Conversion of Propargylic Amines with CO2 Catalyzed by a Highly Stable Copper(I) Iodide Thorium-Based Heterometal-Organic Framework.

The conversion of CO2 to generate high-value-added chemicals has become one of the hot research topics in green synthesis. Thereinto, the cyclization reaction of propargylic amines with CO2 is highly attractive because the resultant oxazolidinones are widely found in pharmaceutical chemistry. Cu(I)-based metal-organic frameworks (MOFs) as catalysts exhibit promising application prospects for CO2 conversion. However, their practical application was greatly limited due to Cu(I) being liable to disproportionation or oxidization. Herein, the solid copper(I) iodide thorium-based porous framework {[Cu5I6Th6(µ3-O)4(µ3-OH)4(H2O)10(L)10]·OH·4DMF·H2O}n (1) (HL = 2-methylpyridine-4-carboxylic acid) constructed by [Th6] clusters and [CuxIy] subunits was successfully prepared and structurally characterized. To our knowledge, this is the first copper(I) iodide-based actinide organic framework. Catalytic investigations indicate that 1 can effectively catalyze the cyclization of propargylic amines with CO2 under ambient conditions, which can be reused at least five times without a remarkable decline of catalytic activity. Importantly, 1 exhibits excellent chemical stability and the oxidation state of Cu(I) in it can remain stable under various conditions. This work can provide a valuable strategy for the synthesis of stable Cu(I)-MOF materials.

Silver Metal-Organic Framework Derived N-Doped Carbon Nanofibers for CO2 Conversion into ß-Oxopropylcarbamates.

Developing efficient heterogeneous catalysts for chemical fixation of CO2 to produce high-value-added chemicals under mild conditions is highly desired but still challenging. Herein, we first reported an approach to prepare a novel catalyst (Ag@NCNFs), featuring Ag nanoparticles (NPs) embedded within porous nitrogen-doped carbon nanofibers (NCNFs), via growing a Ag metal-organic framework on one-dimensional electrospun nanofibers followed by pyrolysis. Benefiting from the abundant nitrogen species and porous structure, Ag NPs is well dispersed in the obtained Ag@NCNFs. Catalytic studies indicated that Ag@NCNFs exhibited excellent catalytic activity for the three-component coupling reaction of CO2, secondary amines, and propargylic alcohols to generate ß-oxopropylcarbamates under mild conditions with a turnover number (TON) of 16.2, and it can be recycled and reused at least 5 times without an obvious decline in catalytic activity. The reaction mechanism was clearly clarified by FTIR, NMR, 13C isotope labeling, control experiments, and density functional theory calculations. The results suggest that Ag@NCNFs and 1,8-diazabicyclo[5.4.0]undec-7-ene can synergistically activate propargylic alcohol to react with CO2, and then the generated α-alkylidene cyclic carbonate was invaded by secondary amine to produce ß-oxopropylcarbamate. Importantly, to the best of our knowledge, this is the first experimental and theoretical investigation on this reaction.

Bifunctional Lanthanide-Based Coordination Polymers: Conversion of CO2 and Highly Selective Luminescence Sensing for Acetylacetone.

