Keggin-type Polyoxoanions Research Articles

Polyoxometalate-based peroxidase-mimicking sensors for colorimetric detection and discrimination of phenolic pollutants

Phenol and its derivatives represent a kind of significant hazards to both human health and the integrity of ecological systems. Exploring an efficient detection and discrimination approach for them is urgent. Herein, a kind of polyoxometalate-based peroxidase-mimicking crystalline colorimetric sensors were developed by integrating dual active sites of Keggin-type polyoxoanions and coordination unsaturated copper centers, for which the formulas are [Cu(dppeo)3]2[Cu(dppeo)2(H2O)](dppeo)0.75[PMo12O40]2·9H2O (1), [Cu(dppeo)2(H2O)]2 [SiW12O40]·6H2O (2), [Cu(dppeo)2]3[PW12O40]2·12H2O (3), (dppeo = 1,2-bis(diphenylphosphino)ethane dioxide). Structural analysis revealed that these compounds exhibit 0-D supramolecular architecture formed through the interplay of electrostatic forces and hydrogen bonding interactions between Keggin-type polyoxoanions and dppeo-chelated copper-organic cationic fragments. Sensors 1–3 exhibit favorable peroxidase-mimicking catalytic activities, which expedite the reaction involving phenol, 4-aminoantipyrine and hydrogen peroxide (H2O2), resulting in a pronounced color change for indicating the target concentration levels. These crystalline sensors responded linearly to phenol concentration within 0.01–1.0 mM, affording low detection limits of 1.19, 1.59 and 3.78 μM for 1–3. These sensors demonstrate exceptional anti-interference capabilities and exhibit excellent applicability in real water samples, ensuring high recovery rates. By incorporating a colorimetric array with principal component analysis, the sensors effectively discriminate between common phenolic compounds. This research presents an innovative methodology for the design of crystalline sensor materials, paving the way for the detection and differentiation of phenolic pollutants within environmental applications.

N-N-Bridged Polynuclear POM-Based Coordination Polymers Based on a V-Type Ligand: Proton Conduction and Magnetism.

The construction of polyoxometalate (POM)-based coordination polymers, in the presence of a nitrogen heterocyclic ligand, is intriguing due to the potential for obtaining diverse structures. These structures exhibit extensive application possibilities in the fields of proton conductivity and magnetism. Herein, four new POM-based polynuclear coordination polymers with the formulas of {[Fe2(btb)3(H2O)2(SiW12O40)]·3H2O}n (1), {[Cd2(btb)2(H2O)6(HPMoVI10MoV2O40)]·2H2O}n (2), {[Co3(OH)2(btb)2(H2O)5(HPMoVI10MoV2O40)]·7H2O}n (3), and {[Cu3(OH)(btb)2(H2O)(HP2Mo5O23)]·6H2O}n (4) have been prepared using the V-type 1,3-bis(4H-1,2,4-triazole-4-yl)benzene (btb) ligand. Compounds 1 and 2 feature similar two-dimensional (2D) structures, derived from the binuclear Fe2N6 and Cd2N4 subunits connected by tridentate btb ligands. Meanwhile, in compound 3, hexanuclear Co6(OH)4 units are bound by quadridentate btb ligands forming a 2D layer with the same 4-c sql topology simplification as compounds 1 and 2. In compound 1, Keggin-type polyoxoanions are monodentate-coordinated to metal ions and suspended on the 2D structure, while, in compounds 2 and 3, they act as discrete counterions residing in the interstitial spaces between two adjacent layers, thereby extending the 2D structures into 3D structures through hydrogen bonding interactions. In compound 4, trinuclear Cu3(OH) subunits are further constructed into a 3D framework through cooperation with four tridentate and quadridentate btb ligands as well as Strandberg-type anions. Furthermore, the proton conduction of the four compounds has been investigated. They display high proton conductivities at 358 K and 98% RH with powdered samples, which are 1.26 × 10-3, 1.24 × 10-3, 3.24 × 10-4, and 2.57 × 10-4 S cm-1, respectively. Interestingly, by mixing with Nafion, the composite membranes of compounds 2 and 4 exhibit enhanced proton conductivities, measuring at 4.87 × 10-2 and 1.28 × 10-2 S cm-1, respectively, at 358 K and 98% RH, which suggests excellent potential for applications. In addition, compounds 1, 3, and 4 display antiferromagnetic behaviors due to similar magnetic interactions. This work can provide research insights into the assembly of 2D POM-based coordination polymers with nitrogen heterocyclic ligands and Keggin-type POMs and further promote their research progress in proton conduction.

