Cluster-based Metal-organic Frameworks Research Articles

Selective adsorption of Pd(II) over interfering metal ions (Co(II), Ni(II), Pt(IV)) from acidic aqueous phase by metal-organic frameworks

Metal-organic frameworks (MOFs) have successfully employed as a class of adsorbents for selective separation of CO2 and some organics from gas and liquid phases; however, little attention has been paid to MOFs applications for selective adsorption of ionic targets from aqueous solutions. Besides, selective separation of precious metals is of great importance from the standpoint of realizing a new sustainable development concept of “urban mining”. While, separation of precious metals is challenging, as they are often present in acidic solutions with many interfering metal ions. Herein, Zr(IV)-cluster-based MOFs were synthesized in this study for the selective adsorption of Pd(II), as a model precious metal ion, from acidic aqueous solutions containing Co(II), Ni(II), Pd(II), and Pt(IV). Among the various Zr-MOFs synthesized (i.e. UiO-66, UiO-66-NH2 and UiO-66-NHCOCH3), UiO-66-NH2 showed the highest Pd(II) selectivity, with the Pd(II) uptake in the mixture-metals solution being around 181 times higher than that of Pt(IV). The Pd(II) selectivity of UiO-66-NH2 was attributed to higher binding affinity of the protonated amino groups (–NH3+) for PdCl42− and more convenient diffusion of the PdCl42− through the apertures (pores) of the UiO-66-NH2 – which have the appropriate inner sizes befitting PdCl42− penetration – than for Pt(IV) ions (PtCl62−).

A Flexible Fluorescent SCC-MOF for Switchable Molecule Identification and Temperature Display

Flexible luminescent metal–organic frameworks (MOFs) sensitive to physical and chemical variation demonstrate potential application in sensing, but are commonly limited to ones incorporating specialized chromophores, so that the design, preparation, and reversible well-defined crystallographic transitions of such materials remain a great challenge. Here, an easily prepared flexible luminescent silver-chalcogenolate cluster-based metal–organic framework (SCC-MOF), Ag10bpy, exceptionally distinguishes chloromethanes CH2Cl2, CHCl3, and CCl4 by different fluorescent responsive signals, which originated from its crystalline dipole moment orientation relative to chromophores. Moreover, “glass-to-fluid” transition of the distinctly responsive species in the crystalline pore is demonstrated to modulate striking chromism with scarce segmented emission among MOFs, resulting from subtle dynamic solvation of chromophores. Retention of single crystallinity enables elucidation of the relationship between distinct fluor...

A new cluster-based metal-organic framework with triazine backbones for selective luminescent detection of mercury(II) ion

A new cluster-based metal–organic framework (MOF) [(Me2NH2)Cd3(OH)(H2O)3(TATAB)2](DMA)6 (1, DMA=N,N-dimethylacetamide) with triazine backbones has been successfully prepared using the 4,4′,4″-s-triazin-1,3,5-triyltri-p-aminobenzoic acid (H3TATAB) as the organic spaces. The as-prepared 1 was characterized by elemental analysis, powder X-ray diffraction, single-crystal X-ray diffraction and thermogravimetric analysis. The X-ray study result reveals that complex 1 belongs to the tetragonal space group P43212 and shows a three-dimensional channel-type framework. The luminescent responses of 1 respect to different metal ions were studied, which reveals that 1 shows highly selective and sensitive detection of Hg2+ via an obvious fluorescence quenching and red-shift of the emission peak. Furthermore, the possible sensing mechanism has also been discussed in this work.

Extending the Compositional Range of Nanocasting in the Oxozirconium Cluster-Based Metal–Organic Framework NU-1000—A Comparative Structural Analysis

The process of nanocasting in metal–organic frameworks (MOFs) is a versatile approach to modify these porous materials by introducing supporting scaffolds. The nanocast scaffolds can stabilize metal-oxo clusters in MOFs at high temperatures and modulate their chemical environments. Here we demonstrate a range of nanocasting approaches in the MOF NU-1000, which contains hexanuclear oxozirconium clusters (denoted as Zr6 clusters) that are suitable for modification with other metals. We developed methods for introducing SiO2, TiO2, polymeric, and carbon scaffolds into the NU-1000 structure. The responses of NU-1000 toward different scaffold precursors were studied, including the effects on morphology, precursor distribution, and porosity after nanocasting. Upon removal of organic linkers in the MOF by calcination/pyrolysis at 500 °C or above, the Zr6 clusters remained accessible and maintained their Lewis acidity in SiO2 nanocast samples, whereas additional treatment was necessary for Zr6 clusters to become ...

