylacetaldehyde. The cyanosilylation over CPO-27-Mn shows size selectivity towards aldehyde substrates, and the catalyst can be recycled without losing its structural integrity and catalytic activity. It is also recyclable for styrene oxidation, though the structure changes after the catalytic reaction.
•Mixed azide and carboxylate bridges have led to various nD motifs (n = 0–3).•The simultaneous bridges are ferromagnetic coupler for M(II) (M = Fe, Co, Ni and Cu).•The simultaneous bridges induce ...antiferromagnetic coupling between MnII ions.•The coordination polymers exhibit diverse magnetic ordering behaviors.•Zwitterionic carboxylates led to single-chain magnets and multifunctional materials.
Azide and carboxylate are popular and versatile bridging ligands and magnetic couplers intensively used in the fields of coordination chemistry and molecular magnetism. Combining them in one compound is an interesting approach to construct new magnetic systems. In this review we focus on the structural and magnetic aspects of the coordination polymers containing azide and carboxylate as simultaneous bridges between paramagnetic metal ions. The simultaneous bridges, sometimes in collaboration with other short bridges of different types, have led to discrete, one-, two, and even three-dimensional magnetic motifs. Different from the azide- or carboxylate-only bridges, the simultaneous bridges seem to be universal antiferromagnetic couplers in Mn(II) compounds but tend to induce ferromagnetic exchange in Fe(II), Co(II), Ni(II) and Cu(II) compounds. The coordination polymers show diverse magnetic behaviors, including topological ferrimagnetism, canted antiferromagnetism, metamagnetism, long-range ordering and slow magnetic dynamics. The use of zwitterionic carboxylate ligands have been particularly fruitful in producing mixed-bridge chains, including some Co(II) and Fe(II) ferromagnetic chains behaving as single-chain magnets (SCMs). The antagonistic and synergetic effects of random metal blending on SCM behaviors are commented on. Responsive materials that undergo reversible magnetic changes in response to photoirradiation or water release/uptake are also illustrated.
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•Development of MOF-derived electrodes for electrochemical sensors of neurotransmitters is reviewed.•MOFs act complementarily or synergistically with various materials.•Particular ...attention is paid to the structure-performance relationship.•The current challenges and perspectives in this area are discussed.
Neurotransmitters (NTs) control many behavioral and physiological functions in central and peripheral nervous system, and their detection is of great importance to disease diagnosis and environmental monitoring. Electrochemical sensors have been popular and convenient methods for detection of NTs that are electroactive or can be coupled with electroactive reactions. Metal–organic frameworks (MOFs), constructed by organic ligands connecting metal-based nodes, are promising candidates for electrochemical sensors due to their large surface areas, hybrid structures, tailorable functional sites, and variable catalytic activity. This article gives an overview of the general aspects of MOFs for electrochemical assays of NTs and focused on the state-of-art of the sensors based on MOFs and the composites of MOFs with various materials (mainly carbon-based materials, organic polymers and metal or metal oxide nanoparticle). The use of MOF-derived materials as electrode modifiers is also included.
Metal–organic frameworks (MOFs) provide intriguing platforms for the design of responsive materials. It is challenging to mobilize as many components as possible of a MOF to collaboratively ...accomplish multiple responsive properties. Here, reversible photochromism, piezochromism, hydrochromism, ionochromism, and luminescence modulation of an ionic Eu(III) MOF is reported furnished by cationic electron‐deficient viologen units and exchangeable guest anions. Mechanistically, the extraordinarily versatile responsive properties are owed to electron transfer (ET), charge transfer (CT), and energy transfer, involving viologen as electron acceptor, anion as electron donor, luminescing Eu(III) as energy donor, and anion‐viologen CT complex or ET‐generated radical as energy acceptor (luminescence quencher). Moreover, guest anions and waters provide flexible handles to control the ET‐based responsive properties. Water release/reuptake or exchange with organic solvents can switch on/off the response to light, while reversible anion exchange can disenable or awaken the responses to pressure, light, and water release/reuptake. The impacts of water and anions on ET are justified by the high polarity and hydrogen‐bonding capability of water, the different electron donor strength of anions, and the strong I−‐viologen CT interactions. The rich responsive behaviors have great implications for applications such as pressure sensors, iodide detection, and chemical logic gates.
