Polyoxometalate Chemistry Research Articles

Lewis Acid Guests in a {P8W48} Archetypal Polyoxotungstate Host: Enhanced Proton Conductivity via Metal‐Oxo Cluster within Cluster Assemblies

AbstractComplexes made by hosts that completely surround their guests provide a means to stabilize reactive chemical intermediates, transfer biologically active cargo to a diseased cell, and construct molecular‐scale devices. By the virtue of inorganic host–guest self‐assembly, nucleation processes in the cavity of a {P8W48}‐archetype phosphotungstate has afforded a nanoscale 16‐AlIII‐32‐oxo cluster and its GaIII analogue that contain the largest number of AlIII/GaIII ions yet found in polyoxometalate (POM) chemistry. Interestingly, the rich Lewis acid AlIII centers within the Lewis base POM support shows an exceptional proton conductivity of 4.5×10−2 S cm−1 (85 °C, 70 % RH; RH: relative humidity), which is by far the highest conductivity reported among POM‐based single‐crystal proton conductors.

Lewis Acid Guests in a {P8 W48 } Archetypal Polyoxotungstate Host: Enhanced Proton Conductivity via Metal-Oxo Cluster within Cluster Assemblies.

Complexes made by hosts that completely surround their guests provide a means to stabilize reactive chemical intermediates, transfer biologically active cargo to a diseased cell, and construct molecular-scale devices. By the virtue of inorganic host-guest self-assembly, nucleation processes in the cavity of a {P8 W48 }-archetype phosphotungstate has afforded a nanoscale 16-AlIII -32-oxo cluster and its GaIII analogue that contain the largest number of AlIII /GaIII ions yet found in polyoxometalate (POM) chemistry. Interestingly, the rich Lewis acid AlIII centers within the Lewis base POM support shows an exceptional proton conductivity of 4.5×10-2 S cm-1 (85 °C, 70 % RH; RH: relative humidity), which is by far the highest conductivity reported among POM-based single-crystal proton conductors.

A Crown-Shaped Ru-Substituted Arsenotungstate for Selective Oxidation of Sulfides with Hydrogen Peroxide.

An acetate-bridged Ru-substituted arsenotungstate [H2 N(CH3 )2 ]14 [As4 W40 O140 {Ru2 (CH3 COO)}2 ]⋅22 H2 O (1) has been synthesized and structurally characterized. Four Ru atoms occupy the respective lacunary S2 sites of the crown-shaped polyanion [As4 W40 O140 ]28- , and each Ru atom is coordinated by one As atom and five μ2 -O atoms, comprising four from the S2 site and one from the acetate ligand. To the best of our knowledge, this coordination of the Ru atom, with an Ru-As bond length of 2.377(3)-2.387(3) Å, is unprecedented in polyoxometalate (POM) chemistry. Notably, 1 exhibits high efficiency, excellent selectivity, and good recyclability for the oxidation of sulfides with hydrogen peroxide (H2 O2 ). Catalytic oxidation of various sulfides in the presence of 1 gives superior conversion and selectivity for sulfones in acetonitrile, whereas sulfoxides are obtained in methanol.

{Nb288O768(OH)48(CO3)12}: A Macromolecular Polyoxometalate with Close to 300 Niobium Atoms

AbstractA protein‐sized (ca. 4.2×4.2×3.6 nm3) non‐biologically derived molecule {Nb288O768(OH)48(CO3)12} (Nb288) containing up to 288 niobium atoms has been obtained, which is by far the largest and the highest nuclearity polyoxoniobate (PONb). Particularly, in terms of metal nuclearity number, Nb288 is the second largest cluster so far reported in classic polyoxometalate chemistry (V, Mo, W, Nb, and Ta). Nb288 can be described as a giant windmill‐like cluster aggregate of six nanoscale high‐nuclearity PONb units {Nb47O128(OH)6(CO3)2} (Nb47) joined together by six additional Nb ions. Interestingly, the 47‐nuclearity Nb47 units generated in situ can be isolated and bridged by copper complexes to form an inorganic–organic hybrid three‐dimensional PONb framework, which exhibits effective catalytic activity for hydrolyzing nerve agent simulant of dimethyl methylphosphonate. The unique Nb47 cluster also provides a new type of topology to very limited family of Nb‐O clusters.

