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This paper deals with the electrochemical properties of three iso-structural compounds of general formula [SiW$_{10}$ O$_{36}$(M$_{2}$O$_{2}$E$_{2}$)]$^{6-}$ (M $=$ Mo or W; E $=$ S or O). A first part is focused on their electrochemical behaviors in aqueous medium. A second part concerns the electrocatalytic properties of these compounds in aqueous medium and the preparation of modified glassy carbon electrodes through a layer-by-layer methodology. This method allowed preparing a multilayer system, which was applied to the electroanalysis of iodate anions in aqueous medium with a limit detection of $6.2~\mu \mbox {M}$.

Supramolecular polymers built from stimuli‐responsive host‐guest interactions represent an attractive way of tailoring smart materials. Herein, we exploit the chaotropic effect of polyoxometalates and related host‐guest properties to design unconventional polymer systems with reversible redox and thermo‐responsive sol‐gel transition. These supramolecular networks result from the association of cyclodextrin‐based oligomers and Keggin‐type POMs acting as electro‐active crosslinking agents. The structure and the dynamics of such self‐assembly systems have been investigated using a multiscale approach involving MALDI‐TOF, viscosity measurements, cyclic voltammetry, 1H‐NMR (1D and DOSY), and Small‐Angle X‐ray Scattering. Our results reveal that the chaotropic effect corresponds to a powerful and efficient force that can be used to induce responsiveness in hybrid supramolecular oligomeric systems. [ABSTRACT FROM AUTHOR]

Super‐reduction of polyoxometalates (POMs) in solution is of fundamental interest for designing innovative energy storage systems. In this article, we show that the "Dawson‐like" POM can undergo a disproportionation process during its massive electron uptake, leading to species containing three metal‐metal bonds as evidenced by X‐ray diffraction, multi‐nuclear magnetic resonance spectroscopy (1H and 183W NMR), extended X‐ray absorption fine structure (EXAFS), UV/Vis, and voltammetry techniques. This result indicates that electron storing within metal‐metal bonds is not a unique property of Keggin‐type POM as postulated since the 70s. Besides, we demonstrate that the presence of an electron‐rich triad in the "Dawson‐like" POM allows its post‐functionalization with additional tungstate ions, generating a chiral molecule that is also the largest WIV‐containing POMs known to date. [ABSTRACT FROM AUTHOR]

Natural cyclodextrin (CD) macrocycles are known to form diverse inclusion complexes with a wide variety of organic molecules, but recent work has revealed that inorganic clusters also form multicomponent supramolecular complexes and edifices. Such molecular assemblies exhibit a high degree of organization in solution governed by various chemical processes including molecular recognition, host-guest attraction, hydrophobic repulsion, or chaotropic effect. Nuclear magnetic resonance (NMR) spectroscopy is one of the most efficient and practical analytical techniques to characterize the nature, the strength and the mechanism of these interactions in solution. This review provides a brief overview on recent examples of the contribution of NMR to the characterization of hybrid systems in solution based on CD with polynuclear clusters, including polyoxometalates (POMs), metallic clusters and hydroborate clusters. The focus will be first on using ¹H (and 13C) NMR of the host, i.e., CD, to identify the nature of the interactions and measure their strength. Then, 2D NMR methods will be illustrated by DOSY as a means of highlighting the clustering phenomena, and by NOESY/ROESY to evidence the spatial proximity and contact within the supramolecular assemblies. Finally, other NMR nuclei will be selected to probe the inorganic part as a guest molecule. Attention will be paid to classical host-guest complexes Cluster@CD, but also to hierarchical multi-scale, multi-component assemblies such as Cluster@CD@Cluster. [ABSTRACT FROM AUTHOR]

Evidence for photoinduced intermolecular electron transfer from the excited state of the [Mo6I8Cl6]2− electron-rich cluster to polyoxometalates (POMs) is reported. We demonstrate that the global charge density of POMs affects the efficiency of electron transfer. This work paves the way for the rational design of photocatalytic systems using cluster-based complexes as robust noble-metal-free photosensitizers. [ABSTRACT FROM AUTHOR]

Host–guest assemblies open up opportunities for developing novel functional CLUSPOM multicomponent systems based on transition metal clusters (CLUS), polyoxometalates (POMs) and macrocyclic organic ligands. In water–ethanol solution γ-cyclodextrin (γ-CD) interacts with halide metal clusters [M6Cl14]2– (M = Mo, W) to form sandwich-type structures. The supramolecular association between the clusters and CDs, however, remains weak in solution, and the interactions are not strong enough to prevent the hydrolysis of the inorganic guest. Although analysis of the resulting crystal structures reveals inclusion complexation, 1H NMR experiments in solution show no specific affinity between the two components. The luminescent properties of the host–guest compounds in comparison with the initial cluster complexes are also studied to evaluate the influence of CD. [ABSTRACT FROM AUTHOR]

Noncovalent ionic interactions between nanosized Keplerate-type capsules {Mo132} and tetra-cationic porphyrins have been investigated in aqueous solution using small-angle X-ray scattering, 1H NMR and photophysical methods. These complementary multiscale methods reveal the formation of large hybrid oligomers built from a short-range organization in which the cationic porphyrin is glued onto the large POM surface. The local structuring appears to be strongly dependent on the dye : {Mo132} ratio changing the morphology of the oligomers from linear to dense aggregates. [ABSTRACT FROM AUTHOR]

Herein we report the synthesis of a new class of compounds associating Keggin and Dawson-type Polyoxometalates (POMs) with a derivative of the anionic decahydro-closo-decaborate cluster [B10H10]2− through aminopropylsilyl ligand (APTES) acting as both a linker and a spacer between the two negatively charged species. Three new adducts were isolated and fully characterized by various NMR techniques and MALDI-TOF mass spectrometry, notably revealing the isolation of an unprecedented monofunctionalized SiW10 derivative stabilized through intramolecular H-H dihydrogen contacts. DFT as well as electrochemical studies allowed studying the electronic effect of grafting the decaborate cluster on the POM moiety and its consequences on the hydrogen evolution reaction (HER) properties. [ABSTRACT FROM AUTHOR]

Polyphosphate ions are found to react easily with cyclic oxothiomolybdic backbone, allowing the formation of encapsulated substrates. Their molecular composition, formed in the solid phase, explains the versatility and abilities of these compounds.

