Enhanced Corrosion Resistance of Carbon Steel in Hydrochloric Acid Solution by Polyoxometalate-Estertin Derivatives.

The development of acid-resistant and efficient corrosion inhibitors is of great significance for metal protection in many industrial processes. In this work, eight cases of sandwich-type polyoxometalate (POM)-based inorganic-organic hybrids, namely, carboxyethyltin and transition metal (TM) cofunctionalized tungstoantimonates and tungstobismuthates, formulated as Na x K10-x [(SnR)2(TM(H2O)3)2(B-ß-SbW9O33)2]·mH2O and Na y K10-y [(SnR)2(TM(H2O)3)2(B-ß-BiW9O33)2]·nH2O (abbreviated as SbW9-TM-SnR and BiW9-TM-SnR; TM = Mn, Co, Ni, and Zn; m = 18, 24, 24, and 22; n = 30, 25, 20, and 21; SnR = Sn(CH2CH2COO)) are first used as green corrosion inhibitors for 20# carbon steel in 0.5-2.0 M HCl solutions. Weight loss and electrochemical experiments prove that the corrosion inhibition efficiency is all above 81% for these POM-based corrosion inhibitors at 150 mg L-1, and SbW9-Mn-SnR shows the highest efficiency of 96.9% at 150 mg L-1 after immersion in a 0.5 M HCl solution for 10 h. Scanning electron microscopy-energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses show that these POM-based inhibitors form films on the carbon steel and the adsorption mechanism obeys the Langmuir adsorption model. The thermodynamic activation parameters were calculated, proving the occurrence of both chemical and physical adsorptions. The film-forming mechanism was also analyzed. This work provides guidance for synthesizing new lacunary POM-based materials to protect metals from corrosion in HCl pickling.

A POM-based copper-coordination polymer crystal material for phenolic compound degradation by immobilizing horseradish peroxidase.

A new polyoxometalate (POM)-based organic-inorganic hybrid Cu-coordination polymer, namely {((Cu(bipy))2(µ-PhPO3)2Cu(bipy))2H(PCuW11O39)·3H2O}n (denoted as compound 1, bipy = 2,2'-bipyridine, PhPO3 = phenylphosphonate), was self-assembled hydrothermally. Single-crystal X-ray diffraction (SC-XRD) analysis shows that two unique types of 1D chains are present in compound 1, i.e. Cu(II)-organophosphine and organonitrogen complex cation ([((Cu(bipy))2(µ-PhPO3)2Cu(bipy))2]4+) chains and Cu-monosubstituted Keggin-type polyoxoanion ([PCuW11O39]5-) chains, forming a hetero-POM. Crystalline compound 1 as a new enzyme immobilization support exhibited a high horseradish peroxidase (HRP) loading capacity (268 mg g-1). The powder X-ray diffraction (PXRD), FTIR, zeta potential, confocal laser scanning microscopy (CLSM) and circular dichroism (CD) results show that HRP is only immobilized on the surface of compound 1 through simple physical adsorption without a secondary structure change. This POM-immobilized enzyme (HRP/1) was first used for degradation of pollutants in wastewater, and it showed a high degradation efficiency and TOC removal efficiency for phenol, 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) within 30 min reaction time. Moreover, HRP/1 exhibited better operational and storage stabilities and reusability compared with free HRP. This work suggests that POMs can be used as new supports for enzyme immobilization and POM-immobilized enzymes may be used as a new kind of biocatalyst for degradation of phenolic pollutants.

Two new estertin modified tungstosilicates: synthesis, catalytic activity and photoelectrochemical property.

