Yangguang Li

Polyoxometalate-Based Nickel Clusters as Visible Light-Driven Water Oxidation Catalysts

Three new polyoxometalate(POM)-based polynuclear nickel clusters, Na24[Ni12(OH)9(CO3)3(PO4)(SiW9O34)3]·56H2O (1), Na25[Ni13(H2O)3(OH)9(PO4)4(SiW9O34)3]·50H2O (2), and Na50[Ni25(H2O)2OH)18(CO3)2(PO4)6(SiW9O34)6]·85H2O (3) were synthesized and structurally characterized. Compounds 1-3 contain {Ni12}, {Ni13} and {Ni25} core, respectively, connected by the inorganic {OH}, {PO4} and/or {CO3} linkers and encapsulated by the lacunary A-α-{SiW9O34} POM units. Compound 3 represents the currently largest POM-based Ni clusters. All three compounds contain {Ni3O3} quasi-cubane or {Ni4O4} cubane units, which are similar to the natural oxygen-evolving center {Mn4O5Ca} in photosystem II (PSII). Visible light-driven water oxidation experiments with compounds 1-3 as the homogeneous catalysts indicate that all three compounds show good photocatalytic activities. The O2 evolution amount corresponds to a high TON of 128.2 for 1, 147.6 for 2, and 204.5 for 3, respectively. Multiple experiments including dynamic light-scattering, UV-vis absorption, catalysts aged experiments, tetra-n-heptylammonium nitrate (THpANO3) toluene extraction, and capillary electrophoretic measurements results confirm that compounds 1-3 are dominant active catalysts but not Ni(2+) ions(aq) or nickel oxide under the photocatalytic conditions. The above research results indicate a new and all-inorganic polynuclear Ni-based structural model as the visible light-driven water oxidation catalysts.

An Ionothermal Synthetic Approach to Porous Polyoxometalate‐Based Metal–Organic Frameworks

