Polyoxometalate-Complexed Indium Hydroxide: Atomically Homogeneous Impregnation via Countercation Exchange.

Metal hydroxides catalyze organic transformations and photochemical processes and serve as precursors for the oxide layers of functional multicomponent devices. However, no general methods are available for the preparation of stable water-soluble complexes of metal hydroxide nanocrystals (NCs) that might be more effective in catalysis and serve as versatile precursors for the reproducible fabrication of multicomponent devices. We now report that In-substituted monodefect Wells-Dawson (WD) polyoxometalate (POM) cluster anions, [α-PWOInOH)], serve as ligands for stable, water-soluble complexes, , of platelike, predominantly cubic-phase (dzhalindite) In(OH) NCs that after optimization contain ca.

Self-Assembly and Ionic-Lattice-like Secondary Structure of a Flexible Linear Polymer of Highly Charged Inorganic Building Blocks.

Among molecular building blocks, metal oxide cluster anions and their countercations provide multiple options for the self-assembly of functional materials. Currently, however, rational design concepts are limited to electrostatic interactions with metal or organic countercations or to the attachment and subsequent reactions of functionalized organic ligands. We now demonstrate that bridging μ-oxo linkages can be used to string together a bifunctional Keggin anion building block, [PNbMoO] (), the diniobium(V) analogue of [PVMoO] ().

Ligand-Regulated Uptake of Dipolar-Aromatic Guests by Hydrophobically Assembled Suprasphere Hosts.

The selective uptake of guests by capsules, cages, and containers, and porous solid-state materials such as zeolites and metal-organic frameworks (MOFs), is generally controlled by pore size and by the dimensions and chemical properties of interior host domains. For soluble and solid-state structures, however, few options are available for modifying their outer pores to impart chemoselectivity to the uptake of similarly sized guests. We now show that by using alkane-coated gold cores as structural building units (SBUs) for the hydrophobic self-assembly of water-soluble suprasphere hosts, ligand exchange can be used to tailor the chemical properties at the pores that provide access to their interiors.

Visible-Light-Driven Water Oxidation with a Polyoxometalate-Complexed Hematite Core of 275 Iron Atoms.

Although metal oxide nanocrystals are often highly active, rapid aggregation (particularly in water) generally precludes detailed solution-state investigations of their catalytic reactions. This is equally true for visible-light-driven water oxidation with hematite α-Fe O nanocrystals, which bridge a conceptual divide between molecular complexes of iron and solid-state hematite photoanodes. We herein report that the aqueous solubility and remarkable stability of polyoxometalate (POM)-complexed hematite cores with 275 iron atoms enable investigations of visible-light-driven water oxidation at this frontier using the versatile toolbox of solution-state methods typically reserved for molecular catalysis.

Hexaniobate Cluster Anion Monolayers on Gold Nanoparticles: A New Structural Role for Alkali Metal Countercations.

Monolayer shells of polyoxotungstate cluster anions on gold nanoparticles in water were electrostatically stabilized by structurally integrated countercations, with formation constants, K, increasing in the order: Li < Na < K < TMA < Cs (TMA = tetramethylammonium). We now report that for hexaniobate cluster anions, K values increase in the same order, with the notable exception of TMA, which is effectively unable to induce monolayer formation. These findings point to a new structural model in which hexaniobate anions form a spherical coordination polymer at the gold surface with alkali metal countercations serving as single-atom structural building units between hexaniobate linkers.

Design of an inherently-stable water oxidation catalyst.

While molecular water-oxidation catalysts are remarkably rapid, oxidative and hydrolytic processes in water can convert their active transition metals to colloidal metal oxides or hydroxides that, while quite reactive, are insoluble or susceptible to precipitation. In response, we propose using oxidatively-inert ligands to harness the metal oxides themselves. This approach is demonstrated by covalently attaching entirely inorganic oxo-donor ligands (polyoxometalates) to 3-nm hematite cores, giving soluble anionic structures, highly resistant to aggregation, yet thermodynamically stable to oxidation and hydrolysis.

Polyoxometalate-Engineered Building Blocks with Gold Cores for the Self-Assembly of Responsive Water-Soluble Nanostructures.

The controlled assembly of gold nanoparticles (AuNPs) with the size of quantum dots into predictable structures is extremely challenging as it requires the quantitatively and topologically precise placement of anisotropic domains on their small, approximately spherical surfaces. We herein address this problem by using polyoxometalate leaving groups to transform 2 nm diameter gold cores into reactive building blocks with hydrophilic and hydrophobic surface domains whose relative sizes can be precisely tuned to give dimers, clusters, and larger micelle-like organizations. Using cryo-TEM imaging and H DOSY NMR spectroscopy, we then provide an unprecedented "solution-state" picture of how the micelle-like structures respond to hydrophobic guests by encapsulating them within 250 nm diameter vesicles whose walls are comprised of amphiphilic AuNP membranes.

Polyoxometalate complexes of anatase-titanium dioxide cores in water.

Polyoxometalate (POM) cluster anions are shown to serve as covalently coordinated ligands for anatase-TiO2 nanocrystals, giving isolable assemblies uniquely positioned between molecular macroanions and traditional colloidal nanoparticles. Na(+) salts of the water-soluble polyanionic structures are obtained by reacting amorphous TiO2 with the 1 nm lacunary ion, Na7 [α-XW11 O39 ] (X=P(5+) ), at 170 °C, after which an average of 55 α-PW11 O39 (7-) clusters are found as pentadentate ligands for Ti(IV) ions covalently linked to 6 nm single-crystal anatase cores. The attached POMs are reversible electron acceptors, the reduction potentials of which shift in a predictable fashion by changing the central heteroatom, X, directly influencing a model catalytic reaction.