{Nb288 O768 (OH)48 (CO3 )12 }: A Macromolecular Polyoxometalate with Close to 300 Niobium Atoms.

A protein-sized (ca. 4.2×4.2×3.6 nm3 ) non-biologically derived molecule {Nb288 O768 (OH)48 (CO3 )12 } (Nb288 ) containing up to 288 niobium atoms has been obtained, which is by far the largest and the highest nuclearity polyoxoniobate (PONb). Particularly, in terms of metal nuclearity number, Nb288 is the second largest cluster so far reported in classic polyoxometalate chemistry (V, Mo, W, Nb, and Ta). Nb288 can be described as a giant windmill-like cluster aggregate of six nanoscale high-nuclearity PONb units {Nb47 O128 (OH)6 (CO3 )2 } (Nb47 ) joined together by six additional Nb ions. Interestingly, the 47-nuclearity Nb47 units generated in situ can be isolated and bridged by copper complexes to form an inorganic-organic hybrid three-dimensional PONb framework, which exhibits effective catalytic activity for hydrolyzing nerve agent simulant of dimethyl methylphosphonate. The unique Nb47 cluster also provides a new type of topology to very limited family of Nb-O clusters.

A gas–liquid interface synthesis in polyoxometalate chemistry: potential bag filter for volatile organic amines

Diffusion of piperidine and pyridine into an acidified aqueous solution of $$\hbox {Na}_{2}\hbox {MoO}_{4}$$ , yield compounds $$[(\hbox {pipH})_{4}][\hbox {Mo}_{8}\hbox {O}_{26}]\cdot 4\hbox {H}_{2}\hbox {O}$$ $$(\hbox {pip} = \hbox {piperidine} = \hbox {C}_{5}\hbox {H}_{11}\hbox {N})$$ (1) and $$[(\hbox {pyH})_{4}][\hbox {Mo}_{8}\hbox {O}_{26}]$$ $$(\hbox {py} = \hbox {pyridine} = \hbox {C}_{5}\hbox {H}_{5}\hbox {N})$$ (2), respectively. Compound 1 possesses supramolecular 3-D network and the relevant connectivity pattern generates channels of approximate dimensions of $$10.76 \times 11.57 \acute{{\AA }}^{2}$$ , in which the piperidinium cations are located as guests. Multidimensional supramolecular frameworks (3-D in compound 1 and 2-D layer type of network in compound 2) have been made possible, as the organic cations and polyoxometalate (POM) anions are glued together by significant hydrogen bonding interactions. The synthesis of compounds 1 and 2 provides a unique ‘gas–liquid’ synthetic route in POM chemistry that result in organic–inorganic hybrid materials with structural diversities. This synthetic approach, first time in POM chemistry, can be described as a potential bag filter for volatile organic amines. Synopsis: Diffusion of piperidine and pyridine vapours into acidified aqueous molybdate solution leads to the formation of ion pair compounds having supramolecular framework structures. These organic amines are trapped as guest or as part of the framework making the present system a potential bag filter for the volatile organic amines.

MIL-101(Cr) MOF as a Support for Reactive Polyoxometalates (POMs) Clusters. Principles of POMs Encapsulation and Chemistry of POMs Inside MIL-101 Cavities

MIL-101(Cr) MOF as a Support for Reactive Polyoxometalates (POMs) Clusters. Principles of POMs Encapsulation and Chemistry of POMs Inside MIL-101 Cavities

Synthesis and polypyrrole-loading study of antifungal medicine fluconazole functionalized Keggin polyoxotungstates

To rich the coordination polymer and polyoxometalate (POM) chemistry, two new hybrid compounds based on Keggin POMs with antifungal medicine fluconazole (Hfkz = [1-(2,4-difluorophenyl)-1,1-bis [(1H-1,2,4-triazol-1-yl)-methyl]methanol]), [Ag4(Hfkz)2][PW12O40] (AgFkzPW12) and [Ag4(Hfkz)2][SiW12O40] (AgFkzSiW12), have been successfully synthesized and structurally characterized. Moreover, to improve the photogenerated electron-hole pair separation properties, the surface of hybrid compounds was loaded by polypyrrole (PPy) through a chemical oxidation polymerization process in situ fabricating hybrid nanocomposites AgFkzPW12@PPy and AgFkzSiW12@PPy. As a result, the Hfkz molecules were successfully grafted onto the surface of the Keggin polyoxoanions, and their nanocomposites exhibit better photocatalytic activity than the respective matrix compounds under the irradiation of visible light.