Multifunctional Metal–Organic Frameworks Based on Redox-Active Rhenium Octahedral Clusters

The redox-active rhenium octahedral cluster unit [Re6Se8(CN)6]4- was combined with Gd3+ ions and dicarboxylate linkers in novel types of metal-organic frameworks (MOFs) that display a set of functional properties. The hydrolytically stable complexes [{Gd(H2O)3}2(L)Re6Se8(CN)6]·nH2O (1, L = furan-2,5-dicarboxylate, fdc; 2, L = thiophene-2,5-dicarboxylate, tdc) exhibit a 3D framework of trigonal symmetry where 1D chains of [{Gd(H2O)3}2(L)]4+ are connected by [Re6Se8(CN)6]4- clusters. Frameworks contain spacious channels filled with H2O. Solvent molecules can be easily removed under vacuum to produce permanently porous solids with high volumetric CO2 uptake and remarkable CO2/N2 selectivity at room temperature. The frameworks demonstrate an ability for reversible redox transformations of the cluster fragment. The orange powders of compounds 1 and 2 react with Br2, yielding dark-green powders of [{Gd(H2O)3}2(L)Re6Se8(CN)6]Br·nH2O (3, L = fdc; 4, L = tdc). Compounds 3 and 4 are isostructural with 1 and 2 and also have permanently porous frameworks but display different optical, magnetic, and sorption properties. In particular, oxidation of the cluster fragment "switches off" its luminescence in the red region, and the incorporation of Br- leads to a decrease of the solvent-accessible volume in the channels of 3 and 4. Finally, the green powders of 3 and 4 can be reduced back to the orange powders of 1 and 2 by reaction with hydrazine, thus displaying a rare ability for fully reversible chemical redox transitions. Compounds 1-4 are mentioned as a new class of redox-active cluster-based MOFs with potential usage as multifunctional materials for gas separation and chemical contamination sensors.

Silver Thiolate Nano-sized Molecular Clusters and Their Supramolecular Covalent Frameworks: An Approach Toward Pre-templated Synthesis.

A series of seven new complexes including silver-thiolate molecular clusters and their covalent supramolecular frameworks have been assembled from the silver carbide precursor Ag2 C2 using a C22- pre-templated approach. Herein, two prototype clusters Ag14 (SR)6 and CO3 @Agm (SR)10 (R=isopropyl, cyclohexyl or tert-butyl; m=18 or 20) are employed to construct cluster-based metal-organic frameworks of different dimensions. In particular, both new ellipsoidal tetradecanuclear molecular cluster compounds, namely, Ag14 (S-iPr)6 (CO2 CF3 )8 ⋅(DMSO)6 (two polymorphic forms 1, 2) and [Ag14 (S-Cy)6 (CO2 CF3 )8 (DMSO)4 ]⋅(DMSO)3 (3), and a cluster-based metal-organic framework {Ag3 [Ag14 (S-iPr)6 (CO2 CF3 )11 (H2 O)3 CH3 OH]⋅(H2 O)2.5 }n (4) have been isolated and structurally characterized. Furthermore, increased acidity of the reaction mixture afforded three carboxylate-templated cluster based frameworks: a chain-like compound {[HN(CH3 )2 CO]⋅[CO3 @Ag18 (S-tBu)10 (NO3 )7 (DMF)4 ]⋅DMF}n (5), as well as two layer-type compounds, namely, {Ag[CO3 @Ag20 (S-iPr)10 (CO2 CF3 )9 (CO2 HCF3 )(CH3 OH)2 ]}n (6) and {Ag2 [CO3 @Ag20 (S-Cy)10 (CO2 CF3 )10 (CO2 HCF3 )2 (H2 O)2 ]⋅(H2 O)3 ⋅(CH3 OH)3 }n (7) exhibiting sql-net characteristics. It is demonstrated that the C≡C2- pre-template, which draws several Ag+ ions together to form the C2 @Agn entity, plays an indispensable role in the syntheses of these compounds. Furthermore, covalent linkage of these nano-sized silver thiolate clusters from one- to three-dimensions revealed enormous potential for the future development of silver cluster-based frameworks.

