Development of polyoxometalate-based Ag-H2biim inorganic-organic hybrid compounds functionalized for the acid electrocatalytic hydrogen evolution reaction.

The electrocatalytic hydrogen evolution reaction (HER) is an ideal method for hydrogen production. Transition metal complex electrocatalysts exhibit poor HER activity due to excessive or weak adsorption of H during the electrochemical reduction of water to molecular hydrogen in acidic environments. Developing specific functional complex materials as desired catalysts is challenging. Here, an electrochemical surface restructuring strategy of polyoxometalate (POM)-modified Ag materials toward the HER with a dramatically decreased overpotential under acidic aqueous conditions is established. We prepared two POM [SiW12O40]4- (SiW12)/[P2W18O62]6- (P2W18)-based Ag-2,2'-biimidazole (H2biim) inorganic-organic hybrid compounds (1 and 2) via the hydrothermal method and these two compounds undergo an electrochemical restructuring process in 0.5 M H2SO4 during the HER, in which Ag nanoparticles are in situ formed with the basic structures of SiW12 and P2W18 being maintained. The activated catalysts (1-AC-RDE and 2-AC-RDE) exhibit good electrocatalytic activity for the HER with good long-term stability, and the required overpotentials at a current density of 10 mA cm-2 are 112 mV (1-AC-RDE) and 91 mV (2-AC-RDE) with Tafel slopes of 77 mV dec-1 and 65 mV dec-1, respectively. The excellent electron-proton storage and transferability of SiW12 and P2W18 may provide a solution for the insufficient capture of H by Ag, leading to an effective self-optimizing behavior and superior acidic HER activity.

A huge novel polyoxometalate-based cluster Fe10P4W32 exhibiting prominent electrocatalytic activity for the oxygen evolution reaction and third-order NLO properties.

Two novel POM-based huge clusters modified by conjugated organic ligands (DAPSC), {Fe10P4W32} and {Fe8MoW18}, have been successfully isolated. Compound 1 consists of a novel huge inorganic building block {Fe10P4W32} and four organic groups DAPSC linked by ten iron ions and four sodium ions. The DAPSC ligands enhance the electric delocalization effects of polyoxoanions, leading to strengthening of the third-order nonlinear optical (NLO) responses of compounds 1-2. Additionally, the oxygen evolution reaction (OER) electrocatalytic activity and the magnetic properties of compound 1 have also been investigated.

A novel two-dimensional layered Cu2+ complex based on Dawson-like [H3BiW18O60]6-: synthesis, structure and magnetic properties.

A novel complex based on the Dawson-like [H3BiW18O60]6-, i.e. (C2H9N2)2[{Cu(C10H8N2)(C2H8N2)}2(H3BiW18O60)]·5.5H2O or (enH)2[{Cu(2,2'-bipy)(en)}2(µ4-H3BiW18O60)]·5.5H2O, (1), where enH is protonated ethane-1,2-diamine, 2,2'-bipy is 2,2'-bipyridine and en is ethane-1,2-diamine, has been synthesized hydrothermally and characterized by elemental analysis, single-crystal X-ray diffraction analysis, IR spectroscopy, powder XRD, and thermogravimetry and differential thermal analysis (TG-DTA). For (1), each [H3BiW18O60]6- anion acts as a tetradentate ligand connecting [Cu(2,2'-bipy)(en)]2+ fragments via two terminal and two bridging O atoms, forming a two-dimensional network structure. Along the a and c axes, polyoxometalate units are arranged in an AB…AB manner. The electrochemical behaviour of (1)-CPE (CPE is a carbon paste electrode) was investigated in 2 M H2SO4 solution by cyclic voltammetry (CV). The redox process of WVI/V takes place at E1/2 = -0.58 (I-I') and -0.37 V (II-II'), and at -0.04 V (III-III') for CuII/0. The magnetic properties of (1) were investigated in the range 2-300 K and indicated the existence of strong antiferromagnetic exchange interactions between the Cu2+ centres.

Three new Strandberg-type phenylphosphomolybdate supports for immobilizing horseradish peroxidase and their catalytic oxidation performances.