Three-Dimensional Silver-Containing Polyoxotungstate Frameworks for Photocatalytic Aerobic Oxidation of Benzyl Alcohol.

Photocatalytic organic transformation derived by functionalized polyoxometalate (POM)-based metal-organic frameworks provides a feasible route for fine chemical synthesis. Herein, three kinds of photoactive three-dimensional silver-containing polyoxotungstate frameworks are synthesized with the formulas [Ag3L2(OH)][Na(H2O)0.5][PW12O40]·H2O (1), [Ag4L3][SiW12O40] (2), and [Ag(H2O)][Ag4L3][BW12O40]·9H2O (3) (L = 1,4-di(4H-1,2,4-triazol-4-yl)benzene). In compounds 1-3, the cationic Ag-triazole clusters with diverse nuclei serve as nodes to assemble with rigid bridging ligands (L) and polyoxoanions to extend into stable three-dimensional frameworks, in which Keggin-type anions act as guests or pendants. When using them as heterogeneous photocatalysts, compounds 1-3 show high catalytic activity and selectivity for the photocatalytic aerobic oxidation of benzyl alcohol to benzoic acid under 10 W 365 nm light irradiation. Among them, compound 1 exhibits the highest performance with ca. 99% benzyl alcohol conversion and 99% selectivity of benzoic acid in 9 h. Compounds 2 and 3 show ca. 79 and 88% conversions of benzyl alcohol, respectively, which are higher than those of the individual Keggin-type precursors. Moreover, mechanism investigation suggests that the synergistic cooperation occurring between cationic Ag-triazole clusters and Keggin-type polyoxoanions modulates the energy band structures of compounds 1-3, resulting in the efficient separation of photogenerated carriers and accelerating the aerobic oxidation of benzyl alcohol. This work provides some important guidance for the design and development of efficient POM-based photocatalysts for practical organic transformation.

A Lacunary Polyoxometalate Anion Tightly Sealed in a ZIF‐8 Polyhedron with Ultrafast Cationic Dye Adsorption

AbstractFinding efficient materials for treatment of dye wastewater is a hot research topic in the field of environmental science. In this paper, the mono‐lacunary polyoxometalate anion (SiW11) is completely sealed in a zeolitic imidazolate (ZIF‐8) polyhedron, forming a new polyhedral absorbent, SiW11@ZIF‐8, with an intact surface and a negative charge center. Unlike saturated Keggin type polyoxoanions, SiW11is only stable under neutral conditions and does not release any protons in solutions. Therefore, SiW11@ZIF‐8 does not display the usually observed acid‐induced etching and shows effective and ultrafast adsorption for the cationic dye methylene blue. This work not only indicates that the neutral polyoxoanion is a more suitable candidate to be sealed in ZIF‐8 to form a stable unpunched composite, but also provides a new concept for the design of stable polyoxometalate@ZIF adsorbents to be potentially used in the treatment of cationic dyes in wastewater.

Tetrabutyl Ammonium Salts of Keggin-Type Vanadium-Substituted Phosphomolybdates and Phosphotungstates for Selective Aerobic Catalytic Oxidation of Benzyl Alcohol

A series of tetrabutyl ammonium (TBA) salts of V-included Keggin-type polyoxoanions with W (TBA4PW11V1O40 and TBA5PW10V2O40) and Mo (TBA4PMo11V1O40 and TBA5PMo10V2O40) as addenda atoms were prepared using a hydrothermal method. These synthesized materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-Vis diffuse reflectance (DRS UV-Vis), thermogravimetric analysis (TGA), CHN elemental analysis (EA), inductively coupled plasma spectrometry (ICP-MS), and N2 physisorption techniques to assess their physicochemical/textural properties and correlate them with their catalytic performances. According to FT-IR and DRS UV-Vis, (PVXW(Mo)12−XO40)(3+X)− anions are the main species present in the TBA salts. Additionally, CHN-EA and ICP-MS revealed that the desired stoichiometry was obtained. Their catalytic activities in the liquid-phase aerobic oxidation of benzyl alcohol to benzaldehyde were studied at 5 bar of O2 at 170 °C. Independently of the addenda atom nature, the catalytic activity increased with the number of V in the Keggin anion structure. For both series of catalysts, TBA salts of polyoxometalates with the highest V-substitution degree (TBA5PMo10V2O40 and TBA5PW10V2O40) showed higher activity. The maximum benzyl alcohol conversions obtained were 93% and 97% using (TBA)5PMo10V2O40 and (TBA)5PW10V2O40 as catalysts, respectively. In all the cases, the selectivity toward benzaldehyde was higher than 99%.