Unprecedented (4,6)-Connected Net with Mixed-Valence M2IIMIII Trinuclear and M6II Hexanuclear Clusters (M = Ni, Co): Syntheses, Crystal Structures, and Magnetic Properties

Two new cluster-based metal–organic frameworks (MOFs), {(M3OH)2[(M6O(OH)2(H2O)2]1.5(EBTC)6}·solvent (M = Ni and Co for 1 and 2, respectively), have been synthesized using a solvothermal reaction, where H4EBTC represents 1,1′-ethynebenzene-3,3′,5,′-tetracarboxylic acid. The isostructural 1 and 2 crystallize in the hexagonal space group P6/mmm, containing class III mixed-valence Ni2IINiIII/Co2IICoIII trinuclear and Ni6II/Co6II hexanuclear secondary building units (SBUs). Both SBUs possess the perfectly planar μ3-O2– and μ4-O2– bridging mode, respectively. In 1 and 2, two trinuclear and three hexanuclear clusters form a cage with the dimensions of ca. 5.0 × 5.0 × 7.8 A3, which align into a bamboo-like structure through sharing the trinuclear clusters along the c-axis, and form a honeycomb-like structure via sharing the hexanuclear clusters on the plane parallel to the crystallographic (001) plane. In addition, the magnetic properties have been further investigated for two MOFs, disclosing that the weakly ant...

Pentanuclear Yb(III) cluster-based metal-organic frameworks as heterogeneous catalysts for CO2 conversion

Two porous metal-organic frameworks (MOFs) incorporating pentanuclear Yb(III) clusters and pyridyl-supported tetracarboxylates or pyridyl carboxylic acid-supported tetracarboxylates, Yb-DDPY and Yb-DDIA, are presented, in which the pentanuclear Yb(III) cluster shows uncommon trigonal bipyramidal geometry. Furthermore, the pentanuclear Yb(III) clusters are extended by tetracarboxylates to form a 3D porous framework with uniform M12L8-cages constructed by 12 pentanuclear Yb(III) clusters and 8 tetracarboxylates with the size of ca. 20Å×17Å. Their highly CO2 uptake capacity and the existence of Lewis acidic sites make these MOFs promising catalysts for the chemical conversion of CO2. These MOFs demonstrate good catalytic activities and recyclability in the cycloaddition of CO2 and epoxides at 60°C under 1.0MPa pressure or at room temperature and atmospheric pressure. In addition, the synergistic effect of the Brønsted acidic –COOH groups and the Lewis acidic Yb(III) sites makes Yb-DDIA exhibit higher catalytic activity towards the cycloaddition of CO2 and epoxides.

A Distorted [Mn2(COO)4N2] Cluster Based Metal–Organic Framework with (3,3,6) Topology and Selective Adsorption of CO2

On the basis of the ligand of 5-(pyridin-3-yl)isophthalic acid (H2L), a new distorted [Mn2(COO)4N2] cluster based metal–organic framework with (3,3,6) topology, [Mn2(L)2DMF]·DMF·MeOH (NJU-Bai33; DMF = N,N- dimethylformamide), was synthesized, which exhibits a new point (Schlafli) symbol of (4·62)2(42·68·85), contains open metal sites, and shows selective adsorption of CO2 over N2 and CH4 with CO2 uptake amounts high up to 7.9 and 4.2 wt % at 0.15 bar and at 273 and 298 K, respectively.

Hypersensitive dual-function luminescence switching of a silver-chalcogenolate cluster-based metal-organic framework.