Three organic-inorganic hybrids containing Strandberg-type phenylphosphomolybdate anion [(C6H5PO3)2Mo5O15]4- with phenylphosphonate (PhP) centers, transition metal (TM) ions and 2,2'-biimidazole (H2biim) ligand, formulated as [(TM(H2biim)2)2(C6H5PO3)2Mo5O15]·H2O (TM = Co and Cu, abbreviated as Co-(PhP)2Mo5 and Cu-(PhP)2Mo5, respectively) and ([Ni(H2biim)3])2[(C6H5PO3)2Mo5O15]·2H2O (abbreviated as Ni-(PhP)2Mo5), were self-assembled by simple hydrothermal methods and were systematically characterized through single-crystal X-ray diffraction and other physicochemical and spectroscopic methods, which demonstrated that TM-H2biim complexes were firstly introduced into Strandberg-type organophosphomolybdate skeletons. Selecting the oxidation of cyclohexanol to cyclohexanone as a model reaction, using H2O2 as an oxidant, the catalytic oxidation activities of the Strandberg-type compounds were firstly evaluated. More importantly, these TM-(PhP)2Mo5 (TM = Co, Cu, Ni) compounds were employed to immobilize horseradish peroxidase (HRP), and showed high adsorption capacities for HRP. Laser scanning confocal microscope images showed that HRP adsorbed on the surfaces of the TM-(PhP)2Mo5 supports. Application of immobilized enzyme HRP/TM-(PhP)2Mo5 for the detection of H2O2 is also discussed.

Two New Preyssler-Type Polyoxometalate-Based Coordination Polymers and Their Application in Horseradish Peroxidase Immobilization.

Enzyme immobilization is of increasing importance for biocatalysis, for which good supports are critical. Herein, two new Preyssler-type polyoxometalate (POM)-based coordination polymers, namely, {[Cu(H2 biim)2 ][{Cu(H2 biim)2 (µ-H2 O)}2 Cu(H2 biim)(H2 O)2 ]H[({Cu(H2 biim)(H2 O)2 }0.5 )2 ((µ-C3 HN2 Cl2 ){Cu(H2 biim)}2 ){Z(H2 O)P5 W30 O110 }]⋅x H2 O}n (1: Z=Na, x=9; 2: Z=Ag, x=10; H2 biim=2,2'-biimidazole) were designed and synthesized. Compounds 1 and 2 exhibit the same skeletons, which contain multiple CuII complex fragments and penta-supported {ZP5 W30 } (Z=Na, Ag) clusters. They were first employed to immobilize horseradish peroxidase (HRP). Results show that compounds 1 and 2 are good supports for HRP immobilization, and exhibit higher enzyme loading, lower loading times, and excellent reusability. The immobilized HRP (HRP/1 or HRP/2) was further applied to detect H2 O2 , and good sensitivity, wide linear range, low detection limit, and fast response were achieved. This work shows that POM-based hybrid materials are a new kind of promising support for enzyme immobilization.

Biomolecule-mediated hydrothermal synthesis of polyoxoniobate-CdS nanohybrids with enhanced photocatalytic performance for hydrogen production and RhB degradation.

Using a biomolecule of l-cystine as the sulfur source and coordinating agent, polyoxoniobate-CdS nanohybrids were successfully synthesized under mild hydrothermal conditions. The adsorption of ammonium group (-NH2) in l-cystine molecular structure on the surface of CdS renders the amine-anchored CdS positively charged, which readily combines with the negatively charged polyoxoniobate clusters in terms of the electrostatic interaction. The as-obtained polyoxoniobate-CdS nanohybrids exhibit much superior activity for H2 evolution and RhB degradation under visible light as compared to the unhybridized CdS and polyoxoniobate. After co-loading Nb6 and NiS as cocatalyst, the H2-evolution activity of the nanohybrids is further increased up to 39 times as high as that of naked CdS, which can be attributed to an enhanced electron-transfer by adopting polyoxoniobate as electron-acceptor to retard the electron-hole recombination. The work may open an avenue for the green synthesis of cost-effective POMs-CdS nanohybrid photocatalysts for solar energy applications.

Two New Armtype Polyoxometalates Grafted on Titanium Dioxide Films: Towards Enhanced Photoelectrochemical Performance.