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.

Three polyoxometalate-tuned copper complexes based on in situ ligand transformation: syntheses, structures, and properties

Depending on the in situ ligand transformation of 3,5-di(1,2,4-triazol-1-yl)benzonitrile (DTCN) to 3,5-di(1,2,4-triazol-1-yl)benzoic acid (DTCA) under hydrothermal condition, three polyoxometalate-based copper complexes, [CuI 4CuII 2(OH)2(H2O)4(DTCA)4(HPMoVI 10MoV 2O39)] (1), [Cu4(OH)2(H2O)4(DTCA)2(SiW12O40)]·11H2O (2), and {Cu2Cl(H2O)(HDTCA)2[CrMo6(OH)6O18)]}·4H2O (3), have been isolated through changing the polyoxoanions. Introducing Keggin-type polyoxoanions [PMo12O40]3− or [SiW12O40]4− to reaction systems, both 1 and 2 display 3-D framework structures containing Cu/DTCA metal-organic belts, and a kind of poly-Keggin chain derived from [PMo12O40]3− polyoxoanions exist in 1. When the Anderson-type polyoxoanion [CrMo6(OH)6O18)]3− is utilized, a 2-D grid-like layer resulted in 3, in which the DTCA ligands are embedded, revealing that the polyoxoanions have key roles in regulating the structures of complexes. The investigations on electrochemical properties and photocatalytic activities for the degradation of organic dyes of 1–3 have been carried out.

Multidimensional CuII incorporated POMs [KI2CuII(en)2(β-Mo8O26)]n and [KI2CuII3(H2O)10(W12O40)0.2(H2O)]n: Syntheses, structures and catalytic epoxidation

Two CuII incorporated polyoxometalate compounds, [KI2CuII(en)2(β-Mo8O26)]n (1) and [KI2CuII3(H2O)10(W12O40)·2(H2O)]n (2), have been synthesized and structurally characterized. In complex 1, the Mo8O264− anion shows an archetypal β-type octamolybdate that contains eight {MoO6} subunits which are further attached by a KIO8 unit to present a 1D chain. Consecutive 1D layers are connected by a mononuclear [Cu(en)2O2]2+ subunit to generate a 2D framework in the crystallographic ab plane. In complex 2, the W12O408− anion is a typical Keggin-type polyoxo anion containing twelve {WO6} octahedra which are alternately coordinated to KIO4 tetrahedra to generate a 1D chain. These 1D layers are interconnected by [Cu(H2O)]2+ synchronously to form a 2D framework in the crystallographic ac plane. Catalytic activity studies of complex 1 gave 91% styrene conversion with 72% epoxide selectivity and 85% cyclohexene conversion with 65% epoxide selectivity and those for complex 2 showed 88% styrene conversion with 70% epoxide selectivity and 81% cyclohexene conversion with 63% epoxide selectivity.

Fabrication and Electrochemical Performance of Polyoxometalate-Based Three-Dimensional Metal Organic Frameworks Containing Carbene Nanocages.

Two new polyoxometalate (POM)-based three-dimensional metal organic carbene frameworks, [Ag10(trz)4(H2O)2][HPW12O40] (POMs@MCNCs-1) and [Ag10(trz)4(H2O)6][H2SiW12O40] (POMs@MCNCs-2), were hydrothermally synthesized, in which Keggin-type polyoxoanions as templates induce the formation of two different kinds of metal-carbene nanocages (MCNCs) for the first time. Combination of the reversible multielectron redox behavior and electron storage functions of POMs with the good electrical conductivity of the single-walled carbon nanotubes (SWNTs) renders the POMs@MCNCs-1/SWNT composite excellent electrochemical performance and good stability as anode materials of lithium-ion batteries, with up to 2000 mA h g-1 for the first discharge capacity and ca. 859 mA h g-1 for the second cycle at a current density of 100 mA g-1. The successful fabrication of unprecedented MCNCs into the POM-based three-dimensional metal-organic frameworks in the present work must initiate extensive research interests in diverse fields.

Self-assembly study of nanometric spheres from polyoxometalate-phenylalanine hybrids, an experimental and theoretical approach.