Shining a light on the photo-sensitisation of organic-inorganic hybrid polyoxometalates.

Finding new ways of using visible light (or, more specifically, solar irradiation) to drive commercially significant and/or challenging chemical processes is an ongoing research goal. Polyoxometalates (POMs) are discrete, metal-oxide clusters which are cheap, robust and easily synthesised but can also act as versatile molecular building blocks, allowing for astonishing variety in their structures and properties. In particular, the rich redox chemistry and inherent photo-activity of POMs makes them attractive for use in a variety of photochemical applications, however POMs characteristically only absorb strongly in the UV region. In this perspective, we discuss the various strategies which have been employed in order to sensitise POMs to visible light, with a particular focus on hybrid inorganic-organic POM species. We will discuss the two clear photo-activation mechanisms which have been developed to date and provide an outlook on some of the possible future directions of the field.

Supramolecular chemistry of polyoxometalates: from small clusters to giant keplerates

Supramolecular chemistry of polyoxometalates: from small clusters to giant keplerates

Polioxometalatoak: Elhuyar anaien ametsak bizirik dirau!

Polioxometalatoak (POMak) kimika ez-organikoaren munduan ezagunak diren metalez eta oxigenoz osatutako kluster anionikoak dira. Azaldu ohi duten forma, konposizio eta propietate aniztasunaren ondorioz, POMek aplikazio ugari dituzte teknologiari, ekonomiari edo ingurugiroari lotutako arlo ezberdinetan. Nahiz eta aspaldidanik aplikazio katalitikoetan erabili, gaur egun etorkizunerako garrantzitsuak izango diren esparru oso ezberdinetarako ikertzen ari dira, besteak beste, hondakin-uren tratamenduan, medikuntzan, konputazio kuantikoan, energia-iturri berriztagarrietan edota sentsore kimiko lumineszenteetan. Horrengatik guztiagatik, polioxometalatoen kimika, etorkizun handiko kimika ez-organikoaren alorreko esparru dinamikoenetariko bat dela baiezta genezake.

Buildup of Redox-Responsive Hybrid from Polyoxometalate and Redox-Active Conducting Oligomer: Its Self-Assemblies with Controllable Morphologies.

A redox-responsive hybrid of polyoxometalate and conducting oligomer including its self-assemblies with controllable morphologies are reported. To this end, a hybrid molecule, containing a Lindqvist hexamolybdate as the polar head group and N,N'-bis(4'-amino-2,6-dimethylphenyl)-1,4-quinonediimine as the redox-responsive and aggregating group, is prepared. This hybrid exhibits redox-responsive behavior with controllable assembling morphological transition from spherical vesicles to short cylindrical vesicles. Besides, the hybrid-based self-assemblies are transferred to the surface, thus the surface wettability can be well-tuned owing to the morphological transitions of the self-assemblies. By marrying conducting materials with polyoxometalate chemistry, this research opens a new horizon of polyoxometalate-based self-assembled systems with potential applications in functional materials.

Syntheses, structural characterization and electrochemical properties of two rare-earth–isonicotinic-acid containing silicomolybdates

Two rare-earth–isonicotinic-acid containing silicomolybdates [NH4]6[RE(INA)2(HINA)(H2O)3]2[α-SiMo12O40]2·6H2O [RE=NdIII (1), ErIII (2); HINA=isonicotinic acid] have been synthesized in the conventional aqueous solution and characterized by elemental analyses, IR spectra, UV spectra and single-crystal X-ray diffraction. Both 1 and 2 crystallize in the triclinic P–1 space group and consist of two typical Keggin [α-SiMo12O40]4− polyanions, one isolated rare-earth-isonicotinic-acid [RE(INA)2(HINA)(H2O)3]22+ dimeric complex cation, six NH4+ ions and six lattice water molecules. Interestingly, two rare-earth ions are linked by four INA− ligands in the [Ln(INA)2(HINA)(H2O)3]22+ complex cation, which is very rare in polyoxometalate chemistry. The UV spectral measurements of 1 indicate that 1 is stable in aqueous solution in the pH range of 4.49–9.39. Furthermore, the electrochemical and electrocatalytic properties of 1 have been measured by cyclic voltammetry in 0.5mol·L−1 Na2SO4+H2SO4 aqueous solution at the scan rate of 100mV·s−1.