A series of bifunctional Ln(III)-based coordination polymers (CPs) {Ln(L)(DMA)2(NO3)}n [Ln(III) = Eu (1), Gd (2), and Dy (3); organic ligand H2L = 2,2'-(1,3,5,7-tetrahydroxyoctahydro-4,8-ethanopyrrolo[3,4-f]isoindole-2,6(1H,3H)-diyl)diacetic acid)] have been successfully synthesized. CPs 1-3 are isostructural and constructed from the dimeric Ln2 unit in which two adjacent LnIII ions are bridged by two µ3-carboxyl oxygens, and the Ln2 dimeric unit is connected by two NO3- ions, four DMA molecules, and four completely protonated L2- ligands forming a 2D layer structure. The magnetic research reveals that CP 2 shows a significant cryogenic magnetocaloric effect (-ΔSm = 22.9 J kg-1 K-1; T = 2.0 K and ΔH = 7.0 T), whereas CP 3 exhibits slow magnetic relaxation property under Hdc = 0 Oe field. Additionally, the luminescence explorations revealed that CP 1 can act as a recyclable luminescent probe for pollutant acetylacetone among various small organic solvent molecules, and the corresponding detection limit is 10-7 mol/L. More importantly, CP 1 also exhibits good catalytic performance in the cycloaddition reaction of CO2 and epoxides or cyanamides under mild conditions. As far as we know, CP 1 represents the first bifunctional lanthanide homogeneous catalyst that can efficiently catalyze the reaction of cyanamides/epoxides with CO2 simultaneously.

Highly Efficient Conversion of Propargylic Alcohols and Propargylic Amines with CO2 Activated by Noble-Metal-Free Catalyst Cu2 O@ZIF-8.

The cyclization reactions of propargylic alcohols and propargylic amines with CO2 are important in industrial applications, but it was a great challenge that non-noble-metal catalysts catalyzed both reactions under mild conditions. Herein, the catalyst Cu2 O@ZIF-8 was prepared by encapsulating Cu2 O nanoparticles into robust ZIF-8, and it can effectively catalyze the cyclization of both propargylic alcohols and propargylic amines with CO2 into valuable α-alkylidene cyclic carbonates and oxazolidinones with turnover numbers (TONs) of 12.1 and 19.6, which can be recycled at least five times. The mechanisms were further uncovered by NMR, FTIR, 13 C isotope-labeling experiments and DFT calculations, in which Cu2 O and DBU can synergistically activate the C≡C bond and the hydroxy/amino group of substrates. Importantly, it is the first example of a noble-metal-free catalyst that can catalyze both propargylic alcohols and propargylic amines with CO2 simultaneously.

Non-Noble-Metal Metal-Organic-Framework-Catalyzed Carboxylative Cyclization of Propargylic Amines with Atmospheric Carbon Dioxide under Ambient Conditions.

The coupling reaction of propargylic amines and carbon dioxide (CO2) to synthesize 2-oxazolidinones is an important reaction in industrial production, and yet harsh reaction conditions and noble-metal catalysts are often required to achieve high product yields. Herein, one novel noble-metal-free three-dimensional framework, [Mg3Cu2I2(IN)4(HCOO)2(DEF)4]n (1), assembled by magnesium and copper clusters was synthesized and applied to this reaction. Compound 1 displays excellent solvent stability. Importantly, 1, acting as heterogeneous catalyst, can highly catalyze the cyclization of propargylic amines with CO2 under atmospheric pressure at room temperature, which can be recycled at least five times without an obvious decrease of the catalytic activity. NMR spectroscopy, coupled with 13C-isotope- and deuterium-labeling experiments, clearly clarifies the mechanism of this catalytic system: CO2 was successfully captured and converted to the product of 2-oxazolidinones, the C≡C bond of propargylic amines can be effectively activated by 1, and proton transfer was involved in the reaction process. Density functional theory calculations are further conducted to uncover the reaction path and the crucial role of compound 1 during the reaction.

A Porous Copper-Organic Framework Assembled by [Cu12] Nanocages: Highly Efficient CO2 Capture and Chemical Fixation and Theoretical DFT Calculations.