Silver(i) chalcogenide/chalcogenolate clusters are promising photofunctional materials for sensing, optoelectronics and solar energy harvesting applications. However, their instability and poor room-temperature luminescent quantum yields have hampered more extensive study. Here, we graft such clusters to adaptable bridging ligands, enabling their interconnection and the formation of rigid metal-organic frameworks. By controlling the spatial separation and orientation of the clusters, they then exhibit enhanced stability (over one year) and quantum yield (12.1%). Ultrafast dual-function fluorescence switching (<1 s) is also achieved, with turn-off triggered by O2 and multicoloured turn-on by volatile organic compounds. Single-crystal X-ray diffraction of the inclusion materials, obtained by single-crystal-to-single-crystal transformation, enables precise determination of the position of the small molecules within the framework, elucidating the switching mechanism. The work enriches the cluster-based metal-organic framework portfolio, bridges the gap between silver chalcogenide/chalcogenolate clusters and metal-organic frameworks, and provides a foundation for further development of functional silver-cluster-based materials.

Ag-NPs embedded in two novel Zn3/Zn5-cluster-based metal-organic frameworks for catalytic reduction of 2/3/4-nitrophenol.

By utilizing symmetrical pentacarboxylate ligands, 3,5-di(2',5'-dicarboxylphenyl)benzoic acid (H5L1) and 3,5-di(2',4'-dicarboxylphenyl)benzoic acid (H5L2), two novel porous Zn-MOFs, [Zn5(μ3-H2O)2(L1)2]·3DMA·4H2O (CTGU-3) and [Zn3(μ3-OH)L2(H2O)3]·H2O (CTGU-4) have been synthesized under solvothermal conditions. CTGU-3 and CTGU-4 exhibit 3D microporous frameworks with flu and dia topologies and possess unique secondary building units [Zn5(μ3-H2O)2(RCO2)6] and [Zn3(μ3-OH)(RCO2)3], respectively. Such porous systems create a unique space or surface to accommodate Ag nanoparticles (Ag NPs), which could efficiently prevent Ag NPs from aggregation and leaching. In this work, two new Ag@Zn-MOF composites, denoted as Ag@CTGU, have been successfully fabricated through solution infiltration, for the reduction of nitrophenol. Compared with CTGU-4, CTGU-3 shows enhanced catalytic efficiency toward the reaction when it is used as a catalyst support of Ag NPs. Moreover, gas sorption and luminescence properties of two compounds were also investigated.

Structure, solution assembly, and electroconductivity of nanosized argento-organic-cluster/framework templated by chromate.

In view of elucidating potential structures and assembly mechanism of silver clusters and silver cluster-based metal-organic frameworks, we prepared four argento-organic-clusters/frameworks where the structures were directed by chromate in the presence of different thiolates. All four structures with tBuC6H4S-, SiBu-, and SiPr- consist of three core-shells, an inner CrO42-, an intermediate Ag-S aggregate and finally the protective organic moieties. {(HNEt3)3[Ag(CrO4)4@Ag46(SC6H4tBu)24(CF3COO)18(DMF)4]} (1) is a supertetrahedron with an inner Ag(CrO4)4 tetrahedron shelled by four fused Ag11.5S6 lobes. [(CrO4)5@Ag40(SiBu)27(CF3COO)3]n (2) is an undulated snake-like tube housing the infinite CrO42- tetrahedra. [(CrO4)2@Ag41(SiBu)30(NO3)3(CN)4]n (3) forms an uncommon 7-connected kwh network incorporating hexagonal layers of Ag19(SiBu)15 balls with a single inner CrO42- connected by another Ag atom. Both enantiomeric chiral qtz frameworks of [CrO4@Ag20(SiPr)10(Cr2O7)2(COOCF3)4(DMF)4]n (4) were structurally characterized. In 4, Cr2O72- connects the Ag20(SiPr)10 clusters with a trapped CrO42- into a 3D quartz (qtz) structure, where the spherical cluster acts like oxygen and Cr2O72- takes the place of Si in SiO2. Electrospray ionization mass spectrometry (ESI-MS) analysis of the reaction solutions of 1-4 clearly indicated that (i) the Ag(CrO4)4@Ag46 core of 1 can retain its molecular structure in the solution and (ii) the chromate-templated polynuclear silver-thiolate species in solution are important building blocks to construct the 1D or 3D motif for 2-4. The electrochemistry in sulfuric acid and enhancement of the electrical conductivity upon I2 doping have also been reported.

