Showing papers on "Polyoxometalate published in 2013"
TL;DR: The coexistence of both the chiral directors and the oxidants within a confined space provided a special environment for the formation of reaction intermediates in a stereoselective fashion with high selectivity.
Abstract: Chiral metal–organic frameworks (MOFs) with porous and tunable natures have made them feasible for performing a variety of chemical reactions as heterogeneous asymmetric catalysts. By incorporating the oxidation catalyst [BW12O40]5– and the chiral group, l- or d-pyrrolidin-2-ylimidazole (PYI), into one single framework, the two enantiomorphs Ni-PYI1 and Ni-PYI2 were obtained via self-assembly, respectively. The channels of Ni-PYIs were enlarged through a guest exchange reaction to remove the cationic chiral templates and were well modulated with hydrophilic/hydrophobic properties to allow molecules of both H2O2 and olefin ingress and egress. The coexistence of both the chiral directors and the oxidants within a confined space provided a special environment for the formation of reaction intermediates in a stereoselective fashion with high selectivity. The resulting MOF acted as an amphipathic catalyst to prompt the asymmetric dihydroxylation of aryl olefins with excellent stereoselectivity.
302 citations
TL;DR: In this paper, the first cobalt-containing Keggin polyoxometalate (K7[CoIIICoII(H2O)W11O39] (1) was tested as the first KG catalyst for efficient O2 production via both visible-light driven and thermal water oxidation.
Abstract: Water-soluble K7[CoIIICoII(H2O)W11O39] (1) was tested as the first cobalt-containing Keggin polyoxometalate catalyst for efficient O2 production via both visible-light driven and thermal water oxidation. Under the optimal photocatalytic conditions [photoirradiation at λ ≥ 420 nm, [Ru(bpy)3]Cl2 as the photosensor, Na2S2O8 as the oxidant in borate buffer (pH = 9.0)],the turnover number (TON) can reach as high as 360, the initial quantum yield and the initial turnover frequency (TOF) for the first 60 seconds was 27% and 0.5 s−1, respectively. Variables of the photocatalytic reaction, including catalyst concentrations, buffer types and concentrations, pHs, dye concentrations, oxidant concentrations, etc., were systemically studied. The oxygen atoms of the evolved oxygen came from water, as confirmed by isotope-labeled experiments. In the thermal water oxidation, the TON and oxygen yield were measured to be 15 and 60%, respectively. The stability of 1 was tested and confirmed with multiple experiments (laser flash photolysis, DLS, CV, FT-IR, EDX, and catalyst recycling) within the photocatalytic water oxidation duration, which ruled out the possibility that neither the free Co2+ ions were present in the reaction solution nor were cobalt oxide/hydroxide nanoparticles in situ formed from the assumed decomposition of 1. All the evidence stated here collectively supports that 1 is the true molecular catalyst. In addition, the recycled sample was reused for water oxidation catalysis and showed similar catalytic behaviors (kinetics and activity) to that of the freshly prepared catalyst. No insoluble forms where found when the borate buffer solution of 1 was aged for 2 months, whereas its analogue, K8[CoIICoII(H2O)W11O39] (4), is rapidly decomposed to a blue-purple cobalt oxide precipitate in borate buffer. The stability difference between 1 and 4 indicates that the +3 oxidation state of the central cobalt in 1 plays a vital role in maintaining the structural integrity. A series of other Keggin-type POMs, such as K6[CoIIW12O40] (2), K5[CoIIIW12O40] (3), K6[SiCoII(H2O)W11O39] (5), and K5[PCoII(H2O)W11O39] (6), were also evaluated for their catalytic activity by comparison with 1. Our study demonstrates that the unique structural features of the mixed-valent central and peripheral cobalt atoms are essential for 1 to maintain both catalytic stability and efficiency.
274 citations
TL;DR: Electrochemical properties of the PMo-rGO catalyst were investigated in an aqueous acidic electrolyte and the hybrid catalyst showed enhanced electro-oxidation of nitrite compared with pure homogeneous PMo and rGO.