Herein, we report on the study of supramolecular assemblies based on polyoxometalates (POMs) upon their modification with amino acids. Two POM-amino acid hybrids were synthesized by coupling a functionalized Keggin type polyoxoanion [PW11O39{Sn(C6H4)C[triple bond, length as m-dash]C(C6H4)COOH}]4- with carboxyl-protected (methyl-ester) phenylalanine or diphenylalanine peptides. Surprisingly, all compounds, including the initial POM, formed supramolecular nanospheres in different solvent mixtures, which were examined by scanning electron microscopy (SEM). Molecular dynamics (MD) simulations for the POM-amino acid species revealed that the hydrophobic forces are mainly responsible for the initial aggregation into incipient micelle type structures, in which the organic arms are buried inside the aggregate while POM polar heads are more exposed to the solvent with tetrabutyl-ammonium counter cations acting as linkers.

Two hybrids based on Keggin polyoxometalates and dinuclear copper(II) complexes: syntheses, structures and electrocatalytic properties

By introducing mixed-ligands en and ox, $$\hbox {Cu}^{2+}$$ and different polyoxotungstates as synthons, two new polyoxotungstate-based inorganic-organic hybrid compounds $$\{[\hbox {Cu}_{2}\hbox {(en)}_{2}\hbox {(ox)}]\hbox {[HPW}_{12}\hbox {O}_{40}]\}\cdot \hbox {(en)}_{2}\cdot \hbox {2H}_{2}\hbox {O}$$ (1) and $$\{[\hbox {Cu}_{2}\hbox {(en)}_{2}\hbox {(ox)}]$$ [ $$\hbox {H}_{3}\hbox {BW}_{12}\hbox {O}_{40}]\}\cdot \hbox {(en)}_{2}\cdot \hbox {2H}_{2}\hbox {O}$$ (2) (en = ethylenediamine and ox = oxalate), were obtained in identical hydrothermal conditions and further characterized by elemental analyses, IR spectroscopy and single-crystal X-ray diffraction. Structural analyses revealed that both compounds are isostructural, and show one-dimensional (1D) chain constructed by $$\hbox {[XW}_{12}\hbox {O}_{40}]^{\mathrm{n}-}$$ (X = P 1, B 2) Keggin-type polyoxoanions and $$[\hbox {Cu}_{2}\hbox {(en)}_{2}\hbox {(ox)}]^{2+}$$ dinuclear copper subunits. The electrochemical experiments indicated that 1-based carbon paste electrode possesses high catalytic efficiency and selectivity towards reduction of $$\hbox {H}_{2}\hbox {O}_{2}$$ , and thus 1 has potential to detect $$\hbox {H}_{2}\hbox {O}_{2}$$ . SYNOPSIS Two new hybrids based on polyoxoanions and dinuclear copper complexes have been synthesized and characterized. The results of electrocatalytic experiments indicate that the hybrid-based electrode possesses high catalytic efficiency and selectivity towards reduction of $$\hbox {H}_{2}\hbox {O}_{2}$$ .

Tuning of the photocatalytic performance of g-C3N4 by polyoxometalates under visible light.

Carbon nitride (g-C3N4), as a rising star of metal-free photocatalysts, has received considerable attention. However, for practical application, the photocatalytic efficiency of g-C3N4 remains to be further improved. Herein, a series of Keggin-type polyoxoanion (polyoxoanions = SiW12O404-, PW12O403-, PMo12O403-) modified g-C3N4 (POM/C3N4) composites have been successfully prepared. The results of XRD, TEM, XPS and EDAX reveal that a small amount of polyoxoanions was modified on the surface of g-C3N4 with electrostatic and hydrogen bonding interactions. Photocatalytic experiments indicate that these composites exhibit enhanced methyl orange (MO) degradation photocatalytic activity and water splitting H2 production under visible light irradiation. The loading amount and the type of polyoxoanion can tune the photocatalytic performance of the composites. Among these catalysts, 5% SiW12O404- (SiW12)-modified g-C3N4 has the best photocatalytic performance, which is 4.4 times higher than that of pure g-C3N4 for the degradation of MO. The photocatalytic mechanism reveals that polyoxoanions can act as electron traps, which can efficiently promote the separation of photogenerated electrons and holes of C3N4, thus resulting in the enhanced photocatalytic performance of the composites.