Structures and applications of metal–organic frameworks featuring metal clusters

Metal–organic frameworks (MOFs), self-assembled from metal ions or metal clusters with organic ligands, are well known for their intriguing structure, permanent porosity, and tunable properties and have shown great prospect for various applications. In the present review, we mainly highlight recent significant examples of metal clusters in our team and provide a comprehensive review on the structure of metal cluster-based MOFs and their applications including for sensing metal ions, small molecules and gases, nitroaromatics and explosives, as well as many other applications. We classified two different coordination polymers: (i) homometallic coordination polymers (examples of coordination polymers with single and mixed types of secondary building units) and (ii) heterometallic coordination polymers (examples of coordination polymers based on metal–oxygen clusters and W–Cu–S clusters).

Two Li-Zn Cluster-Based Metal-Organic Frameworks: Strong H2/CO2 Binding and High Selectivity to CO2.

Two metal-organic frameworks (MOFs) {(Me2NH2)[ZnLi(PTCA)(H2O)]}n·n{3DMF·C4H8O2·4H2O} (1) and {(Me2NH2)[ZnLi(PTCA)]}n·n{3DMF·5H2O} (2) have been constructed from Li-Zn clusters and pyrene-1,3,6,8-tetracarboxylic acid (H4PTCA) under solvothermal conditions. Gas sorption measurements have revealed that the pore of desolvated 2 (2d) can strongly interact with H2 and CO2, with high H2 and CO2 adsorption heats of 15.3 and 51.9 kJ/mol, respectively. Furthermore, 2d can selectively adsorb CO2 over N2 and CH4, with high adsorption selectivity of CO2/N2 and CO2/CH4.

Microporous Hexanuclear Ln(III) Cluster-Based Metal-Organic Frameworks: Color Tunability for Barcode Application and Selective Removal of Methylene Blue.

Two hexanuclear Ln(III) cluster-based metal-organic frameworks (MOFs) (Ln = Tb or Eu) and a series of isomorphic bimetallic Ln(III)-MOFs have been synthesized by changing the ratio of Tb(III) and Eu(III) under solvothermal conditions. The excellent linear color tunability (from green to red) makes them suitable for barcode application. In addition, the anionic Ln(III)-MOFs exhibit superior uptake capacity toward methylene blue (MB+) by an ion-exchange process, and its reversible adsorption performance makes 1 suitable for removal of organic dye MB+. The as-prepared anionic hexanuclear Ln(III) cluster-based MOFs can serve as a multifunctional material for an optical and environmental area.

One-Dimensional Helical Metal Coordination Polymer: Synthesis and Structure of Infinite Chain of [Ag7(S2CNEt2)6] n + (as [SbF6]− salt) Composed of Ag6(S2CNEt2)6 Cluster Units Linked by Ag(I) Ions via Peculiar Chelating S–S Bites

A new polymeric silver cluster, formulated as [Ag7(S2CNEt2)6][SbF6] (1) was synthesized and characterized by single-crystal X-ray crystallography. The structure can be described as an infinite cationic polymeric helical chain consisting of two [Ag6(S2CNEt2)6] clusters linked by a silver ion tetrahedrally coordinated with four sulfur atoms, two from each of the constituent clusters. The stereochemistry of 1 is classified as a new ζ-modification of silver dithiocarbamate cluster. It is suggested that the constituent [Ag6(S2CNEt2)6] clusters in 1 can be used as building blocks in the construction of 1-D cluster-based metal coordination polymers as well as 2-D or 3-D cluster-based metal–organic frameworks. The paper reports the synthesis and single-crystal structure of an infinite helical chain of a cationic metal coordination polymer consisting of two [Ag6(S2CNEt2)6] clusters linked by a tetrahedrally coordinated silver ion. The implication of the utility of the constituent [Ag6(S2CNEt2)6] clusters as building blocks in the construction of other 1-D cluster-based metal coordination polymer as well as 2-D or 3-D cluster-based metal–organic-frameworks is discussed.