A new porous copper-organic framework assembled from 12-nuclear [Cu12] nanocages {[Cu2(L4-)(H2O)2]·4DMA·2H2O}n (1) (H4L = 5,5'-(butane-1,4-diyl)-bis(oxy)-diisophthalic acid) was successfully prepared and structurally characterized. Compound 1 feathering of a 3D framework with two types of 1D nanotubular channels and a large specific surface area can effectively enrich various harmful dyes. Additionally, due to the carbon dioxide (CO2) interactions with open Cu(II) sites and the electron-rich ether oxygen atoms of ligand in 1, it exhibits a highly selective CO2 uptake. Interestingly, 1 can effectively catalyze the cycloaddition reaction of CO2 with various epoxides under mild conditions, which is ascribed to the Lewis acid Cu(II) sites in the framework of 1. Importantly, 1 acting as a heterogeneous catalyst can be recycled at least 10 times without an obvious loss of catalytic activity, and the CO2 cycloaddition mechanism was further uncovered by density functional theory (DFT) calculations. This study can greatly enrich the MOF catalysts system of CO2 conversion and also provide a valuable guidance for the design of efficient MOFs catalysts.

Solvent-Dependent Assembly and Magnetic Relaxation Behaviors of [Cu4I3] Cluster-Based Lanthanide MOFs: Acting as Efficient Catalysts for Carbon Dioxide Conversion with Propargylic Alcohols.

Two structurally similar metal-organic frameworks (MOFs) [Dy2Cu4I3(IN)7(DMF)2]·DMF (1) and [Dy2Cu4I3(IN)7(DMA)2]·DMA (2) (HIN = isonicotinic acid) feathering different coordinated solvent molecules were successfully isolated by tuning the types of solvents in the reaction system. Structural tests indicate that 1 and 2 are both built from 1D Dy(III) chains and copper iodide clusters [Cu4I3], generating into three-dimensional frameworks with an open 1D channel along the a axis. 1 and 2 display extensive and excellent solvent stability. Magnetic studies of 1 and 2 indicate that they exhibit interesting solvent-dependent magnetization dynamics. Importantly, 1 and 2 can act as highly effective catalysts for the carboxylic cyclization of propargyl alcohols with carbon dioxide (CO2) under ambient operating conditions. Additionally, the substrate scope was further explored over compound 1 based on the optimal conditions, and it exhibits efficient cyclic carboxylation of various terminal propargylic alcohols with CO2. This research offers an effective approach for the solvent-guided synthesis of MOFs materials and also presents the great application value of MOFs in CO2 chemical conversion.

An Ultrastable Matryoshka [Hf13 ] Nanocluster as a Luminescent Sensor for Concentrated Alkali and Acid.

Stable metal clusters that can resist both highly concentrated acid and alkali are unknown. Herein, we present a discrete neutral cluster, Hf13 (µ4 -O)8 (OCH3 )36 (1), which features extraordinary chemical stability by preserving its crystalline state in concentrated aqueous solutions of both acid (10 m HNO3 ) and alkali (20 m boiling NaOH). Importantly, 1 can serve as a luminescent probe for detecting both concentrated alkali (20 m NaOH) and strong acid (1 m HNO3 ) with high selectivity and repeatability. DFT studies of the electronic structure and bonding revealed that 1 has an extremely large HOMO-LUMO gap due to strong d π-p π bonding that accounts for the ultrahigh stability.

Metal-Organic Frameworks with Tb4 Clusters as Nodes: Luminescent Detection of Chromium(VI) and Chemical Fixation of CO2.

Two multifunctional metal-organic frameworks based on cubane-like tetrahedron Tb4 clusters as nodes have been synthesized and characterized. Compound 1 exhibits a 2D lanthanide-organic framework with Tb4 clusters as nodes, and compound 2 possesses a 3D framework with Tb4 clusters and Mn2+ as nodes. Interestingly, luminescent investigations on them reveal that the two compounds can act as recyclable luminescent probes for chromium(VI) anion species and the corresponding detection limit can reach 10-7 mol/L. Furthermore, 1 and 2 own efficient catalytic activity for the chemical fixation of CO2 with epoxides under mild conditions. Importantly, they both can be recycled at least three times without compromising the activity.

A Semi-Conductive Copper-Organic Framework with Two Types of Photocatalytic Activity.