Porous materials with regular, bulky, accessible cages and channels have aroused great research interest owing to their potential applications in gas storage, separation, ionexchange, and heterogeneous catalysis. 2] Polyoxometalates (POMs), as a unique class of metal oxide clusters, constitute promising building units for targeting multifunctional materials because of their nanosize, adjustable compositions, abundant topologies, and their oxygen-rich surface with strong coordination abilities. 4] Despite the unparalleled success in the preparation of microporous/mesoporous compounds by covalently linking simple metal ions and organic ligands, attempts to prepare porous POM-based metal– organic frameworks have met with only limited success. Therefore, the synthesis of such frameworks is one of the most challenging issues in synthetic chemistry. Normally, porous materials are prepared by conventional solution synthesis and hydroor solvothermal synthesis. Solvents of these systems have been largely restricted to water and traditional organic solvents, such as methanol, acetonitrile, and acetone. It is undeniable that these solvents have some intrinsic disadvantages: for example, regarding synthesis, their lower boiling points have limited the use of higher temperatures out of safety concerns; furthermore, from the environmental perspective, volatile organic solvents have caused serious health and environmental problems. Therefore, it is very necessary to explore a more effective and environmentally friendly synthetic method to overcome these existing shortcomings. Ionic liquids (ILs), composed of cations and anions, have gained attention owing to their low melting points, high ionic conductivity, non-volatility, nonflammability, high polarity, low toxicity, zero vapor pressure, and relatively low viscosity. Therefore, they may be environmentally friendly alternatives to the traditional solvents. Ionothermal synthesis, with the use of an IL as solvent and structural directing agent, has already been comprehensively discussed in several detailed reviews, and has been successfully applied in the synthesis of zeolites or microporous solids. The remarkable work of Pakhomova and others have also proved the feasibility of such ionothermal methods for preparation of non-porous POM-based materials. Inspired by these recent developments, we present herein the extension of the ionothermal method to the realm of POM-based porous frameworks and demonstrate its capacity to produce such crystalline solids. To our knowledge, no reliable design of POM-based porous materials from this approach has yet been reported to date. In planning the synthesis, we chose a readily available ionic liquid, 1-ethyl-3-methylimidazolium bromide ([Emim]Br) as solvent, the weak coordinating ability of which can facilitate the self-assembly of the polyoxoanions. Meanwhile, to surmount the major obstacle in construction of POM-based solids with extra-large pores, bulky tetrabutylammonium bromide was used. On one hand, it could increase the aperture when it acts as a counterion filling in the cavity; on the other hand, subsequent ion exchange of it with smaller cations would recover the porosity effectively. Indeed, by slightly varying the experimental conditions, three porous POM-based 3D structures have been obtained based on the above design strategy: (TBA)2[Cu (BBTZ)2(xMo8O26)] (x = b for 1, x = a for 2 and 3) (TBA = tetrabutylammonium cation, BBTZ = 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene). Single-crystal X-ray diffraction analysis reveals that the octamolybdate anion in 1 adopts the structural feature of the b-isomer, which consists of eight edge-shared MoO6 octahedra. Each [b-Mo8O26] 4 unit is covalently linked to two [CuBBTZ4] fragments through terminal oxo groups of octahedral Mo sites with Cu O distances of 2.302(4) and 2.302(4) . Each Cu cation adopts an octahedral geometry, defined by four N atoms from four BBTZ organic ligands (Cu1 N5 2.022(5), Cu1 N6 2.036(5)), and two O atoms from the [b-Mo8O26] 4 unit. The BBTZ ligands coordinated to the Cu center adopt a U-type configuration, and thus the CuBBTZ4 fragment has a windmill-type configuration with the four included angles between the four BBTZ ligands coordinated to the Cu centers of 908 (Supporting Information, Figure S1). The Cu centers of the windmills are extended to a 3D covalent net through the [b-Mo8O26] 4 units and the BBTZ ligands. The structure of 1 is very open, and contains three-directional channel systems. These channels intersect with each other and run along three different directions: 1.20 1.20 nm along the [100] direction, and 1.20 1.37 nm along the [011] and [0 11] directions, as shown in Figure 1a. From the topological view, the 3D architecture of 1 can be [*] Dr. H. Fu, Prof. C. Qin, Prof. Y. Lu, Dr. Z.-M. Zhang, Prof. Y.-G. Li, Prof. Z.-M. Su, Dr. W.-L. Li, Prof. E.-B. Wang Key Laboratory of Polyoxometalate Science of Ministry of Education Department of Chemistry, Northeast Normal University Changchun, Jilin 130024 (China) E-mail: qinc703@nenu.edu.cn wangeb889@nenu.edu.cn

Incorporating Polyoxometalates into a Porous MOF Greatly Improves Its Selective Adsorption of Cationic Dyes

Various polyoxometalates (POMs) were successfully immobilized to the mesoporous coordination polymer MIL-101 resulting in a series of POM-MOF composite materials POM@MIL-101 (POM = K4PW11VO40, H3PW12O40, K4SiW12O40). These materials were synthesized by a simple one-pot reaction of Keggin POMs, tetramethylammonium hydroxide (TMAH), terephthalic acid (H2bdc), and Cr(3+) ions. XRD, FTIR, thermogravimetric analyses (TG), inductively coupled plasma (ICP) spectrometry, and energy-dispersive X-ray spectroscopy (EDX) collectively confirmed the successful combination of POMs and the porous framework. Further, these composites POM@MIL-101 with different loading of POMs were achieved by variation of the POM dosage. Notably, the uptake capacity of MIL-101 towards organic pollutants in aqueous solution was significantly improved by immobilization of hydrophilic POMs into cages of MIL-101. An uptake capacity of 371 mg g(-1), comparable to that of the graphene oxide sponges, and much higher than that of the commercial activated carbon, was achieved at room temperature in 5 min when dipping 20 mg PW11V@MIL-101 in the methylene blue (MB) solution (100 mL of 100 mg L(-1) MB solution). Further study revealed that the POM@MIL-101 composite materials not only exhibited a fast adsorption rate towards dye molecules, but also possessed of selective adsorption ability of the cationic dyes in wastewater. For example, the adsorption efficiency of PW11V@MIL-101 (10 mg) towards MB (100 mL of 10 mg L(-1)) could reach 98 % in the initial 5 min, and it could capture MB dye molecules from the binary mixture of the MB and MO with similar size. Also, the POM@MIL-101 materials could be readily recycled and reused, and no POM leached in the dye adsorption process.