Abstract: The deposition of polyoxometalate (POM) on chemically reduced graphene oxide sheets was carried out through electron transfer interaction and electrostatic interaction between POM and graphene sheets to make a heterogeneous catalyst in aqueous media. Well dispersed individual phosphomolybdic acid (PMo) clusters were observed by electron microscopy and atomic force microscopy measurements. The interaction between polyoxometalate and the graphene sheet was confirmed by using various spectroscopic methods such as FT-IR, UV–vis, and Raman. The UV–visible, IR, and cyclic voltammetry results revealed alteration of the electronic structure of deposited PMo as a result of strong interaction with the graphene oxide surface. Electrochemical properties of the PMo-rGO catalyst were investigated in an aqueous acidic electrolyte. The hybrid catalyst showed enhanced electro-oxidation of nitrite compared with pure homogeneous PMo and rGO.
164 citations
TL;DR: In this paper, the tetrabutylammonium salt of phosphotungstic acid, TBA3PW12O40, has been encapsulated in the chromium terephthalate metal-organic framework MIL-101.
147 citations
TL;DR: Four novel polyoxometalate-based copper(I)-organic frameworks, namely, As(2)Mo(6) polyoxoanions in tetradentate modes, have been successfully synthesized under hydrothermal conditions and the photocatalytic activities of compounds 1, 3, and 4 for decomposition of methylene blue (MB) under UV light have been investigated.
Abstract: Four novel polyoxometalate-based copper(I)-organic frameworks, namely, [CuI2(cis-L1)2][CuI2(trans-L1)2Mo6O18(O3AsPh)2] (1), [CuI4(L2)4Mo6O18(O3AsPh)2] (2), [CuI4(L3)4Mo6O18(O3AsPh)2] (3), and [CuI4(L4)2Mo6O18(O3AsPh)2] (4) (L1 = 1,3-bis(1,2,4-triazol-1-yl)propane, L2 = 1,4-bis(1,2,4-triazol-1-yl)butane, L3 = 1,5-bis(1,2,4-triazol-1-yl)pentane, and L4 = 1,6-bis(1,2,4-triazol-1-yl)hexane), have been successfully synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, infrared spectra (IR), UV–vis spectra, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Compound 1 is composed of two crystallographically independent and distinct polymeric motifs: one-dimensional (1D) S-shaped chain and two-dimensional (2D) undulated layer. The S-shaped chains penetrated into the 2D parallel layers to generate an unusual 1D + 2D → three-dimensional (3D) polypseudo-rotaxane framework. In 2...
124 citations
TL;DR: In this article, the performance of the Ru-containing polyoxometalate (POM) water oxidation molecular catalyst, Rb8K2[{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2]10− (Rb8k2-1), has been studied by cyclic and rotating disk electrode voltammetric methods in aqueous media under acidic and neutral pH conditions using bare glassy carbon (GC) and graphene modified GC electrodes.
Abstract: The electrochemistry of the Ru-containing polyoxometalate (POM) water oxidation molecular catalyst, Rb8K2[{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2]10− (Rb8K2-1), has been studied by cyclic and rotating disk electrode voltammetric methods in aqueous media under acidic and neutral pH conditions using bare glassy carbon (GC) and graphene modified GC electrodes. High concentrations of supporting electrolyte are needed in neutral pH conditions to overcome the electrical double layer effect associated with the highly negatively charged 1. Complex 1 can be confined within the highly porous wet graphene film to form a stable modified electrode, which shows excellent catalytic activity and high stability toward the water oxidation reaction under neutral pH conditions, particularly in the presence of 1.0 M Ca(NO3)2. The catalytic activity of the graphene supported 1electrode is nearly two orders of magnitude higher than that reported with a polymer coated multiwalled carbon nanotube supported 1electrode when both are employed at a moderate overpotential of 0.35 V.