All components (metal, ligand, guest anion, and solvent) of the ionic metal–organic framework are mobilized to participate in stimuli‐induced electron transfer, charge transfer, or energy transfer, resulting in reversible piezochromism, hydrochromism, photochromism, ionochromism, and concomitant luminescence quenching. The responsive properties can be switched on/off through anion and solvent exchange.
Positive cooperative binding, a phenomenon prevalent in biological processes, holds great appeal for the design of highly sensitive responsive molecules and materials. It has been demonstrated that ...metal–organic frameworks (MOFs) can show positive cooperative adsorption to the benefit of gas separation, but potential binding cooperativity is largely ignored in the study of sensory MOFs. Here, we report the first demonstration of positive cooperative protonation of a MOF and the relevant pH response in fluorescence and proton conduction. The MOF is built of Zr–O clusters and bipyridyl-based tetracarboxylate linkers and has excellent hydrolytic stability. It shows a unique pH response that features two synchronous abrupt turn-off and turn-on fluorescent transitions. The abrupt transitions, which afford high sensitivity to small pH fluctuations, are due to cooperative protonation of the pyridyl sites with a Hill coefficient of 1.6. The synchronous dual-emission response, which leads to visual color change, is ascribable to proton-triggered switching between (n, π*) and (π, π*) emissions. The latter emission can be quenched by electron donating anion-dependent through photoinduced electron transfer and ground-state charge transfer. Associated with cooperative protonation, the proton conductivity of the MOF is abruptly enhanced at low pH by two orders, but overhigh acid concentration is adverse because excessive anions can interrupt the conducting networks. Our work shows new perspectives of binding cooperativity in MOFs and should shed new light on the development of responsive fluorescent MOFs and proton conductive materials.
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•A comprehensive and state-of-art review on C(sp)-H carboxylation with CO2 is presented.•Much attention has been paid to metal catalysts, including those supported by porous ...solids.•The budding study of organocatalysis for the reaction is included.•The challenges and perspectives are discussed from academic and practical points of view.
Carbon dioxide (CO2) is the dominant greenhouse gas and the most abundant and renewable C1 resource. Therefore, the chemical fixation and conversion of CO2 to high-value chemicals and materials is an intriguing strategy towards carbon neutrality and sustainable chemical industry. The direct carboxylation of C(sp)-H bonds with CO2 has attracted great interest in the last decade as an atom-economic approach to propiolic acids, which have a wide range of applications in pharmaceuticals and advanced materials. This article provides a comprehensive review of this growing field of research. With a brief overview of non-catalytic carboxylation, the focus is on catalytic processes, which overwhelmingly involve metal catalysts, homogeneous or heterogeneous. The recently budding organocatalysis is also included. Critical comparisons and mechanism analyses are provided, along with personal perspectives for future studies.
The development of selective sensing materials for amine detection has received considerable attentions because amines have high toxicity and exist widely. In this article, we demonstrate for the ...first time that a degree of discriminative detection of alkylamines can be achieved by a metal–organic coordination material. The material is derived from CdII and 4,4′-bipyridinium-1,1′-bis(phenylene-3-carboxylate), shows 1D channels lined with electron-deficient viologen chromophores, and exhibits different colors upon contact with amine vapors of different molecular sizes and types (primary, secondary, and tertiary). The vapochromism is attributable to electron transfer from the amine group to viologen. The discrimination between amines is because the analyte–receptor interactions, which either directly mediate or indirectly affect electron transfer, are influenced by the number of the N–H bonds in the amine molecule, the size of the amine molecule relative to the receptor channel and the steric hindrance for the electron donor–acceptor contacts. The material also shows reversible photo- and hydrochromism owing to stimuli-induced reversible electron transfer. The compound can be deposited in paper simply by spraying the mixture solution of the starting metal salt and the ligand. The paper can be used as portable test strips for visual and differentiable detection of amines and as erasable inkless printing medium.