Two new carboxyethyltin-functionalized polyoxometalates (POMs) were successfully obtained and confirmed with physicochemical and spectroscopic methods including X-ray crystallography. The lowest unoccupied molecular orbitals of both compounds are higher in energy than that of TiO2 , and the optical band gaps of these compounds are smaller than that of TiO2 . Grafting them onto a TiO2 film created two kinds of novel photoanode materials that showed significantly enhanced photovoltaic and photocurrent responses, as well as improved photoelectrooxidation activities for methanol relative to that shown by a single TiO2 film. Further, P2 W15 -Co-SnR produced the largest photocurrent by exploring the photoelectric activities of a series of carboxyethyltin POM derivatives. This work provides new insight into the photoelectrochemical functionalization of POM-based organic-inorganic hybrids.

An open chain carboxyethyltin functionalized sandwich-type tungstophosphate based on a trivacant Dawson subunit: synthesis, characterization and properties.

A Dawson sandwich-type polyoxometalate {C(NH2)3}12H4[αßßα-{(Sn(C3H4O2))2Mn2(P2W15O56)2}]·22H2O (abbreviated as SnR-Mn-P2W15), functionalized by open chain carboxyethyltin groups, was first prepared in aqueous solution under conventional reaction conditions, and then structurally characterized by physicochemical and spectroscopic methods. Single crystal X-ray diffraction analysis revealed that two Mn(2+) cations and two [Sn(CH2CH2COO)](2+) groups are located in the internal and external positions in the so-called equatorial region of SnR-Mn-P2W15, respectively. Intriguingly, two exposed carboxyl groups act as stretching-arm brackets, which provide a favorable structure for potential further functionalization. The electrocatalytic activity of SnR-Mn-P2W15 towards the reduction of hydrogen peroxide and nitrite was studied. Additionally, its acid catalysis and oxidation catalysis activities in organic synthesis were investigated.

The kinetics and mechanism of photo-assisted Ag(I)-catalysed water oxidation with S2O8(2-).

The kinetics of photo-assisted Ag(I)-catalysed water oxidation into O2 with S2O8(2-) has been investigated. When the concentration of Ag(+) is less than 7.06 × 10(-3) mol L(-1), O2-evolution under visible light illumination (λ≥ 400 nm) obeys the first-order rate law with respect to the concentrations of Ag(+) and S2O8(2-), respectively. The rate law is expressed as -dc(S2O8(2-))/dt = 2dc(O2)/dt = kLc(S2O8(2-))c(Ag(+)), where kL is 12.4 ± 1 mol(-1) L h(-1) at 24.5 °C and the activation energy is 3.7 × 10(4) J mol(-1). It is found that visible light can improve the evolution of O2 remarkably. Compared with those without illumination, the rate constants under visible light are increased by ca. 3.8 mol(-1) L h(-1) at 4.5, 11.5, 17.5 and 24.5 °C, which are hardly affected by the reaction temperature. Employing MS/MS, ESR, XRD and UV-visible spectroscopy, the intermediate species {AgS2O8}(-), Ag(2+), OH˙, Ag2O3 and AgO(+) in the process of water oxidation have been detected. Based on the experimental evidence, the mechanism of Ag(I)-catalysed water oxidation with S2O8(2-) has been developed, in which the reaction (AgO(+) + H2O → Ag(+) + H2O2) is considered as the rate-determining step. The increase of the O2-evolution rate under visible light illumination results from the absorbance of the AgO(+) species at 375 nm, promoting the rate-determining step.

Catalytic water oxidation based on Ag(I)-substituted Keggin polyoxotungstophosphate.

A 1D chain-like Ag(I)-substituted Keggin polyoxotungstophosphate, K3[H3Ag(I)PW11O39]·12H2O, has been synthesized in a high yield and characterized by single-crystal X-ray diffraction, XRD, IR, TG/DTA and elemental analysis. When the polyoxotungstophosphate is dissolved in aqueous solutions, (31)P NMR, MS and conductivity analyses indicate that a Ag(I) anion-complex formulated as [H3Ag(I)(H2O)PW11O39](3-) is formed and is stable in a solution of pH 3.5-7.0. The oxidation of [H3Ag(I)(H2O)PW11O39](3-) by S2O8(2-) has been studied by ESR, UV-Visible spectroscopy, (31)P NMR and UV-Raman spectroscopy. It was found that [H3Ag(I)(H2O)PW11O39](3-) can be oxidized to dominantly generate a dark green Ag(II) anion-complex [H3Ag(II)(H2O)PW11O39](2-) and a small amount of Ag(III) complex [H3Ag(III)OPW11O39](3-), simultaneously evolving O2. Compared with [Ag(I)(2,2'-bpy)NO3] and AgNO3, [H3Ag(I)(H2O)PW11O39](3-) has the higher activity in chemical water oxidation. This illustrates that the [PW11O39](7-) ligand plays important roles in both the transmission of electrons and protons, and in the improvement of the redox performance of silver ions. The rate of O2 evolution is a first-order law with respect to the concentrations of [H3Ag(I)(H2O)PW11O39](3-) and S2O8(2-), respectively. A possible catalytic water oxidation mechanism of [H3Ag(I)(H2O)PW11O39](3-) is proposed, in which the [H3Ag(II)(H2O)PW11O39](2-) and [H3Ag(III)OPW11O39](3-) intermediates are determined and the rate-determining step is [H3Ag(III)OPW11O39](3-) oxidizing water into H2O2.

