Synthesis and characterization of a new copper-based polyoxomolybdate and its catalytic activity for azide-alkyne cycloaddition reaction under UV light irradiation

A new organic-functionalized Cu-based Anderson-type polyoxomolybdate, namely (C7H15N4)2[Na(H2O)4]2[C6H12CuMo6N2O24]·2(H2O) (CuII-POM), was synthesized via a simple one-pot reaction and subsequently characterized using a range of analytical and spectral techniques. Structural investigation by single crystal X-ray diffraction analysis revealed that the polyanion component of the synthesized compound (i.e. [C6H12CuMo6N2O24]4-) possesses a δ-isomer Anderson-type structure, which is surrounded by four lattice water molecules and four [C7H15N4-NaH15(H2O)8]4+ cations in the crystal packing arrangement. The resulting double-sided tris-functionalized Anderson-type compound can function as highly effective heterogeneous photocatalysts for the copper(I)-catalyzed Huisgen azide-alkyne cycloaddition (Cu-AAC) reaction of terminal alkyne, benzyl halides, and sodium azide (acts as the azidonation and reducing agent) in aqueous media. Ultraviolet light irradiation enhances the catalytic activity of CuII-POM ~ 4.4 times of the "off" situation under reaction conditions of 0.00239 mmol cat., 80 °C, 8 h, 2 mL H2O, So that the isolated yields for the AAC reaction involving a variety of terminal alkynes and benzyl halides using the CuII-POM catalyst ranged between 19-97%. The current study is the first report about using an efficient and economical Cu(II)-POM/UV/NaN3 catalytic system in the Cu-AAC reaction and reveals its significant potential for applying to other Cu(I)-catalyzed reactions.

Synthesis and characterization of Anderson-Evans type polyoxometalates, antibacterial properties

In the present work, the new aluminium-substituted polyoxometalates of the Anderson-Evans type have been prepared and structurally defined by the reaction of aluminium (III) chloride hexahydrate and sodium tungstate dihydrate/sodium molybdate dihydrate in an aqueous basic medium. Elemental analysis, FT-IR, TGA, 1H NMR, and 31P NMR analysis revealed that these polyoxometalates had the following formula: [Ph4P]3[Al(OH)6Mo6O18]·4H2O 1, [Ph4P]3[Al(OH)6W6O18]·4H2O 2, [C7H10N]3[Al(OH)6Mo6O18]·4H2O 3, [C7H10N]3[Al(OH)6W6O18]·4H2O 4. The compounds 1 and 2 show promising antibacterial activity against gram-positive Staphylcoccus aureus ATCC 25923 and gram-negative Escherichia coli ATCC 25922 bacteria.

Recent Advances of Anderson-Type Polyoxometalates as Catalysts Largely for Oxidative Transformations of Organic Molecules

Anderson-type ([XM₆O₂₄]ⁿ⁻) polyoxometalates (POMs) are a class of polymetallic-oxygen cluster inorganic compounds with special structures and properties. They have been paid extensive attention by researchers now, due to their chemical modification and designability, which have been widely applied in the fields of materials, catalysis and medicine. In contemporary years, the application of Anderson-type POMs in catalytic organic oxidation reaction has gradually shown great significance for the research of green catalytic process. In this paper, we investigate the application of Anderson-type POMs in organic synthesis reaction, and these works are summarized according to the different structure of POMs. This will provide a new strategy for further investigation of the catalytic application of Anderson-type POMs and the study of green catalysis.

Niobium polyoxometalate–folic acid conjugate as a hybrid drug for cancer therapeutics

In this work, covalently bonded folic acid to niobium substituted Wells-Dawson polyoxometalate, (Bu4N)5H4[P2W15Nb3O62]-folic acid, has been synthesized and characterized. Afterward, the bioactivity behavior of this hybrid compound against cervical (HeLa)...

Versatile Post-functionalisation Strategy for the Formation of Modular Organic-Inorganic Polyoxometalate Hybrids