Two new tungstosilicates (C(NH2)3)5KNa2H3[Sn(CH2CH2COOCH3)Co(H2O)2Si2W19O69]·10H2O (Si2W19-Co-SnRCOOCH3) and (C(NH2)3)5KNa2H3[Sn(CH2CH2COOCH3)Mn(H2O)2Si2W19O69]·13H2O (Si2W19-Mn-SnRCOOCH3) modified by organometal (OM) and transition metal (TM) ions were obtained, and they were self-assembled from mono-TM-containing (TM = Co, Mn) γ-[SiW10O35]6- (γ-SiW10)-based dimeric tungstosilicate and estertin Cl3SnCH2CH2COOCH3 in an acetate buffer solution, respectively. Their structures were determined with a series of physico-chemical and spectroscopic methods including X-ray crystallography, XRPD, etc. The estertin functional position in the tungstosilicate skeleton was analyzed by theoretical calculations using density functional theory (DFT). These two compounds have good catalytic activity for the oxidation of cyclohexanol to cyclohexanone. Meanwhile, they were composited with TiO2 using a facial layer-by-layer (LBL) method. The assembled composite films {Si2W19-TM-SnRCOOCH3/TiO2}n (TM = Co, Mn; n is the bilayer number, n = 1-6) exhibit efficient photoelectrocatalytic activity for the oxidation of methanol under irradiation of 100 mW cm-2 using a Xe lamp as a light source. And the {Si2W19-Co-SnRCOOCH3/TiO2}4 film produces the highest photocurrent among the composite films studied in this work. Combining the dark current measurement, surface photovoltage spectroscopy (SPV) and electrochemical impedance spectroscopy (EIS), the enhanced photoelectrocatalytic activity of {Si2W19-Co-SnRCOOCH3/TiO2}4 composite film for the oxidation of methanol is attributed to the suppressed electron-hole recombination, increased carrier separation efficiency and interfacial charge transfer.

Carboxyethyltin and transition metal co-functionalized tungstoantimonates composited with polypyrrole for enhanced electrocatalytic methanol oxidation.

Carboxyethyltin and first-row transition metals (TMs) were firstly introduced into trivacant Keggin-type tungstoantimonate in an aqueous solution, leading to the formation of four crystalline organic-inorganic hybrid sandwich-type polyoxometalates (POMs), formulated as Na10-x-yKyHx[((TM)(H2O)3)2(Sn(CH2)2COO)2(SbW9O33)2]·nH2O (SbW9-TM-SnR, TM = Mn, Co, Ni, Zn; x = 1, 1, 0, 0; y = 0, 5, 5, 2; n = 18, 24, 24, 22, respectively). SbW9-TM-SnR exhibit high catalytic ability for the oxidation of cyclohexanol. Meanwhile, SbW9-TM-SnR were composited with polypyrrole (PPy) through an electropolymerization process, forming PPy-SbW9-TM-SnR, on which platinum (Pt) was further electro-deposited to prepare PPy-SbW9-TM-SnR/Pt for electrocatalytic methanol (CH3OH) oxidation in acid solution. The composition and morphology of PPy-SbW9-TM-SnR/Pt were determined by IR, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The electrochemical experimental results show that SbW9-TM-SnR and PPy obviously enhance the electrocatalytic and anti-intoxication abilities of Pt, and the highest peak current density of 0.87 mA cm-2, corresponding to 1.85 and 1.43 times higher than those of pure Pt and PPy/Pt electrodes respectively, is acquired for the PPy-SbW9-Ni-SnR/Pt composite electrode. These findings may enlarge the application of PPy and POMs in the electrocatalytic field.

A new hexamolybdate-based copper-2,2'-biimidazole coordination polymer serving as an acid catalyst and support for enzyme immobilization.

The hydrothermal reaction of (NH4)3[CoMo6O24H6]·7H2O (CoMo6), CuCl2·2H2O and 2,2'-biimidazole (H2biim) led to the formation of a new coordination polymer, namely poly[diaquabis(2,2'-biimidazole)hexa-µ3-oxo-octa-µ2-oxo-hexaoxodicopper(II)hexamolybdate(VI)], [Cu2Mo6O20(C6H6N4)2(H2O)2]n (Cu-Mo6O20), at pH 2-3. It is obvious that in the formation of crystalline Cu-Mo6O20, the original Anderson-type skeleton of heteropolymolybdate CoMo6 was broken and the new isopolyhexamolybdate Mo6O20 unit was assembled. In Cu-Mo6O20, one Mo6O20 unit connects four [Cu(H2biim)(H2O)]2+ ions in a pentacoordinate mode via four terminal O atoms, resulting in a tetra-supported structure, and each CuII ion is shared by two adjacent Mo6O20 units. Infinite one-dimensional chains are established by linkage between two adjacent Mo6O20 units and two CuII ions, and these chains are further packed into a three-dimensional framework by hydrogen bonds, π-π interactions and electrostatic attractions. The catalytic performance of this crystalline material used as an efficient and reusable heterogeneous acid catalyst for carbonyl-group protection is discussed. In addition, Cu-Mo6O20 was applied as a new support for enzyme (horseradish peroxidase, HRP) immobilization, forming immobilized enzyme HRP/Cu-Mo6O20. HRP/Cu-Mo6O20 showed good catalytic activity and could be reused.