Ionic Complexes of Metal Oxide Clusters for Versatile Self-Assemblies

The combination of rational design of building components and suitable utilization of driving force affords spontaneous molecular assemblies with well-defined nanostructure and morphology over multiple length scales. The serious challenges in constructing assemblies with structural advantages for the realization of functions programmed into the building components usually lie ahead since the process that occurs does not always follow the expected roadmap in the absence of external intervention. Thus, prefabricated intermediates that help in governing the target self-assemblies are developed into a type of unique building blocks. Metal oxide cluster polyanions are considered as a type of molecular nanoclusters with size scale and structural morphology similar to those of many known inorganic particles and clusters but possess distinctive characteristics. Following the understanding of these clusters in self-assembly and the rationalization of their most efficient design strategy and approach, the obtained fundamental principles can also be applied in common nanoparticle- and cluster-based systems. On the other hand, the deliberate synergy offered by organic countercations that support the self-assembly of these clusters greatly expands the opportunity for the functionalization of complex building units via control of multiple interactions. The ionic combination of the inorganic clusters with hydrophilicity and the cationic organic component with hydrophobicity leads to discrete properties of the complexes. Significantly, the core-shell structure with rigid-flexible features and amphiphilicity will pave the way for hierarchical self-assemblies of the obtained complexes, while the intrinsic characteristics of the metal oxide clusters can be modulated through external physicochemical stimuli. Within this context, over the past decade we have extensively explored the ionic combination of inorganic polyanionic clusters with cationic organic amphiphiles and devoted our efforts to establishing the general rules and structure-property relationships of the formed complexes for constructing self-assemblies at the interface, in solution, and in solid matrixes. Specific interest has been focused on the functional synergy deriving from the incompatible components in highly organized self-assemblies. In this Account, we describe the recent progress on the ionic complexation of polyoxometalate clusters with cationic amphiphiles and the construction of diverse self-assembled nanostructures. First, the fundamental structural characteristics and molecular geometries of the prepared complexes are analyzed. The construction principle and diversity of the self-assembly based on the complexes and the smart stimuli response are then discussed, subject to the adjustment of various non-covalent interactions occurring in the assemblies. Subsequently, we enumerate the functional applications of the ionic complexes assembling into organic, inorganic, and even biological matrixes. The inspiration from the construction of ionic complexation and self-assembly in this Account provides vivid profiles for the design of hybrid materials involving nanoclusters and/or nanoparticles with rich potentials in addition to polyoxometalate chemistry.

Discovery of Heteropolytantalate: Synthesis and Structure of Two 6-Peroxotantalo-4-phosphate Clusters.

Polyoxometalates (POMs) of Nb and Ta are greatly different from those of Mo, W, and V that have been studied extensively and developed well. The latter can be formed simply by acidification of their aqueous monomeric oxoanions and has found application areas from catalysis to magnetism, materials science, medicine, and nanotechnology. Even now the polyoxoniobate (PONb) chemistry has accelerated dramatically over the last 15 years, and a vast expansion of available PONbs has been reported. However, after nearly 200 years of POM research, Ta-based POM chemistry is still at its infant stage and only dominated by the isopolyoxotantalate ions (Ta6 and Ta10) and transition-metal-capped Ta6 species, along with two Ti-substituted polyoxotantalates [Ti2Ta8O28]8- and [Ti12Ta6O44]10- reported very recently. In this study, we discover two novel peroxotantalophosphate clusters [P4(TaO2)6O25]12- (1) and [P4(TaO2)6O24]10- (2) by incorporating phosphorus heteroatom into Ta-oxo framework, which represent the first two examples of heteropolytantalate. Interestingly, two P2Ta3 half-units are cis- and trans-condensed in 1 and 2, leading to "open" and "closed" configurations, respectively. These two chemically and structurally related clusters can be isolated in a controlled manner, and the yields are relatively high. Both compounds were characterized in the solid state by single-crystal X-ray diffraction, 31P MAS NMR, FT-IR, TGA, and elemental analysis as well as by 31P NMR in solution. The results presented here provide a strategy to be applicable to other heteroatom-incorporated polyoxotantalates and further expand the phase space for polyoxotantalate chemistry.