114 citations
TL;DR: In this paper, a series of mesoporous titania-silica-polyoxometalate (HPW-TiO2-SiO2) nanocomposite materials with different silica-titania ratios were prepared in the presence of non-ionic surfactant by evaporation induced self-assembly method.
113 citations
TL;DR: In this article, organic halides and polyoxometalates (POMs) were used as catalysts for the insertion of carbon dioxide into epoxides originating from plant oils as biogenic feedstock.
111 citations
TL;DR: In this article, the authors investigated the charge separation dynamics of photoexcited P2 to TiO2 and SnO2 in the presence of 1 and showed that the accelerated recovery of the P2 ground state bleach in the case of 1 results from ultrafast (nanosecond) electron transfer from catalyst to oxidized dye.
Abstract: Triadic photoanodes have been prepared based on nanoporous films of the metal oxides ZrO2, TiO2, and SnO2, sensitizer [Ru(bpy)2(dpbpy)]2+ (P2), and polyoxometalate water oxidation catalyst [{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2]10– (1) and investigated for their potential utility in water-splitting dye-sensitized photoelectrochemical cells. Transient visible and mid-IR absorption spectroscopic studies were carried out to investigate the charge separation dynamics of these systems, indicating that electron transfer from photoexcited P2 to TiO2 and SnO2 is still the main excited state quenching pathway in the presence of 1. Furthermore, the accelerated recovery of the P2 ground state bleach in the presence of 1 results from ultrafast (nanosecond) electron transfer from catalyst to oxidized dye. Catalyst loading appears to depend largely on the point of zero charge of the supporting oxide and as such is significantly lower on SnO2 than on TiO2: nonetheless, the rate of recovery of the ground state bleach is simila...
108 citations
TL;DR: As a heterogeneous catalyst, Co9 shows a remarkable long-term stability in turnover conditions, the oxygen evolution rate remains constant for hours without the appearance of any sign of fatigue or decomposition in a large pH range, including acidic conditions, where metal oxides are unstable.
Abstract: An insoluble salt of the water oxidation catalyst [Co9(H2O)6(OH)3(HPO4)2(PW9O34)3]16– (Co9) has been used to modify amorphous carbon paste electrodes. The catalytic activity of this polyoxometalate is maintained in the solid state. Good catalytic rates are reached at reasonable overpotentials. As a heterogeneous catalyst, Co9 shows a remarkable long-term stability in turnover conditions. The oxygen evolution rate remains constant for hours without the appearance of any sign of fatigue or decomposition in a large pH range, including acidic conditions, where metal oxides are unstable.
107 citations
TL;DR: Purely inorganic porous frameworks using catalytically active [MnV13O38](7-) clusters as nodes and rare earth ions as linkers have been successfully prepared.
TL;DR: In this paper, a tetra-manganese-containing V-centered polyoxotungstate, Na 10 [Mn 4 (H 2 O) 2 (VW 9 O 34 ) 2 ] (1 ), is proposed to reduce water using visible light irradiation (λ ǫ =455nm) with triethanolamine (TEOA) as a photosensitizer and sacrificial electron donor.
TL;DR: This combined solid state and solution study reveals in great detail the growth of a complex material from discrete monomeric building blocks.
Abstract: Understanding the aqueous state of discrete metal-oxo clusters, prenucleation clusters, and even simple ions is valuable for controlling the growth of metal-oxide materials from water. Niobium poly...
01 Jan 2013
TL;DR: The Keggin-anions being immobilized as part of the metal N-heterocyclic multi-carboxylic acid frameworks not only enhance the thermal stability of compounds 2 and 3, but also introduce functionality inside their structures, thereby, realizing four approaches in the 1D hydrophilic channel used to engender proton conductivity in MOFs for the first time.