Two Strandberg-type organophosphomolybdates: synthesis, crystal structures and catalytic properties.

Two novel Strandberg-type organophosphomolybdate hybrid compounds [(Cu(H2O))2(µ-bipy)2(C6H5PO3)2Mo5O15]n (1) and [(Cu(H2O)2)2(µ-bipy)(C6H5PO3)2Mo5O15]n (2) (bipy = 4,4'-bipyridyl) were prepared under mild hydrothermal conditions and structurally characterized by physico-chemical and spectroscopic methods. Single crystal X-ray diffraction analysis reveals that compounds 1 and 2 are polyoxometalate-based Cu-coordination polymers with a three-dimensional framework. In 1, the Cu(2+) ions not only link [(C6H5PO3)2Mo5O15](4-) (abbreviated as {(C6H5P)2Mo5}) polyanions, but also act as connectors of bipy ligands to produce two symmetrical 1-D chains, all 1-D chains are further held together by polyanions to generate a 3-D network. In 2, each {(C6H5P)2Mo5} polyanion acting as a hexadentate ligand links four Cu(II)-bipy/H2O units, forming 2-D plane structures, which are further bridged by Cu(II)-bipy-Cu(II) fragments to generate a 3-D network. Their fluorescence properties and catalytic properties for the synthesis of cyclohexanone ethylene ketal were also investigated.

Three molybdophosphates based on Strandberg-type anions and Zn(II)-H2biim/H(2)O subunits: syntheses, structures and catalytic properties.

Three new inorganic-organic hybrid compounds based on Strandberg-type anions and Zn(ii)-H2biim/H2O subunits, namely {H4(H2biim)3}[Zn(H2biim)(H3biim)(H2O)(HP2Mo5O23)]2·3H2O (1), {H9(H2biim)7}[(µ-biim){(Zn(H2O)2)0.5(HP2Mo5O23)}2]·7H2O (2) and {H7(H2biim)7}[Zn(H2biim)(H2O)2(HP2Mo5O23)][H2P2Mo5O23]·8H2O (3) (H2biim = 2,2'-biimidazole), have been synthesized in aqueous solutions and characterized. They were also used as efficient and reusable catalysts for the protection of carbonyl compounds. Their fascinating structural features are that mono Zn(ii)-supporting biphosphopentamolybdate ({P2Mo5}) clusters exist in their crystal structures, and the nitrogen donor ligand H2biim exhibits three different coordination modes in these three compounds, respectively: for 1, two 2,2'-biimidazole molecules, as mono- and bidentate ligands coordinate to the same Zn(ii) ion; for 2, one bi-negative tetradentate ligand µ-biim bridges two Zn(ii) ions, while for 3, one neutral bidentate H2biim ligand links one Zn(ii) ion. Most importantly, compounds 1-3 represent the first example where Strandberg-type POMs are used as acid-catalysts in an organic reaction.

Polyoxometalate-based cobalt-phosphate molecular catalysts for visible light-driven water oxidation.