Introducing Chirality into Hybrid Clusters from an Achiral Ligand: Synthesis and Characterization of Polyoxomolybdates Containing a Benzylarsonate Group

Benzylarsonic acid as a flotation collector was introduced into polyoxometalate chemistry and two new hybrid clusters, [(C6H5CH2AsO3)2Mo5O15]4– (1a) and [(C6H5CH2AsO3)4Mo12O34]4– (2a), were synthesized and characterized by chemical and spectral analysis. Self‐assembly of 1a led to chiral crystals of compound 1, whereas compound 2 was found to be a racemic mixture of the “inverted‐Keggin” hybrid cluster of 2a. Both compounds were characterized in the solid state, and their redox properties were examined.

Four-Shell Polyoxometalates Featuring High-Nuclearity Ln26 Clusters: Structural Transformations of Nanoclusters into Frameworks Triggered by Transition-Metal Ions.

A series of polyoxometalates (POMs) that incorporate the highest-nuclearity Ln clusters that have been observed in such structures to date (Ln26 , Ln=La and Ce) are described, which exhibit giant multishell configurations (Ln⊂W6 ⊂Ln26 ⊂W100 ). Their structures are remarkably different from known giant POMs that feature multiple Ln ions. In particular, the incorporated Ln-O clusters with a nuclearity of 26 are significantly larger than known high-nuclearity (≤10) Ln-O clusters in POM chemistry. Furthermore, they also contain the largest number of La and Ce centers for any POM reported to date and represent a new kind of rare giant POMs with more than 100 W atoms. Interestingly, the La26 -containing POM can undergo a single-crystal to single-crystal structural transformation in the presence of various transition-metal ions, such as Cu2+ , Co2+ , and Ni2+ , from an inorganic molecular nanocluster into an inorganic-organic hybrid extended framework that is built from POM building blocks with even higher-nuclearity La28 clusters bridged by transition-metal complexes.

Four‐Shell Polyoxometalates Featuring High‐Nuclearity Ln26 Clusters: Structural Transformations of Nanoclusters into Frameworks Triggered by Transition‐Metal Ions

AbstractA series of polyoxometalates (POMs) that incorporate the highest‐nuclearity Ln clusters that have been observed in such structures to date (Ln26 , Ln=La and Ce) are described, which exhibit giant multishell configurations (Ln⊂W6⊂Ln26⊂W100). Their structures are remarkably different from known giant POMs that feature multiple Ln ions. In particular, the incorporated Ln–O clusters with a nuclearity of 26 are significantly larger than known high‐nuclearity (≤10) Ln–O clusters in POM chemistry. Furthermore, they also contain the largest number of La and Ce centers for any POM reported to date and represent a new kind of rare giant POMs with more than 100 W atoms. Interestingly, the La26‐containing POM can undergo a single‐crystal to single‐crystal structural transformation in the presence of various transition‐metal ions, such as Cu2+, Co2+, and Ni2+, from an inorganic molecular nanocluster into an inorganic–organic hybrid extended framework that is built from POM building blocks with even higher‐nuclearity La28 clusters bridged by transition‐metal complexes.

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.

V4Mo3O14(NAr)3(μ2-NAr)3]2-: the first polyarylimido-stabilized molybdovanadate cluster.

The first molybdovanadate cluster with a polyarylimido trimetal fragment, [V4Mo3O14(NAr)3(μ2-NAr)3]2-, was in situ synthesized by using (TBA)3[H3V10O28] as proton and vanadium sources. Additional aniline hydrochlorides will give rise to the formation of phenyl guanidines, which will serve as cations and proton donors to form chain-like and dimeric supermolecules via H-bonding.