Abstract: We have succeeded in constructing a metal-organic framework (MOF), [Cu(bpdc)(H(2)O)(2)](n) (H(2) bpdc=2,2'-bipyridyl-3,3'-dicarboxylic acid, 1), and two poly-POM-MOFs (POM=polyoxometalate), {H[Cu(Hbpdc)(H(2)O)(2)](2) [PM(12)O(40)]·nH(2)O}(n) (M=Mo for 2, W for 3), by the controllable self-assembly of H(2) bpdc, Keggin-anions, and Cu(2+) ions based on electrostatic and coordination interactions. Notably, these three compounds all crystallized in the monoclinic space group P2(1)/n, and the Hbpdc(-) and bpdc(2-) ions have the same coordination mode. Interestingly, in compounds 2 and 3, Hbpdc(-) and the Keggin-anion are covalently linked to the transition metal copper at the same time as polydentate organic ligand and as polydentate inorganic ligand, respectively. Complexes 2 and 3 represent new and rare examples of introducing the metal N-heterocyclic multi-carboxylic acid frameworks into POMs, thereby, opening a pathway for the design and the synthesis of multifunctional hybrid materials based on two building units. The Keggin-anions being immobilized as part of the metal N-heterocyclic multi-carboxylic acid frameworks not only enhance the thermal stability of compounds 2 and 3, but also introduce functionality inside their structures, thereby, realizing four approaches in the 1D hydrophilic channel used to engender proton conductivity in MOFs for the first time. Complexes 2 and 3 exhibit good proton conductivity (10(-4) to ca. 10(-3) S cm(-1)) at 100 °C in the relative humidity range 35 to about 98%.
TL;DR: A polyoxometalate-based SMM complex with single-molecule magnet behaviour was prepared, exhibiting the largest known Mn nuclearity and the most Mn valence states in the POM-basedSMM family.
TL;DR: A polyoxometalate (POM)-mediated green, facile and large-scale synthesis of 2D (2-dimensional) Ag NN/GNS nanohybrids is reported in this article.
Abstract: A polyoxometalate (POM)-mediated green, facile and large-scale synthesis of 2D (2-dimensional) Ag NN/GNS nanohybrids (where NN stands for the nanonet and GNSs for graphene nanosheets) is reported. The synthesis is convenient, rapid and environmentally friendly. The POMs serve as reducing, encapsulating and bridging molecules, and avoid introducing any organic toxic molecules. The nanohybrids have been thoroughly characterized using SEM, EDX TEM, XRD, XPS and Raman spectroscopy. Most importantly, the nanohybrids were demonstrated to act as low cost catalysts for the oxygen reduction reaction in fuel cells with similar performance to Pt catalysts. We attribute it to the high catalytic activity of the Ag NN and the excellent electron transfer properties of GNSs and also their synergistic effect, being reinforced by the presence of molybdenum species on the Ag NN/GNS surface.
TL;DR: SAXS, UV/vis, and NMR spectroscopic techniques confirm that the hybrid molecules exist as the trans dumbbell in metal-ion-free solutions and can be reversibly transformed into the cis dumbbell through coordination upon the addition of ZnCl2 into a DMSO solution containing the hybrid.
Abstract: The conformational flexibility and programmed assembly of a dumbbell-shaped polyoxometalate–organic hybrid molecule comprising two Dawson-type polyoxometalates linked by a 2,2′-bipyridine unit, which can be coordinate to metal ions, in this case of Zn2+, are described. SAXS, UV/vis, and NMR spectroscopic techniques confirm that the hybrid molecules exist as the trans dumbbell in metal-ion-free solutions and can be reversibly transformed into the cis dumbbell through coordination upon the addition of ZnCl2 into a DMSO solution containing the hybrid. Subsequent addition of EDTA reverses the switching process by extracting the Zn2+ cations from the hybrid. During the interchange process between trans and cis dumbbells, a further reorganization of the hybrid molecules occurs through bond rotation to minimize steric clashes between the polyoxometalate subunits, in order to stabilize the corresponding dumbbell conformation. The Zn2+-controlled conformational transformation of the hybrid can be further utilized ...
TL;DR: Time resolved absorption spectroscopy allows the identification of the electron transfer pathways and the determination of the time constants in covalently linked porphyrin-polyoxometalate hybrids.