A series of all-inorganic, abundant-metal-based, high-nuclearity cobalt-phosphate (Co-Pi) molecular catalysts [{Co4(OH)3(PO4)}4(SiW9O34)4](32-) (1), [{Co4(OH)3(PO4)}4(GeW9O34)4](32-) (2), [{Co4(OH)3(PO4)}4(PW9O34)4](28-) (3), and [{Co4(OH)3(PO4)}4(AsW9O34)4](28-) (4) were synthesized and shown to be highly effective at photocatalytic water oxidation. The {Co16(PO4)4} cluster contains a Co4O4 cubane which is structurally analogous to the [Mn3CaO4] core of the oxygen-evolving complex (OEC) in photosystem II (PSII). Compounds 1-4 were shown to be the first POM-based Co-Pi-cluster molecular catalysts for visible light-driven water oxidation, thus serving as a functional model of the OEC in PSII. The systematic synthesis of four isostructural analogues allowed for investigating the influence of different heteroatoms in the POM ligands on the photocatalytic activities of these Co-Pi cluster WOCs. Further, the POM-based photocatalysts readily recrystallized from the photocatalytic reaction systems with the polyoxoanion structures unchanged, which together with the laser flash photolysis, dynamic light-scattering, (31)P NMR, UV-vis absorption, POM extraction, and ICP-MS analysis results collectively confirmed that compounds 1-4 maintain their structural integrity under the photocatalytic conditions. This study provides not only a valuable molecular model of the "Co-Pi" catalysts with a well-defined structure but also an unprecedented opportunity to fine-tune high-nuclearity POM clusters for visible light-driven water splitting.

Polarized micropores in a novel 3D metal-organic framework for selective adsorption properties.

A novel 3D porous metal-organic framework with 1D polarized channels was synthesized, and its adsorption properties for gas separation and chemical sensing were studied. The framework shows a preferential adsorption of CO(2) over N(2) with a selectivity of 22:1. It also exhibits a very good sensitivity to water with respect to most of the organic solvents in view of chemical sensing applications.

New tetra(organotin)-decorated boat-like polyoxometalate.

The reaction of Cl(3)Sn(CH(2))(2)COOCH(3), [H(2)P(2)W(12)O(48)](12-) and WO(4)(2-) in acetate buffer solution led to the hydrolysis of estertin into a carboxyethyltin group and the assembly of a new tetra(organotin)-decorated boat-like polyoxometalate.

A new polyoxometalate-templated Mo/V-oxide-based organic-inorganic hybrid framework with a honeycomb-like structure.

A new polyoxometalate-templated Mo/V-oxide-based organic-inorganic hybrid framework with a honeycomb-like structure has been hydrothermally synthesized and its electrocatalytic property was investigated.

Diaqua-bis(2,2'-biimidazole)cobalt(II) dichloride.

There are independent cations and four chloride anions in the crystal structure of the title complex, [Co(C(6)H(6)N(4))(2)(H(2)O)(2)]Cl(2). In each cation, the Co(II) cation is coordinated by four N atoms from two biimidazole and two O atoms of two water mol-ecules; one Co atom is at a position of site symmetry m, the other at a position of site symmetry 2/m. All Cl(-) ions and water mol-ecules are also located on the mirror plane. Each structural unit is connected through O-H⋯Cl and N-H⋯Cl inter-molecular hydrogen bonds, forming a three-dimensional supramolecular structure.

Hydrothermal synthesis and structural characterizations of two new germanates with a novel topological framework and unusual Ge4(OH)4 cubane.

Two new germanates, Ge7O12(OH)4 (C4N3H13)(0.5)(H2O)5 (1) and Ge7O12(OH)4(H2O)6 (2) have been synthesized under hydrothermal conditions and characterized by IR spectroscopy, powder XRD, TG, and single-crystal X-ray diffraction. Compound 1 crystallizes in cubic space group P3m (No. 215) with a = b = c = 7.7119(5) A, v = 458.65(5) A(3), z = 1. Compound 2: cubic, P3m, a = b = c = 7.7653(17) A, v = 457.48(17) A(3), z = 1. Both germanates keep the same topological novel inorganic framework, which is assembled from Ge4(OH)4 cubane and chiral intertwined Ge-O double helices.

Water reduction and oxidation on Pt-Ru/Y2Ta2O5N2 catalyst under visible light irradiation.

Y(2)Ta(2)O(5)N(2) is presented as a novel photocatalyst with high activity for water splitting under visible-light irradiation in the presence of appropriate sacrificial reagents; the activity for reduction to H(2) is increased by the incorporation of Pt or Ru as a co-catalyst, with a significant increase in production efficiency when both Pt and Ru are present.

Photocatalytic water reduction under visible light on a novel ZnIn2S4 catalyst synthesized by hydrothermal method.

A novel ZnIn2S4 catalyst synthesized by hydrothermal method shows high and stable photocatalytic activity for water reduction under visible light illumination.