Two multifunctional organic-inorganic hybrid complexes based on polyoxometalates, BiEDTA and sodium linker: crystal structures, photochromic, and catalytic performances

Two 3-D organic–inorganic hybrid supermolecular complexes, Na(BiHEDTA·2H2O)3(PW12O40)·2H3O (BiPW) and Na(BiHEDTA·2H2O)3(PMo12O40)·2H3O·2H2O (BiPMo) ethylenediamine tetraacetic acid (EDTA) have been synthesized by solution method and characterized by ultraviolet visible (UV–vis) spectroscopy, thermogravimetric-differential thermal analysis, photoluminescence, cyclic voltammetry, and single-crystal X-ray diffraction (XRD). XRD analysis reveals that BiPW and BiPMo are isostructural with 3-D architectures assembled by 2-D layer tetranuclear cation and a Keggin-type polyoxoanion. Although these two hybrids exhibit similar structures, the properties depend on the nature of polyoxoanion [PM12O40]3− (M = W, Mo). Under UV irradiation, BiPW and BiPMo show fast response of reversible and irreversible photochromism, respectively. BiPW exhibits excellent photocatalytic activity in degradation of methyl orange dyes under irradiation of UV–visible light. It can be reused for at least six cycles without obvious loss of activity in the degradation experiments; BiPMo shows catalytic activity in elimination of methanol. The elimination rate of methanol reaches 56.9% when the concentration of methanol is 2.3 g·m−3 and the flow velocity is 10 mL·min−1 at 100 °C.

Immobilization of Polyoxometalate in the Metal-Organic Framework rht-MOF-1: Towards a Highly Effective Heterogeneous Catalyst and Dye Scavenger.

A series of three remarkable complexes [PMo12O40]@[Cu6O(TZI)3(H2O)9]4·OH·31H2O (H3TZI = 5-tetrazolylisophthalic acid; denoted as HLJU-1, HLJU = Heilongjiang University), [SiMo12O40]@[Cu6O(TZI)3(H2O)9]4·32H2O (denoted as HLJU-2), and [PW12O40]@[Cu6O(TZI)3(H2O)6]4·OH·31H2O (denoted as HLJU-3) have been isolated by using simple one-step solvothermal reaction of copper chloride, 5-tetrazolylisophthalic acid (H3TZI), and various Keggin-type polyoxometalates (POMs), respectively. Crystal analysis of HLJU 1−3 reveals that Keggin-type polyoxoanions have been fitted snuggly in the cages of rht-MOF-1 (MOF: metal−organic framework) with large cell volume in a range of 87968−88800 Å3 and large pore volume of about 68%. HLJU 1–3 exhibit unique catalytic selectivity and reactivity in the oxidation of alkylbenzene with environmental benign oxidant under mild condition in aqueous phase as well as the uptake capacity towards organic pollutants in aqueous solution.

Synthesis and photocatalytic hydrogen evolution activity of three Keggin-type polyoxometalates with different central atoms

A series of new complexes based on Keggin-type polyoxoanions (HTEA)2{[Na(TEA)2]H[SiW12O40]}∙5H2O (1), (HTEA)2{[Na(TEA)2][PW12O40]}∙4H2O (2) and (HTEA)2{[Na(TEA)2]H[GeW12O40]}∙4H2O (3) (TEA=triethanolamine) have been designed and synthesized. Single-crystal X-ray diffraction analyses reveal that compounds 1, 2 and 3 are isostructural, which exhibit the 1D chain structures consisting of Keggin-type polyoxoanions and {Na(TEA)2} linkers. Their structures were further characterized by XRD, IR spectroscopy, UV spectroscopy, elemental analyses, and thermogravimetric analysis. Moreover, compounds 1–3 present good the photocatalytic hydrogen evolution activities, which may be ascribed to the introduction of the sacrificial electron donors TEA to their structures, further, their photocatalytic hydrogen evolution activities are compared with its homologous Keggin-type heteropolyacid to verify the effect of TEA.

Synthesis and Characterization of First 3-D Inorganic–Organic Hybrids Based on Keggin Polyoxometalate and Melamine with Three Layers Solvent Diffusion Method

Two new organic–inorganic Keggin-based hybrids, namely, (MELH2)1.5(MELH)2 (AcNit)[PMo12O40]·2H2O (1) and (MELH)2(H3O)[PMo12O40]·8H2O (2), (MELH2 = C3N6H8 2+, MELH = C3N6H7 + and AcNit = CH3CN) were synthesized in room temperature and characterized by elemental analysis, Fourier transform infrared and UV spectroscopes and single crystal X-ray diffraction. The X-ray diffraction analysis show that the complex 1 constructed from Keggin polyoxoanions and melamine (MEL) cations, exhibits an extended three-dimensional (3D) supramolecular network via hydrogen bond and π–π stack interactions. Compound 2 presents an intriguing double Keggin-anion template 3D structure, made up of [PMo12O40]3− Keggin type polyoxoanions linked with MEL cations through van der Waals interactions. Crystal structure analysis reveals that these are the first Keggin polyoxoanion supported MEL cations.