Abstract: Two covalently linked porphyrin–polyoxometalate hybrids have been prepared: an Anderson-type hexamolybdate [N(C4H9)4]3[MnMo6O18{(OCH2)3CNHCO(ZnTPP)}2] with two pendant zinc(II)-tetraphenylporphyrins, and a Dawson-type vanadotungstate [N(C4H9)4]5H[P2V3W15O59{(OCH2)3CNHCO(ZnTPP)}] with one porphyrin. Electrochemical studies show independent redox processes for the organic and inorganic parts at usual potentials. Photophysical studies reveal an electron transfer from the excited porphyrin to the Dawson polyoxometalate, but not to the Anderson polyoxometalate. Time resolved absorption spectroscopy allows the identification of the electron transfer pathways and the determination of the time constants.
TL;DR: In this article, a micro reaction-controlled phase-transfer system for efficient oxidative desulfurization is presented, which provides enhanced catalytic performance for dibenzothiophene oxidation.
Abstract: A surfactant polyoxometalate compound [C16H33(CH3)(2)NOH](3){PO4[WO(O-2)(2)](4)} was encapsulated in the channels of silica to compose a micro reaction-controlled phase-transfer system for efficient oxidative desulfurization. It provides enhanced catalytic performance for dibenzothiophene oxidation. Dibenzothiophene (DBT) can be oxidized efficiently at mild conditions (atmospheric pressure, 70 degrees C, H2O2/S molar ratio is 4:1) with S-conversion near 100%. Furthermore, DBTO2 can be removed via solid phase extraction using silica gel. It provides a strategy to produce near sulfur free motor fuel. (C) 2013 Elsevier B.V. All rights reserved.
TL;DR: Managing the blues: Chiral heteropoly blues of achiral polyoxometalate clusters were created through an intermolecular interaction with a chiral organic compound.
Abstract: Managing the blues: Chiral heteropoly blues of achiral polyoxometalate clusters were created through an intermolecular interaction with a chiral organic compound Controllable chiroptical switching of the cluster complexes was possible through reversible photochromism of the polyoxometalates (see picture)
TL;DR: In this paper, the inorganic-organic hybrid compounds, namely, [Cu6Na2(Htrb)4(Mo6O19)(MoO4)6] (1), [Zn3(Htrab)(Mo10O34)]·8H2O (2), Zn2Htraβ-Mo8O26)2]·6H 2O (3), [Co2HTRb)(γ-Mo 8O26]4−4−Anion)2]-
Abstract: Five inorganic–organic hybrid compounds, namely, [Cu6Na2(Htrb)4(Mo6O19)(MoO4)6] (1), [Zn3(Htrb)(Mo10O34)]·8H2O (2), [Zn2(Htrb)(β-Mo8O26)(H2O)2]·6H2O (3), [Co2(Htrb)(β-Mo8O26)(H2O)2]·6H2O (4), and [Co2(Htrb)(γ-Mo8O26)(H2O)6]·8H2O (5), have been synthesized under hydrothermal conditions, where Htrb = hexakis(1,2,4-triazol-ylmethy1)benzene. Their structures have been determined by single-crystal X-ray diffraction analyses and characterized by infrared spectra (IR), elemental analyses and powder X-ray diffraction (PXRD) patterns. In compound 1, eight Htrb ligands bridge six Cu(II) atoms to form a metal–organic Cu6(Htrb)8 cage. Neighboring cages are further linked by the arms of the Htrb ligands to generate a fascinating 3D framework. Interestingly, each inorganic [Mo6O19]2− anion was incorporated into the Cu6(Htrb)8 cage. In 2, adjacent [Mo10O34]8− anions are linked by the bridging oxygen atoms to form 1D inorganic molybdenum oxide chains, which are extended by Zn(II) atoms into a 2D layer. Adjacent layers are further linked by the Htrb ligands in hexadentate modes to yield a 3D framework. Compounds 3 and 4 are isostructural, where the [β-Mo8O26]4− anions are bridged by the metal atoms to yield an infinite chain. The chains are further joined together by the Htrb ligands to form a 3D (4,5,6)-connected net. In compound 5, the Co(II) atoms are bridged by the Htrb ligands to generate 1D chains, which are further extended through the Mo–N bond between the Htrb ligands and the [γ-Mo8O26]4− anions into a 3D (3,4,6)-connected net. Moreover, the optical band gaps, photoluminescence, electrochemistry and the photocatalytic properties for methylene blue (MB) degradation of 1–5 have also been investigated.