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.

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.

Controllable assembly, characterization and catalytic properties of a new Strandberg-type organophosphotungstate.

Using phenylphosphonic acid, simple tungstate and copper(ii) compounds as starting materials, an organic-inorganic hybrid Strandberg-type organophosphotungstate, {[(Cu(H2O)(µ-bipy))2(C6H5PO3)2W5O15]}n (bipy = 4,4'-bipyridyl) (1), was assembled successfully under hydrothermal conditions and characterized by physico-chemical and spectroscopic methods. Compound 1 represents the first example of a transition metal complex modified organophosphotungstate cluster. In the crystal structure of compound 1, the polymeric 1-D {Cu-bipy}n chains are interconnected by [(C6H5PO3)2W5O15](4-) (abbreviated as {(C6H5P)2W5}) units into a 3-D framework. A hollow Keggin isopolytungstate [H2W12O40](6-) ({W12})-Cu(ii) coordination polymer, {[Cu(bipy)2((µ-bipy)Cu(bipy))2(H2W12O40)]·12H2O}n (2), was obtained at different molar ratios of the starting materials and pH. The two Cu(ii) coordination polymers exhibit good acid-catalytic activity for the synthesis of cyclohexanone ethylene ketal. Their fluorescence properties were studied.

Enhanced Visible Photovoltaic Response of TiO2 Thin Film with an All-Inorganic Donor-Acceptor Type Polyoxometalate.

In the field of material chemistry, it is of great significance to develop abundant and sustainable materials for solar energy harvesting and management. Herein, after evaluating the energy band characteristics of 13 kinds of polyoxometalates (POMs), the trisubstituted POM compound K6H4[α-SiW9O37Co3(H2O)3]·17H2O (SiW9Co3) was first studied due to its relatively smaller band gap (2.23 eV) and higher lowest unoccupied molecular orbital (LUMO) level (-0.63 V vs NHE). Additionally, the preliminary computational modeling indicated that SiW9Co3 exhibited the donor-acceptor (D-A) structure, in which the cobalt oxygen clusters and tungsten skeletons act as the electron donor and electron acceptor, respectively. By employing SiW9Co3 to modify the TiO2 film, the visible photovoltaic and photocurrent response were both enhanced, and the light-induced photocurrent at 420 nm was improved by 7.1 times. Moreover, the highly dispersive and small sized SiW9Co3 nanoclusters loading on TiO2 were successfully achieved by fabricating the nanocomposite film of {TiO2/SiW9Co3}3 with the layer-by-layer method, which can result in the photovoltaic performance enhancement of dye-sensitized solar cells (DSSCs), of which the overall power conversion efficiency was improved by 25.6% from 6.79% to 8.53% through the synergistic effect of POMs and Ru-complex.

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.

Two carboxyethyltin functionalized polyoxometalates for assembly on carbon nanotubes as efficient counter electrode materials in dye-sensitized solar cells.

Two novel open-chain carboxyethyltin decorated sandwich-type germanotungstates have been successfully synthesized. They could markedly increase the electrocatalytic activity of single-walled carbon nanotubes toward triiodide reduction when assembled into composite electrodes, which have shown a conversion efficiency of 6.32% that is comparable to that of Pt electrodes (6.29%) when used as counter electrodes in dye-sensitized solar cells.

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.

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.

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.

[Study on spectroscopy of alpha, alpha'-dioxoketene cyclic s, s-acetals].

The rule of infrared spectroscopic characteristics of the five alpha, alpha'-dioxoketene cyclic s, s-acetals was studied, and the influence of the molecular structure on the IR was indicated. All 1H and 13C NMR chemical shifts of the five compounds were assigned, and the effects of structures on the chemical shifts of 1H and 13C NMR were discussed. The rule of change is the same as that of IR. The study offers a method of elicitation for studies on the structure and the spectroscopy of this kind of compounds.

[Study on ultraviolet spectra of alpha,alpha'-dioxoketene cyclic S,S-acetals].

The characteristics of ultraviolet spectra of five alpha,alpha'-dioxoketene cyclis,s,s-acetals (N,N-acetals) have been studied in different solvent, on the basis of last paper. And the character of ultraviolet spectra of sulfur-containing compounds and nitrogen-containing compound was compared in the same solvent, the changing rules with the change of chemical structure have been indicated. It is specially important that the character of such as this conjugated system was studied, however it almost did not do before. And the this can used in studies afterwards.