Based on the newly designed ligand 4'-(3,5-dicarboxyphenyl)-4,2':6',4''-terpyridine (DCTP), a unique semi-conductive 3D framework {[Cu(Ι)Cu(ΙΙ)2(DCTP)2]NO3⋅1.5 DMF}n (1) with a narrow band gap of 2.1 eV, was obtained and structurally characterized. DFT calculations with van de Waals correction employed to explore the electronic structure of 1, clearly revealed its semi-conductive behavior. Furthermore, we found that 1 exhibits a superior band alignment with water to produce hydrogen and degrade organic pollutants. Without adding any photosensitizers, 1 displays an efficiently photocatalytic hydrogen production in water based on the photo-generated electrons under UV/Vis light. 1 also exhibits excellent photo-degradation of methyl blue under visible-light owing to the strong oxidization of excited holes. It is the first example of MOFs with doubly photocatalytic activities related to photo-generated electrons and holes, respectively.

Unique Chiral Interpenetrating d-f Heterometallic MOFs as Luminescent Sensors.

One novel three-dimensional (3D) 3d-4f metal-organic framework (MOF), [TbZn(L)(CO3)2(H2O)]n (1) [HL = 4'-(4-carboxyphenyl)-2,2':6',2″-terpyridine], has been successfully synthesized and structurally characterized. Structural analysis shows that compound 1 features a unique chiral interpenetrating 3D framework for the first time. The resulting crystals of 1 are composed of enantiomers 1a (P41) and 1b (P43), as was clearly confirmed by the crystal structure and the corresponding circular dichroism (CD) analyses of eight randomly selected crystals. The investigations on CD spectra based on every single crystal clearly assigned the Cotton effect signals. The powder X-ray diffraction measurement of 1 after being immersed in common solvents reveals that 1 possess excellent solvent stability. Furthermore, luminescent studies imply that 1 displays highly selective luminescent sensing of aldehydes, such as formol, acetaldehyde, and propanal.

Highly Efficient Conversion of Aziridines and CO2 Catalyzed by Microporous [Cu12] Nanocages.

The conversion of CO2 as a C1 source into value-added products is an attractive alternative in view of the green synthesis. Among the reported approaches, the cyclization reaction of aziridines with CO2 is of great significance since the generated N-containing cyclic skeletons are extensively found in pharmaceutical chemistry and industrial production. However, a low turnover number (TON) and homogeneous catalysts are often involved in this catalytic system. Herein, one novel copper-organic framework {[Cu2(L4-)(H2O)2]·3DMF·2H2O}n (1) (H4L = 2'-fluoro-[1,1':4',1″-Terphenyl]-3,3″,5,5″-tetracarboxylic acid) assembled by nanosized [Cu12] cages was successfully synthesized and structurally characterized, which exhibits high CO2/N2 selectivity due to the strong interactions between CO2 and open Cu(II) sites and ligands in the framework. Catalytic investigations suggest that 1 as a heterogeneous catalyst can effectively catalyze the cyclization of aziridines with CO2, and the TON can reach a record value of 90.5. Importantly, 1 displays excellent chemical stability, which can be recycled at least five times. The combination explorations of nuclear magnetic resonance (NMR), 13C-isotope labeling experiments, and density functional theory (DFT) clearly uncover the mechanism of this aziridine/CO2 coupling reaction system, in which 1 and tetrabutylammonium bromide (TBAB) can highly activate the substrate molecule, and the synergistic catalytic effect between them can greatly reduce the reaction energy barrier from 51.7 to 36.2 kcal/mol.

Two novel Ln8 clusters bridged by CO32- effectively convert CO2 into oxazolidinones and cyclic carbonates.