TL;DR: In this paper, a supported polyoxometalate (POM), phosphotungstic acid immobilized into yttrium-doped TiO2 (HPW-Y-TiO2) nano photocatalyst was prepared via sol-gel and impregnation method.
TL;DR: Films based on electrostatic interactions between tetracationic porphyrin and Dawson type polyoxometalate are formed by the so called layer-by-layer method and their photovoltaic performances are investigated by photocurrent transient measurements which showed significant photocurrent response.
TL;DR: Kinetic studies on the hydrolysis of glycylserine and glycylglycine in the presence of the dimeric zirconium(IV)-substituted Keggin type polyoxometalate revealed that its stability is highly dependent on pH, concentration and temperature.
Abstract: Detailed kinetic studies on the hydrolysis of glycylserine (Gly-Ser) and glycylglycine (Gly-Gly) in the presence of the dimeric zirconium(IV)-substituted Keggin type polyoxometalate (Et2NH2)8[{α-PW11O39Zr(μ-OH)(H2O)}2]·7H2O (1) were performed by a combination of 1H, 13C and 31P NMR spectroscopy. The observed rate constants for the hydrolysis of Gly-Ser and Gly-Gly at pD 5.4 and 60 °C were 63.3 × 10−7 s−1 and 4.44 × 10−7 s−1 respectively, representing a significant acceleration as compared to the uncatalyzed reactions. The pD dependence of the rate constant for both reactions exhibited a bell-shaped profile with the fastest hydrolysis observed in the pD range of 5.5–6.0. Interaction of 1 with Gly-Ser and Gly-Gly via their amine nitrogen and amide oxygen was proven by 13C NMR spectroscopy. The effective hydrolysis of Gly-Ser in the presence of 1 is most likely a combination of the polarization of the amide oxygen due to its binding to the Zr(IV) ion in 1 and the intramolecular attack of the Ser hydroxyl group on the amide carbonyl carbon. The effect of temperature, inhibitors, and ionic strength on the hydrolysis rate constant was also examined. The solution structure of 1 was investigated by means of 31P NMR spectroscopy, revealing that its stability is highly dependent on pH, concentration and temperature. A 2.0 mM solution of 1 was found to be fully stable under hydrolytic conditions (pD 5.4 and 60 °C) both in the presence and in the absence of the dipeptides.
TL;DR: In this article, a polyoxometalate (POM) ionic liquid was synthesized by a precipitation/ion exchange method with choline chloride and H5PMo10V2O40 as precursors.
Abstract: A new kind of polyoxometalate (POM) ionic liquid ([(CH3)3NCH2CH2OH]5PV2Mo10O40) (abbreviated as Ch5PMo10V2O40) has been synthesized by a precipitation/ion exchange method with choline chloride and H5PMo10V2O40 as precursors. The produced salt turned out to be an original ionic liquid (IL) catalyst and exhibited a novel switchable property based on temperature variation. In this regard, it refers to a thermoregulated feature that elevated temperature leads to the miscibility of catalyst and substrate. As decreasing the temperature, the catalyst precipitates and becomes heterogeneous form to be separated automatically from the reaction mixture. The combination of POMs with choline chloride was also proved to be effective in catalyzing the oxidation of starch, which showed higher or nearly identical performance with traditional catalysts, such as FeSO4. Results demonstrated the catalyst was easily separated from the products and the retrieved Ch5PMo10V2O40 could be repeatedly used without appreciable loss of its performance, which highlighted the practical application of this important biomass.
