Cyclodextrin-Assisted Hierarchical Aggregation of Dawson-type Polyoxometalate in the Presence of {Re6Se8} Based Clusters

International audienceThe association of metallic clusters (CLUS) and polyoxometalates (POM) into hierarchical architectures is achieved using γ-cyclodextrin (γ-CD) as a supramolecular connector. The new self-assembled systems, so-called CLUSPOM, are formed from Dawson-type polyoxometalate [PWO] and electron-rich rhenium clusters. It is worth noting that a cluster-based cation [{ReSe}(HO)] on one hand and a cluster-based anion on the other hand [{ReSe}(CN)] can be associated with the anionic POM. In the absence of the supramolecular connector, a "CLUSPOM salt" was obtained from aqueous solution of the cationic cluster and the polyoxometalate. In this solid, the arrangement between the polymetallic building blocks is mainly governed by long-range Coulombic interactions. In the presence of γ-CD, the Dawson anion and the cationic cluster are assembled differently, forming a hierarchical supramolecular solid, K[{ReSe}(HO)]{[PWO]@2γ-CD}·42HO, where the organic macrocycle acts as a ditopic linker between the inorganic building blocks. In such an edifice, the short-range molecular recognition dominates the long-range Coulombic interactions leading to a specific three-dimensional organization. Interestingly, the assembling of anionic POM [PWO] with the anionic rhenium cluster [{ReSe}(CN)] is also achieved with γ-CD despite the repulsive forces between the nanosized anions. The resulting solid, K{[{ReSe}(CN)]@2γ-CD}[PWO]·33HO, is built from 12 inclusion complexes {[{ReSe}(CN)]@2γ-CD} linked by a POM unit interacting with the exterior wall of the organic macrocycle. Multinuclear NMR and small-angle X-ray scattering investigations support supramolecular preorganization in aqueous solution prior to crystallization

Selective conversion of {Mo-132} Keplerate ion into 4-electron reduced crown-capped Keggin derivative Te5Mo15O57 (8-). A key intermediate to single-phase M1 multielement MoVTeO light-alkanes oxidation catalyst

22 Canioni, Romain Marchal-Roch, Catherine Leclerc-Laronze, Nathalie Haouas, Mohamed Taulelle, Francis Marrot, Jerome Paul, Sebastien Lamonier, Carole Paul, Jean-Francois Loridant, Stephane Millet, Jean-Marc M. Cadot, Emmanuel{Mo-132} Keplerate anion reacts with tellurites to give a soluble precursor to produce in hydrothermal conditions single-phase M1 MoVTeO light-alkanes oxidation catalyst. Characterization of this Te-containing intermediate by single-crystal X-ray diffraction, Te-125 NMR, UV-visible and redox titration reveals a molybdotellurite anion as a crown-capped Keggin derivative

Polyoxometalate, Cationic Cluster, and γ-Cyclodextrin: From Primary Interactions to Supramolecular Hybrid Materials

International audienceHerein, we report on a three-component supramolecular hybrid system built from specific recognition processes involving a Dawson-type polyoxometalate (POM), [PWO], a cationic electron-rich cluster [TaBr(HO)], and γ-cyclodextrin (γ-CD). Such materials have been investigated using a bottom-up approach by studying the specific interactions between γ-CD and both types of inorganic units. Their ability to interact has been investigated in the solid state by single-crystal X-ray diffraction (XRD) and in solution using multinuclear NMR methods (including DOSY, EXSY, and COSY), electrospray ionization mass and UV-vis spectroscopies, electrochemistry, and isothermal titration calorimetry experiments. Single-crystal XRD analysis reveals that POM:γ-CD constitutes a highly versatile system which gives aggregates with 1:1, 1:2, and 1:3 stoichiometry. Surprisingly, these arrangements exhibit a common feature wherein the γ-CD moiety interacts with the Dawson-type POMs through its primary face. We present also the first structural model involving an octahedral-type metallic cluster with γ-CD. XRD study reveals that the cationic [TaBr(HO)] ion is closely embedded within two γ-CD units to give a supramolecular ditopic cation, suitable to be used as a linker within extended structure. Solution study demonstrates clearly that pre-associations exist in solution, for which binding constants and thermodynamic parameters have been determined, giving preliminary arguments about the chaotropic nature of the inorganic ions. Finally, both building blocks, i.e., the ditopic supramolecular cation {[TaBr(HO)]@2CD} and the Dawson-type anion, react together to give a three-component, well-ordered hybrid material derived either as a supramolecular hydrogel or single crystals. The solid-state structure shows an unprecedented helicoidal tubular chain resulting from the periodic alternation of POM and supramolecular cation, featuring short hydrogen-bonding contacts between the electron-poor POM and electron-rich cluster. The 1D tubular ionic polymer observed in the single crystals should make it possible to understand the long-range ordering observed within the hydrogel hybrid material. The supramolecular chemical complementarities between the γ-CD-based ditopic cation and POM open a wide scope for the design of hybrid materials that accumulate synergistic functionalities

"Bottom-Up" Meets "Top-Down" Assembly in Nanoscale Polyoxometalate Clusters: Self-Assembly of [P4W52O178](24-) and Disassembly to [P3W39O134](19-)

The pH-controlled assembly/disassembly of a nanoscale {P4W52O178}(24-) cluster at pH 2 to a {P4W44O152}(20-) cluster at pH 3 -5 via a {P3W39O134)(19-) cluster species at pH 2-3 to finally give {P2W19O69(OH2)}(14-) at pH 6 is reported. This process can be traced in the solid state crystallographically and in solution using dynamic light scattering studies

Self-assembly of a nanosized, saddle-shaped, solution-stable polyoxometalate anion built from pentagonal building blocks: [H34W119Se8Fe2O420](54-)

Precise control of the "one-pot" reaction conditions is employed for the assembly of a nanosized 2.8 nm cluster, [H34W119Se8Fe2O420](54-) (1a), which is templated using eight selenite units and two iron(III) centers. Not only is this cluster characterized structurally using X-ray crystallography, it is the largest polyoxotungstate to be observed intact in solution using ESI-MS, with a molecular mass of ca. 30 000 Da

183W INADEQUATE 2D NMR Spectroscopy of Hetero Arsenato–Phosphato–Tungstate PV/AsV Substitution in Dawson-Type α-[AsxP2–xW18O62]6– (x = 0–2) and α-[H4AsyP1–yW18O62]7– (y = 0, 1)

International audienceThe Dawson-type arsenato-phosphato-tungstate alpha-[AsPW18O62](6-) has been prepared and unambiguously identified for the first time. A comparative study. including the four other already known compounds, the symmetric alpha-[X2W18O62](6-) and unsymmetric alpha-[H4XW18O62](7-) for X = P-V, As-V, has been performed by spectroscopic W-183 and P-31 NMR. 2-D W-183 INADEQUATE experiments were systematically employed to unequivocally verify structures, assign all resonances, and determine precisely (2)J(W-O-W) scalar couplings. The effects of P/As substitutions, generating unsymmetric structures, on the NMR observables delta(W-183), delta(P-31), (2)J(W-O-W), and (2)J(W-O-P) are discussed in relation to their bond length and bond angle alteration. General trends with respect to NMR parameter variations have been found when filling central cavities with P or As atoms, with less pronounced effects for As than for P. In addition, NMR characterization of three other isomers, i.e., beta-[X2W18O62](6-) and [As2W18O62](6-), were also provided for comparison. The present NMR results could serve as representative reference data for understanding the relationship between structure and NMR observables in polyoxotungstates