Protein-Sized Chiral Fe168 Cages with NbO-Type Topology

Protein-sized chiral Fe(168) cages with NbO-type topology were successfully prepared by the introduction of l- and d-tartrate ligands into the Fe(3+)/formate/Na(+) systems exhibiting alcohol-guest sorption properties.

A novel organic-inorganic hybrid material with fluorescent emission: [Cd(PT)(H2O)]n(PT = phthalate)

The novel organic-inorganic hybrid material [Cd(PT)(H2O)]n (1; PT = phthalate) has been hydrothermally synthesized. The X-ray diffraction study reveals that 1 exhibits an interesting two-dimensional (2D) honeycomb framework constructed from [CdO7] single helical chains linked via oxygen atoms of the PT ligands, which adopt the μ6-bridging coordination mode. A study of the physical properties of 1 demonstrates that it exhibits a strong fluorescent emission in the solid state at room temperature.

Preparation of pure nickel, cobalt, nickel–cobalt and nickel–copper alloys by hydrothermal reduction

Reduction of aqueous NiSO 4 , CoSO 4 and CuSO 4 with hydrazine has been investigated systematically to obtain ultrafine powders of pure nickel and cobalt, and of nickel–cobalt and nickel–copper alloys. The results show that the pH value and the temperature are the key factors to influence the reactions. When pH ≥ 10.0 and the temperature is higher than 85°C, pure nickel particles are obtained. Pure cobalt, and nickel–cobalt and nickel–copper alloy powders can be formed only when pH ≥ 13 and the temperature is above 120°C. The mechanism for the formation of powders of nickel and cobalt, and of nickel–cobalt and nickel–copper alloys is discussed. The XRD patterns reveal that the as-synthesized pure cobalt is the hexagonal phase (h.c.p.), the pure nickel is the cubic phase (f.c.c.) and the Co 1–x Ni x and Cu 1–x Ni x alloys are the f.c.c. phase only when the ratio of Ni to Co is above 1∶1 and Ni∶Cu is below 1∶9, respectively.

Mixed-Valent {Mn14} Aggregate Encapsulated by the Inorganic Polyoxometalate Shell: [MnIII 13MnIIO12(PO4)4(PW9O34)4]31-

The reaction of [Mn(12)(CH(3)COO)(16)(H(2)O)(4)O(12)].2CH(3)COOH.4H(2)O, Na(8)[HPW(9)O(34)].24H(2)O, K(2)HPO(4), and ethylenediamine hydrochloride in an aqueous solution leads to the isolation of a new polyoxometalate-based mixed-valent manganese aggregate, K(14)Na(17)[(Mn(III)(13)Mn(II)O(12)(PO(4))(4)(PW(9)O(34))(4)]. approximately 56H(2)O (1). Single-crystal X-ray diffraction indicates that the polyoxoanion of 1 exhibits a mixed-valent [Mn(III)(13)Mn(II)(mu(2)-O)(6)(mu(3)-O)(6)(mu(4)-PO(4))(2)(mu(5)-PO(4))(2)](5+) complex encapsulated by four [B-alpha-PW(9)O(34)](9-) trivacant Keggin-type moieties [crystal data for 1: monoclinic, C2/c (No. 15), a = 36.341(7) A, b = 18.325(4) A, c = 36.668(7) A, beta = 119.24(3) degrees, V = 21308(7) A(3), Z = 4]. In a magnetic point of view, all of these paramagnetic manganese aggregates in 1 are well wrapped into the diamagnetic inorganic shells. Variable-temperature, solid-state, direct-current susceptibility measurements show that compound 1 exhibits strong antiferromagnetic interactions inside the [Mn(14)] core.