Beyond Clusters: Supramolecular Networks Self-Assembled from Nanosized Silver Clusters and Inorganic Anions.

Assembly of small clusters into rigid bodies with precise shape and symmetry has been witnessed by the significant advances in cluster-based metal-organic frameworks (MOFs), however, nanosized silver cluster based MOFs remain largely unexplored. Herein, two anion-templated silver clusters, CO3 @Ag20 and SO4 @Ag22 , were ingeniously incorporated into a 2D sql lattice (1, [CO3 @Ag20 (iPrS)10 (NO3 )8 (DMF)2 ]n ) and an unprecedented 3D two-fold interpenetrated dia network (2, [SO4 @Ag22 (iPrS)12 (NO3 )6 ⋅2 NO3 ]n ), respectively, under mild solvothermal conditions. Their atomically precise structures were confirmed by single-crystal X-ray diffraction analysis and further consolidated by IR spectroscopy, thermogravimetric analysis (TGA), and elemental analysis. Each drum-like CO3 @Ag20 cluster is extended by twelve NO3 (-) ions to form the 2D sql lattice of 1, whereas each ball-shaped SO4 @Ag22 cluster with a twisted truncated tetrahedral geometry is pillared by four [Ag6 (NO3 )3 ] triangular prisms to form the 3D interpenetrated dia network of 2. Notably, 2 is the first interpenetrated 3D MOF constructed from silver clusters. These results demonstrate the dual role of the anions, which not only internally act as anion templates to induce the formation of silver thiolate clusters but also externally extend the cluster units into the rigid networks. The photoluminescent and electrochemical properties of 2 are discussed in detail.

Switching a 2D Co(II) layer to a 3D Co7-cluster-based metal-organic framework: syntheses, crystal structures, and magnetic properties.

Two 2D layered coordination networks with formulas of {[Co(TPA)Cl](H2O)2.5}n (1) and {[Co(TPA)(μ2-OH)](H2O)2}n (2) (HTPA = 4-(1,2,4-triazol-4-yl)phenylacetic acid) were solvothermally synthesized and fully characterized. Interesting 1D Co(2+)-Cl or Co(2+)-μ2-OH chain structures were observed. By carefully adjusting the reaction conditions, a new 3D metal-organic framework (MOF) with a formula of {[Co7(TPA)6(μ3-OH)4(μ2-OH)2(H2O)4](TPA)2(DMF)3(H2O)3}n (3) was obtained. MOF 3 is built from Co7 clusters and fully deprotonated TPA ligands, which display a cubic pcu topology. Factors that influence the structures of the three TPA-based complexes, as well as their magnetic properties, were investigated in detail. The heptanuclear-Co(II)-cluster-based MOF 3 shows interesting magnetization dynamics at low temperature.

A tetranuclear [Co4] cluster-based metal–organic framework: Synthesis, structure and magnetic property

A CoII coordination polymer, {[Co4(CIPA)2(μ3-OH)2(H2O)4]·4H2O}n (1), based on a tri-carboxylate ligand (H3CIPA=5-acetyloxybenzene −1,3-dicarboxylic acid) has been obtained and characterized structurally. Compound 1 displays a two-dimensional (2D) framework based on [Co4] clusters. Thermogravimetric analysis suggests high thermal stability of compound 1, and magnetic properties measurement indicates that antiferromagnetic couplings exist between neighboring CoII centers.

Cluster-based metal–organic frameworks as sensitive and selective luminescent probes for sensing nitro explosives

Employing a C3 symmetric ligand, one new cluster-based MOF [Cd2.5Na(NTB)2(DMF)4]·3DMF (1) has been successfully obtained. The results reveal that compound 1 could be applied as a fluorescence sensor for TNP with high sensitivity and selectivity.