Hybrid structures incorporating different organic and inorganic constituents are emerging as a very promising class of materials since they synergistically combine the complementary and diverse properties of the individual components. Hybrid materials based on polyoxometalate clusters (POMs) are particularly interesting due to their versatile catalytic, redox, electronic, and magnetic properties, yet the controlled incorporation of different clusters into a hybrid structure is challenging and has been scarcely reported. Herein we propose a novel and general strategy for combining multiple types of metal-oxo clusters in a single hybrid molecule. Two novel hybrid POM structures (HPOMs) bis-functionalised with dipentaerythritol (R–POM₁–R; R = (OCH₂)₃CCH₂OCH₂C(CH₂OH)) were synthesised as building-blocks for the formation of heterometallic hybrid triads (POM₂–R–POM₁–R–POM₂). Such a modular approach resulted in the formation of four novel heterometallic hybrids combing the Lindqvist {V₆}, Anderson–Evans {XMo₆} (X = Cr or Al) and trisubstituted Wells–Dawson {P₂V₃W₁₅} POM structures. Their formation was confirmed by multinuclear Nuclear Magnetic Resonance (NMR), infrared (IR) and UV-Vis spectroscopy, as well as Mass Spectrometry, Diffusion Ordered Spectroscopy (DOSY) and elemental analysis. The thermal stability of the hybrids was also examined by Thermogravimetric Analysis (TGA), which showed that the HPOM triads exhibit higher thermal stability than comparable hybrid structures containing only one type of POM. The one-pot synthesis of these novel compounds was achieved in high yields in aqueous and organic media under simple reflux conditions, without the need of any additives, and could be translated to create other hybrid materials based on a variety of metal-oxo cluster building-blocks.

A versatile modular approach has been developed for incorporating different metal-oxo nanoclusters with characteristic structures into a single hybrid molecule by covalently linking them with polyol ligands.

Solution Dynamics of Hybrid Anderson-Evans Polyoxometalates

Understanding the stability and speciation of metal-oxo clusters in solution is essential for many of their applications in different areas. In particular, hybrid organic-inorganic polyoxometalates (HPOMs) have been attracting increasing attention as they combine the complementary properties of organic ligands and metal-oxygen nanoclusters. Nevertheless, the speciation and solution behavior of HPOMs have been scarcely investigated. Hence, in this work, a series of HPOMs based on the archetypical Anderson-Evans structure, δ-[MnMo₆O₁₈{(OCH₂)₃C-R}₂]^3-, with different functional groups (R = -NH₂, -CH₃, -NHCOCH₂Cl, -N═CH(2-C₅H₄N) {pyridine; -Pyr}, and -NHCOC₉H₁₅N₂OS {biotin; -Biot}) and countercations (tetrabutylammonium {TBA}, Li, Na, and K) were synthesized, and their solution behavior was studied in detail. In aqueous solutions, decomposition of HPOMs into the free organic ligand, [MoO₄]^2-, and free Mn³⁺ was observed over time and was shown to be highly dependent on the pH, temperature, and nature of the ligand functional group but largely independent of ionic strength or the nature of the countercation. Furthermore, hydrolysis of the amide and imine bonds often present in postfunctionalized HPOMs was also observed. Hence, HPOMs were shown to exhibit highly dynamic behavior in solution, which needs to be carefully considered when designing HPOMs, particularly for biological applications.

[MW12O44] clusters: unprecedented central heteroatoms atomically dispersed in the eight coordination state bridging the 1 : 12 polyoxometalate family of Keggin and Silverton

A general synthetic protocol is developed to afford a series of [MW12O44] (M = Ni2+, Co2+ and Fe3+) clusters with diverse central heteroatoms, by employing [W12O44]16- as the structure-directing precursor. The structures of the [MW12O44] clusters are definitively confirmed by single crystal X-ray diffraction (XRD). The central heteroatoms are monodispersed and capture the "empty" cavity of [W12O44]16- with an 8 coordination number state, as demonstrated by the combination of single crystal structure extended X-ray absorption fine structure (EXAFS) fitting analysis and wavelet transform EXAFS (WTEXAFS). The chemical state of the heteroatoms is confirmed by analyses of high resolution synchrotron radiation photoelectron spectroscopy (HR-SRPES), high resolution X-ray photoelectron spectroscopy (HR-XPS) and EXAFS. The exact components of the [MW12O44] clusters and their thermal stability are also investigated by inductively coupled plasma-mass spectrometry (ICP-MS) and thermal gravimetric analyses (TGA). The powder XRD patterns indicate their phase purity. Moreover, the newly discovered [MW12O44] clusters bridge the Keggin and Silverton polyoxometalate family structures and so unify the 1 : 12 hetero-polyoxometalates.

Tris functionalized Cu-centered cyclohexamolybdate molecular armor as a bimetallic catalyst for rapid p-nitrophenol hydrogenation

An organic ligand triol protected and inorganic-ligand cyclohexamolybdate ring supported single atom Cu molecular hybrid material for rapid p-nitrophenol hydrogenation.