Polyoxometalate-based layered nano-tubular arrays: facile fabrication and superior performance for catalysis

Keggin-type polyoxoanion PW12O403−-containing one-dimensional nano-tubular arrays fabricated within porous templates show a superior performance just through simple filtrating processes.

A novel 2D supramolecular compound of zwitterion and polyoxoanion and its application in catalytic desulfurization

A novel 2D supramolecular compound based on the flexible zwitterion and Keggin-type polyoxoanion, formulated [C8H11N2O4]3PMo12O40·2CH3OH·H2O (compound 1) has been synthesized from the reaction mixture of 12-molybdophosphoric acid and the N,N′-diacetic acid imidazolium chloride under room temperature. Compound 1 crystallizes in the P2(1)/n space group of monoclinic system with a=13.1231(7), b=26.5393(14), c=20.0457(11)Å, α=13.1231(7), V=6833.7(6)Å3, C26H43Mo12N6O55P, Mr=2501.91, Dcalc=2.432mg/m3, μ=2.262mm−1, F(000)=4800, Z=4, R1=0.0522 and wR2=0.1242. X-ray crystallography shows that, under catalysis of the polyoxometalate anion, one of the carboxyl groups in each zwitterionic molecule is esterified by methanol solvent. The polyoxometalate anions extend to a honeycomb-like inorganic layer via short contact interactions of O⋯O. Compound 1 is employed as a catalytic oxidant to reveal its desulfurization behavior. The result shows that the supramolecular compound exhibits attractive photochromism. In addition, compound 1 retains Keggin molybdate anion’s desulfurization activities with 30mg compound at 313K for 15min.

Synthesis, Crystal Structure, and Magnetic Property of an Organic–Inorganic Hybrid Silicotungstate With Supporting Dinuclear Copper Complexes

A new organic–inorganic hybrid silicotungstate [Cu2(phen)2Cl(H2O)(OH)]2[α-SiW12O40]·8 H2O (1) (phen = 1,10-phenanthroline) with supporting dinuclear copper complexes has been hydrothermally synthesized and structurally characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction. The molecular unit of 1 consists of two pendant coordination cations [Cu2(phen)2Cl(H2O)(OH)]2+ and one saturated Keggin-type silicotungstate polyoxoanion [α-SiW12O40]4− and eight lattice water molecules. The most intriguing feature is that each bi-copper cation [Cu2(phen)2(μ2-Cl)(H2O)(OH)]2+ is constructed from two [Cu(phen)]2+ cations linked by one μ2-Cl and one hydroxyl bridges. Magnetic measurements indicate that 1 demonstrates the ferromagnetic exchange interactions within CuII centers.

PH-dependent assembly of two polyoxometalate host-guest structural isomers based on Keggin polyoxoanion templates.

Two interesting polyoxometalate-templated host–guest compounds 1 and 2 with the same chemical formulae of [Ag6(tpt)4(SiW12O40)Cl2]·2H2O have been obtained by hydrothermal reactions of monolacunary Keggin-type K8[α-SiW11O39]·13H2O with CH3COOAg and tpt ligands under different pH conditions. Compounds 1 and 2 are structural isomers. In 1, the novel chair-like tetranuclear [Ag4(μ3-Cl)2]2+ clusters and additional Ag+ ions are linked by tpt ligands to form a 2D double-layered structure featured with two different types of voids in the layer, and the double-layers are stacked into a 3D host supramolecular framework with 1D channels filled with Keggin [SiW12O40]4− polyoxoanions and water molecules as guests. In 2, Ag+ ions are linked by tpt ligands into a 3D framework of 10(3)-ths topology. The most outstanding structural feature of 2 is that upon six-fold interpenetration among 10(3)-ths nets there are still nanosized channels along the a axis to accommodate Keggin polyoxoanions and water molecules as guests. Compound 2 represents the first example of six-fold interpenetrating cationic networks templated with polyoxoanions. In this work, the obvious differences in structure between 1 and 2 show that hydrochloric acid solution conditions, which offer not only H+ to regulate the pH value but also Cl− to coordinate with Ag+ ions, play an important role in the formation of host frameworks templated by Keggin-type polyoxoanions. The photoluminescence properties of 1 and 2 have been investigated in the solid state.