While viologen derivatives have long been known for electrochromism and photochromism, here we demonstrated that a viologen-carboxylate zwitterionic molecule in the crystalline state exhibits ...piezochromic and hydrochromic behaviors. The yellow crystal undergoes a reversible color change to red under high pressure, to green after decompression, and finally back to yellow upon standing at ambient pressure. Ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance X-ray diffraction and DFT calculations suggested that the piezochromism is due to the formation of radicals
pressure-induced electron transfer from carboxylate to pyridinium, without a crystallographic phase transition. It was proposed that electron transfer is induced by pressure-forced reduction of intermolecular donor-acceptor contacts. The electron transfer can also be induced by dehydration, which gives a stable green anhydrous radical phase. The color change is reversible upon reabsorption of water, which triggers reverse electron transfer. The compound not only demonstrates new chromic phenomena for viologen compounds, but also represents the first example of organic mechanochromism and hydrochromism associated with radical formation
electron transfer.
•UiO-66-NH2 catalyzes the reaction of aldehydes with cyanoacetate or malononitrile.•The catalyst is heterogeneous, recyclable and shows size effects on substrates.•It is proposed that the activity ...may arise from a dual acid–base character.
The amino-functionalized metal–organic framework of Zr(IV) with 2-aminoterephthalate, UiO-66-NH2, was studied as a solid catalyst for Knoevenagel condensation. The material can efficiently catalyze the condensation reaction of benzaldehyde with ethyl cyanoacetate or malononitrile in highly polar solvents such as DMF, DMSO and ethanol. The catalytic system has also been tested for various aromatic aldehydes, the conversion easily reaching more than 90% under mild conditions. It was demonstrated that the catalytic process is heterogeneous and shows size effects, characteristic of a porous catalyst. The catalyst can be recycled without losing its framework integrity and catalytic activity. The catalytic activity has been compared with dimethyl 2-aminoterephthalate and the isostructural amino-free MOF (UiO-66). The superior performance of UiO-66-NH2 has been attributed to the site-isolated acid–base bifunctional character. It has been proposed that the Zr site in close proximity to the amino group activates aldehydes to promote the formation of aldimine intermediates from the aldehydes and the amino group.
Ionic metal–organic frameworks (IMOFs) that integrate synergistic Lewis‐acid sites (intrinsic metal centers of the frameworks) and nucleophilic anions (halides encapsulated within pores) are ...intriguing platforms for the design of fully heterogeneous catalytic systems for cycloaddition of CO2 to epoxides. A new, facile and versatile synthetic approach has been used to fabricate triazolium‐based IMOFs for the first time. The approach makes use of azide–alkyne click chemistry and subsequent N‐alkylation to post‐synthetically create a cationic triazolium ring and introduce exchangeable counteranions at the same time. The IMOFs are efficient and recyclable heterogeneous catalysts for CO2 conversion under mild and cocatalyst‐free conditions. In particular, the click‐accessible triazolium ring provides a handle to incorporate further functionality. The MIL‐101‐tzmOH‐Br catalyst, which integrates hydrogen‐bonding hydroxy groups besides metal centers and bromide anions, shows superior catalytic performance under mild conditions.
Click here to convert CO2! An ionic metal–organic framework (IMOF) bearing a CrIII center at the node, a hydroxy group grafted to the cationic linker and a bromide anion encapsulated within the pore is fabricated by facile azide–alkyne click chemistry. The multifunctional IMOF presents superior heterogeneous catalytic activity for cycloaddition of CO2 to epoxides under mild and cocatalyst‐free conditions.
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