TL;DR: A summary of the vast field of discrete polyoxometalate anions can be found in this article, where a more extensive range of polyoxoniobates with an accessible alkaline solution chemistry, polyoxoanions of d 8 metal centers, especially palladium(II), are described.
Abstract: A summary of the vast field of discrete polyoxometalate anions, which has until recently, predominantly been defined by heteropoly- and isopolymolybdates and -tungstates, and to a lesser extent, -vanadates. Unexpected developments in recent years have included the recognition of (a) a more extensive range of polyoxoniobates with an accessible alkaline solution chemistry, (b) polyoxoanions of d 8 metal centers, especially palladium(II), based on assemblies of square-planar MO 4 building units and (c) an extensive set of polyoxo(uranyl) and related actinyl clusters.
TL;DR: It can be observed from the architectures of compounds 1-5 that the secondary spacers have a great effect on the structures of the MOFs, which results in the formation of various dimensional POMOF compounds.
Abstract: To investigate the influence of a secondary spacer on the resulting structures of POMOFs containing pytz, five new compounds with different dimensionalities, [Cu5(2-pytz)6(H2O)4][SiMo12O40]·3H2O (1), [Cu3(2-pytz)4bipy][H2SiMo12O40]·bipy (2), [Cu3(2-pytz)2(bipy)4(H2O)6][H4SiW12O40]2·6H2O (3), [Cu2(2-pytz)(phen)(OH)]2[SiW12O40]·H2O (4), [Cu3(4-pytz)4(H2O)4][H2SiW12O40]·2H2O (5), were synthesized. When only 2-pytz was employed, compound 1 with a 3D framework was obtained, whereas when the secondary spacers (4,4′-bipy, phen and 4-pytz) were introduced into the reaction system of 1, compounds 2–5 were obtained and exhibit a broad range of structures, including 0D, 1D, 2D and 3D frameworks. It can be observed from the architectures of compounds 1–5 that the secondary spacers have a great effect on the structures of the MOFs, which results in the formation of various dimensional POMOF compounds. Additionally, photocatalytic experiments of 1–5 for the photocatalytic degradation of RhB under UV irradiation were also investigated.
TL;DR: In this article, a general fragmentation-and-re-assembly route was proposed to access high-nuclearity, mixed-metal polyoxometalate clusters, where reduced vanadium(IV) precursors are oxidatively disassembled into reactive fragments which subsequently reaggregate under template control in a one-pot reaction.
Abstract: We report a general fragmentation-and-re-assembly route which gives access to high-nuclearity, mixed-metal polyoxometalate clusters. Reduced vanadium(IV) precursors are oxidatively dis-assembled into reactive fragments which subsequently re-aggregate under template control in a one-pot reaction. It is shown that the oxidative dis-assembly is required, as the use of vanadium(V)-based precursors results in the formation of smaller clusters. The principle is exemplified by the synthesis of a ca. 1.8 × 1.7 × 1.0 nm3, 36-nuclear copper vanadium oxide cluster, (nBu4N)4[Cu6V30O82(NO3)2(CH3CN)6]. The cluster is characterized in the solid-state and in solution by single-crystal XRD, ESI-MS and other spectroscopic and electrochemical measurements. Several lines of evidence show that the compound is indeed formed exclusively by fully oxidized vanadium(V) centres. In addition, primary fragmentation products of the type [VO(dmso)5]2+ were isolated. The cuprovanadate cluster features pentagonal secondary building units of the type {(V)M5} (M = Cu, V) which show similar structural function as the well-known {(Mo)Mo5} pentagons observed in giant molybdate clusters. The observation suggests that more complex vanadate clusters might be accessible based on these pentagonal units.
TL;DR: In this paper, a sandwich-type polyoxometalate (Co4(H2O)2(PW9O34)2) was immobilized for the first time into the three-dimensional porous metal-organic framework, MIL-101.