A New Supramolecular Assembly Based on Triple-Dawson-Type Polyoxometalate and 3d-4f Heterometallic Cluster

The introduction of hexavacant Dawson-type precursor K(12)[H(2)P(2)W(12)O(48)] x 24 H(2)O into a HOAc/NaOAc (OAc(-) = acetate) buffer system containing (NH(4))(2)[Ce(IV)(NO(3))(6)] and Mn(II)(OAc)(2) x 4 H(2)O led to the isolation of a new compound, Na(20)[Ce(IV)(3)Mn(IV)(2)O(6)(OAc)(6)(H(2)O)(9)](2)[Mn(III)(2)P(2)W(16)O(60)](3) x 21 H(2)O (1). Compound 1 contains unusual triple-Dawson-type polyoxoanions [Mn(III)(2)P(2)W(16)O(60)](3)(24-) and bipyramid-like 3d-4f heterometallic clusters [Ce(IV)(3)Mn(IV)(2)O(6)(OAc)(6)(H(2)O)(9)](2+), which are arranged in a 3-D supramolecular assembly with 1-D channels. The Na(+) cations and solvent water molecules reside in the channels. Crystal data for 1 are as follows: hexagonal, P6(3)/mcm (No. 193), a = 24.959(4) A, c = 26.923(5) A, gamma = 120 degrees, V = 14525(4) A(3), and Z = 2. The electrochemical and electrocatalytic properties of compound 1 have been investigated.

Polyoxometalate-Supported 3d-4f Heterometallic Single-Molecule Magnets

The reactions of [CuTbL(Schiff)(H(2)O)(3)Cl(2)]Cl complexes with A- or B-type Anderson polyoxoanions lead to new polyoxometalate-supported 3d-4f heterometallic systems with single-molecule-magnet behavior.

N-Doped graphene-coated molybdenum carbide nanoparticles as highly efficient electrocatalysts for the hydrogen evolution reaction

In our efforts to explore promising substitutes for Pt-based electrocatalysts for the hydrogen evolution reaction (HER), a new type of molybdenum carbide nanoparticle coated with graphene shells with nitrogen dopants (abbr. MoCx@C-1) is prepared from an entangled polyoxometalate-encapsulated coordination polymer (PECP), [Zn(bimbp)2]3[PMo12O40]2·2H2O (PECP-1) (bimbp = 4,4′-bis(imidazolyl)biphenyl) via the annealing and etching processes. The synergistic effects between highly dispersive MoCx particles, graphene coatings and N dopants in MoCx@C-1 lead to remarkable HER performance in acidic media with a very positive onset potential close to that of commercial 20% Pt/C catalysts, a low Tafel slope of 56 mV dec−1, a high exchange current density of 0.27 mA cm−2, and superior long-term cycle stability. In particular, MoCx@C-1 exhibiting an overpotential of 79 mV at a current density of 10 mA cm−2 represents one of the currently best reported MoCx-based HER electrocatalysts in acidic media. Such performance is also better than that of uncoated MoCx-2 nanoparticles prepared by carburizing another PECP [Bu4N][Zn3(bimb)4Cl(MoO4)][PMoVMoVI11O40]·4H2O (PECP-2) (bimb = 1,4-bis(1-imidazolyl)benzene). This work provides a new feasible route to prepare nanostructured hybrids composed of transition metal carbides, graphene and N dopants with higher HER activity and stability.