It is difficult and challenging to design and construct high-nuclearity Ln(III)-based clusters due to the high coordination numbers and versatile coordination geometries of Ln(III) ions. Herein, two novel octanuclear Ln(III)-based clusters [Ln8(H2L-)4(HL2-)4(NO3)6 (CO3)2](NO3)2·2CH3CN (Ln = Nd (1) and Sm (2)) have been synthesized under solvothermal conditions. The X-ray single analysis reveals that both 1 and 2 are octanuclear structures and the eight central Ln(III) ions are bridged by two CO32- anions. Catalytic study revealed that 1 and 2 can effectively catalyze the cycloaddition reaction of CO2 and aziridines or epoxides simultaneously under mild conditions. What is more, cluster 1, as a heterogeneous catalyst, can be reused at least three times without obvious loss in catalytic activity for coupling of CO2 and epoxides. To our knowledge, cluster 1 is the first Ln(III)-based cluster catalyst used for the conversion of CO2 with aziridines or epoxides simultaneously. This work provides a successful strategy to integrate high-nuclear Ln(III)-based clusters for CO2 conversion, which may open a new space for the construction of multifunctional high-nuclear Ln(III)-based clusters as efficient catalysts for CO2 conversion.

Self-assembly of octanuclear Ln(III)-based clusters: their large magnetocaloric effects and highly efficient conversion of CO2.

The design and construction of high-nuclear lanthanide clusters with fascinating topology and functional properties have been an active area of research, however, the development of an effective approach for obtaining high-nuclear lanthanide clusters with multifunctional properties is still extremely difficult. Up to now, a systematic approach for guiding the further expansion of Ln(III)-based clusters showing good functional properties is lacking. Herein, we design and synthesize a polydentate Schiff base ligand (HL), which reacts with ß-diketonate salts Ln(acac)3·2H2O, and a series of Ln8 clusters [Ln8(acac)6(L)2(µ3-O)6(µ2-C2H5O)4(µ2-Hacac)2]·2CH3CN (Ln(III) = Gd (1), Dy (2), and Ho (3); HL = pyridine-2-carboxylic acid (5-hydroxymethyl-furan-2-ylmethylene)-hydrazide, Hacac = acetylacetone) have been successfully synthesized. Single-crystal X-ray diffraction studies reveal that clusters 1-3 are isostructural and can be viewed as a Ln8 core bridged by eighteen µ2-O atoms, six µ3-O atoms and two µ4-O atoms. Magnetic studies show that cluster 1-Gd8 displays a large magnetocaloric effect with -ΔSm = 46.14 J kg-1 K-1 (T = 2.0 K and ΔH = 7.0 T); cluster 2-Dy8 exhibits single-molecule magnet behavior under zero-field conditions. It is worth mentioning that the -ΔSm of cluster 1-Gd8 is larger than that of most reported polynuclear Gd(III)-based clusters; the 2-Dy8 cluster is one of the rare polynuclear Lnn SMMs (n ≥ 8) under zero dc field. Importantly, these Ln(III)-based clusters (1-3) can catalyze the cycloaddition of CO2 with epoxides with high efficiency under mild conditions; and cluster 1-Gd8 as a catalyst could be reused at least three times without obvious loss of catalytic performance.

Molecular assemblies from linear-shaped Ln4 clusters to Ln8 clusters using different ß-diketonates: disparate magnetocaloric effects and single-molecule magnet behaviours.