A Waugh type [CoMo9O32]6- cluster with atomically dispersed CoIV originates from Anderson type [CoMo6O24]3- for photocatalytic oxygen molecule activation

An atomically dispersed Waugh type [CoMo₉O₃₂]^6- cluster is obtained, employing the most flexible structure unit Anderson type [Co(OH)₆Mo₆O₁₈]^3- as a precursor. The structure of the [CoMo₉O₃₂]^6- cluster is identified by single crystal X-ray diffraction and also well characterized by FT-IR, ESI-MS, UV-Vis, EA, and TGA spectroscopy. Its 3D framework forms a quasi 2D material and possesses curved edge triangle shape nanopores with a diameter of 8.9 Å. The Co^IV and Mo^VI oxidation states and the related valence band and electronic state of Co are definitely confirmed by X-ray photoelectron spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), and bond valence sum (BVS). The [CoMo₉O₃₂]^6- cluster is a typical n-type inorganic semiconductor with a HOMO-LOMO gap of ca. 1.67 eV and exhibits reversible two-electron redox properties, evidenced by UPS, cyclic voltammetric (CV), and Mott-Schottky plot analyses. Furthermore, [CoMo₉O₃₂]^6- can effectively generate ¹O₂ under laser (365 and 532 nm) and sunlight irradiation, detected using a water-soluble DAB probe. Such an n-type multielectron reservoir semiconductor anionic [CoMo₉O₃₂]^6- cluster with thermal and electrochemical stability as an effective photosensitizer serves as a promising material in solar energy scavenging.

β-{Cr[RC(CH2O)3]2Mo6O18}3−: the first organically-functionalized β isomer of Anderson-type polyoxometalates

The first organically-functionalized butterfly-shaped β isomer of Anderson-type polyoxometalates was discovered, which will enrich polyoxometalates chemistry.

The proton-controlled synthesis of unprecedented diol functionalized Anderson-type POMs

By addition of excess acid into the reaction mixture, a series of organically-derived Anderson-type polyoxometalates, {[R1CR2(CH2O)2]CrMo6O18(OH)4}(3-), with diols as the ligands are reported herein. Such a diol functionalization mode not only works for some specific triol ligands but also can readily be extended to the diol ligands, which will greatly enrich the species of alkoxo-derivatized Anderson POM clusters.

Unprecedented χ isomers of single-side triol-functionalized Anderson polyoxometalates and their proton-controlled isomer transformation

The μ2-O atom in Anderson polyoxometalates was regioselectively activated by the introduction of protons, which, upon functionalization with triol ligands, could afford a series of unique χ isomers of the organically-derived Anderson cluster {[RCC(CH2O)3]MMo6O18(OH)3}(3-). Herein proton-controlled isomer transformation between the δ and χ isomer was observed by using the fingerprint region in the IR spectra and (13)C NMR spectra.

Novel Anderson-type [TeMo6O24]6−-based metal–organic complexes tuned by different species and their coordination modes: assembly, various architectures and properties

Four novel Anderson-type polyoxometalate [TeMo₆O₂₄]⁶⁻-based metal–organic complexes were hydrothermally synthesized and characterized, which show fluorescence, electrochemical and photocatalytic properties.

A series of Anderson-type polyoxometalate-based metal–organic complexes: their pH-dependent electrochemical behaviour, and as electrocatalysts and photocatalysts

Seven novel polyoxometalate-based metal–organic complexes are synthesized and structurally characterized, exhibiting high electrochemical sensitivity to pH and photocatalytic activities for the degradation of organic dyes under UV irradiation.

pH-tuned diverse structures and properties: two Anderson-type polyoxometalate-based metal–organic complexes for selective photocatalysis and adsorption of organic dyes

Two novel Anderson-type POM-based metal–organic complexes were synthesized, which exhibit high selective photocatalytic activities for the degradation of organic dyes. Interestingly, 2 also shows selective adsorption capacity of organic dyes.

Step-by-step strategy from achiral precursors to polyoxometalates-based chiral organic-inorganic hybrids

Using two types of triol ligands, several novel asymmetrically triol-functionalized Anderson organic hybrids have been efficiently synthesized in high purity and good yields via a convenient two-step esterification reaction. These organic-inorganic hybrids are chiral and can be spontaneously resolved with suitable solvents. Their molecular and crystal structures have been confirmed by single-crystal X-ray diffraction studies. Stable solid-state chirality of the corresponding enantiopure crystals has also been confirmed definitively by CD spectra. Interestingly, these organic-inorganic hybrids possess a layer-by-layer structure, forming solvent-accessible nanoscale chiral channels via a 1D infinite helical chain substructure. TGA measurements indicated that the species of the central heteroatoms significantly effects the stability of these compounds.

Synthesis, structure, self-assembly and genotoxicity evaluation of a series of Mn-Anderson cluster based polyoxometalate–organic hybrids

A new series of POM–organic hybrids have been developed which show less genotoxicity compared to the parent polyoxometalate cluster.