A series of tetranuclear lanthanide-based clusters [Ln4(dbm)6(L)2(CH3OH)4]·2CH3OH (Ln(III) = Gd (1), Dy (2), and Ho (3); H3L = 2-[(2-(hydroxyimino)propanehydrazide)methyl]-2,3-dihydroxybenzaldehyde, Hdbm = dibenzoylmethane) and octanuclear lanthanide-based clusters [Ln8(HL)10(CH3O)4(CH3OH)2]·6CH3OH (Ln(III) = Gd (4), Dy (5)) were assembled using a polydentate Schiff-base ligand H3L and two different ß-diketone salts via a solvothermal method, and their structures and magnetic properties have been characterized. Interestingly, ß-diketones play an important role in assembling and affecting the structures of Ln4 to Ln8 clusters. This is the first use of ß-diketone to affect the structures of polynuclear Ln(III)-based clusters from linear-shaped Ln4 clusters to Ln8 clusters. Magnetic studies revealed that antiferromagnetic interactions exist in clusters 1-Gd4 and 4-Gd8. More importantly, clusters 1-Gd4 and 4-Gd8 display significant cryogenic magnetic refrigeration properties (-ΔSm = 24.88 J kg-1 K-1 for 1-Gd4 and -ΔSm = 32.52 J kg-1 K-1 for 4-Gd8); the results show that cluster 4-Gd8 exhibits a larger magnetocaloric effect than 1-Gd4. Cluster 2-Dy4 shows remarkable single-molecule magnet (SMM) behavior (ΔE/kB = 67.5 K and τ0 = 3.06 × 10-7 s) under a zero dc field, and 5-Dy8 exhibits a field-induced SMM-like behavior (ΔE/kB = 39.83 K and τ0 = 2.12 × 10-7 s) under a 5000 Oe dc field.

Linear-shaped Ln and Ln clusters constructed by a polydentate Schiff base ligand and a ß-diketone co-ligand: structures, fluorescence properties, magnetic refrigeration and single-molecule magnet behavior.

Herein, ten new linear-shaped LnIII4 and LnIII6 clusters, with the formula [Ln4(acac)6L2(CH3O)2(CH3OH)4]·xCH3OH (Ln = Nd (1), Sm (2), Eu (3), Gd (4), Tb (5), Dy (6), and Tm (8), Hacac = acetylacetone), [Ln6(acac)4L4(CH3O)6]·xCH3OH (Er (7) and Yb (9)), and [Lu4(acac)6L2(OH)2]·2CH2Cl2 (10), based on a polydentate Schiff base ligand, H2L, and a ß-diketone co-ligand were successfully synthesized and structurally characterized. Single crystal X-ray diffraction measurements reveal that the structures of the clusters 1-6, 8 and 10 are very similar and their central Ln(iii) ions are linearly arranged Ln4; however, the clusters 7 and 9 possess a rare linearly arranged Ln6. The investigations on the solid-state fluorescence properties show that the clusters 2, 3, 5 and 6 display the characteristic lanthanum luminescence at room temperature. Magnetic studies reveal that weak antiferromagnetic interactions exist between adjacent Gd(iii) ions in cluster 4. More importantly, the cluster 4 exhibits significant MCE with the maximum -ΔSm value of 27.96 J kg-1 K-1 at 2.0 K and 7.0 T, whereas the cluster 6 displays a slow magnetic relaxation behavior under a zero dc field with the effective energy barrier ΔE/kB = 8.64 K and τ0 = 6.98 × 10-6 s.

pH-induced Dy4 and Dy10 cluster-based 1D chains with different magnetic relaxation features.

Two novel tetra- and deca-nuclear dysprosium compounds, namely, [Dy4(µ3-OH)2(L)10(bipy)2(H2O)2]n (1) and {[Dy10(µ3-OH)8(L)22(bipy)2(H2O)2]·5H2O}n (2) (L = 3-fluoro-4-(trifluoromethyl)benzoic acid; bipy = 2,2'-bipyridine), have been successfully obtained by hydrothermal reaction at different pH values. The solid state structures of 1 and 2 were established by the single crystal X-ray diffraction technique, and both of them exhibit complicated 1D chains with [Dy4] (1) and [Dy10] (2) cluster units, respectively. Adjacent [Dy4] in 1 and [Dy10] in 2 are connected by two bridging carboxylate groups in the η(1):η(1):µ2 mode. Magnetic studies reveal that they exhibit different magnetic relaxation behaviors with the energy barrier of 23.6 K for 1 and 3.2 K for 2. Interestingly, the large divergence in both the structures and magnetic properties for 1 and 2 only originated from the different pH values in preparing them.