The pure gamma isomer of the Keggin ion is crystallized as a tetrabutylammonium salt in a mixed H2O/CH(sub 3)CN solvent and is fully structurally characterized by single-crystal X-ray diffraction. The electronic behavior of the 2-electron-reduced oxo and oxothio derivatives are discussed and are related to the nature of the ligand E (O or S) and the metal (W or Mo).

A synthesis of five reduced polyoxomolybdate anions is presented. The use of IR spectroscopy, hydrothermal reactions and redox titrations is described.

Polyoxothiometalate ions (ThioPOM) are active hydrogen‐evolution reaction (HER) catalysts based on modular assembly built from electrophilic clusters {MoSx} and vacant polyoxotungstates. Herein, the dumbbell‐like anion [{(PW11O39)Mo3S4(H2O)3(OH)}2]8− exhibits very high light‐driven HER activity, while the active cores {Mo3S4} do not contain any exposed disulfido ligands, which were suspected to be the origin of the HER activity. Moreover, in the catalyst architecture, the two central {Mo3S4} cores are sandwiched by two {PW11O39}7− subunits that act as oxidant‐resistant protecting groups and behave as electron‐collecting units. A detailed photophysical study was carried out confirming the reductive quenching mechanism of the photosensitizer [Ir(ppy)2(dtbbpy)]+ by the sacrificial donor triethanolamine (TEOA) and highlighting the very high rate constant of the electron transfer from the reduced photosensitizer to the ThioPOM catalyst. Such results provide new insights into the field of molecular catalytic systems able to promote high HER activity. [ABSTRACT FROM AUTHOR]

The redox parameters of the Keggin anions alpha-(SiMo3-xVxW9O40)(4+x)- and alpha-(PMo3-xVxW9O40)(3+x)-, with X = 1, 2, or 3, are presented. The one-electron-reduced species were prepared by electrolysis and characterized by ESR spectroscopy both in solution and solid state. The results showed that the ESO spectra of the V4+ ion is dependent on the surrounding atoms, Mo(V)I, W(VI) and V(V). The electron hopping and delocalization characteristics of di and trivanadium compounds were also determined.

Host‐guest complexes between native cyclodextrins (α‐, β‐ and γ‐CD) and hybrid Lindqvist‐type polyoxovanadates (POVs) [V6O13((OCH2)3C−R)2]2– with R = CH2CH3, NO2, CH2OH and NH(BOC) (BOC = N‐tert‐butoxycarbonyl) were studied in aqueous solution. Six crystal structures determined by single‐crystal X‐ray diffraction analysis revealed the nature of the functional R group strongly influences the host–guest conformation and also the crystal packing. In all systems isolated in the solid‐state, the organic groups R are embedded within the cyclodextrin cavities, involving only a few weak supramolecular contacts. The interaction between hybrid POVs and the macrocyclic organic hosts have been deeply studied in solution using ITC, cyclic voltammetry and NMR methods (1D 1H NMR, and 2D DOSY, and ROESY). This set of complementary techniques provides clear insights about the strength of interactions and the binding host‐guest modes occurring in aqueous solution, highlighting a dramatic influence of the functional group R on the supramolecular properties of the hexavanadate polyoxoanions (association constant K1:1 vary from 0 to 2 000 M−1) while isolated functional organic groups exhibit only very weak intrinsic affinity with CDs. Electrochemical and calorimetric investigations suggest that the driving force of the host‐guest association involving larger CDs (β‐ and γ‐CD) is mainly related to the chaotropic effect. In contrast, the hydrophobic effect supported by weak attractive forces appears as the main contributor for the formation of α‐CD‐containing host‐guest complexes. In any cases, the origin of driving forces is clearly related to the ability of the macrocyclic host to desolvate the exposed moieties of the hybrid POVs. [ABSTRACT FROM AUTHOR]

Alpha-(SiMo2W10O40)4-, alpha-(SiMo3W9O40)4- and alpha-(SiMo2VW9O40)5- were yielded from the anion alpha-(SiW9O34)10- by a synthetic route through the monovacant anion alpha-(SiMo2W9O39)8-. The NMR study of the Keggin heteropolytungstates showed homonuclear 2J(sub W-O-W) coupling constants in the range 21-22 Hz for corner coupling and 5-7 Hz for edge coupling. The compounds with metallic vacancies revealed a wider distribution of coupling constant values.

Herein, we show how the chaotropic effect arising from reduced molybdate ions in acidified aqueous solution is able to amplify drastically weak supramolecular interactions. Time‐resolved Small Angle X‐ray Scattering (SAXS) analysis suggests that molybdenum‐blue oligomeric species form huge aggregates in the presence of γ‐cyclodextrin (γ‐CD) which results in the fast formation of nanoscopic {Mo154}‐based host‐guest species, while X‐ray diffraction analysis reveals that the ending‐point of the scenario results in an unprecedented three‐component well‐ordered core–shell‐like motif. A similar arrangement was found by using preformed hexarhenium chalcogenide‐type cluster [Re6Te8(CN)6]4− as exogenous guest. This seminal work brings better understanding of the self‐assembly processes in general and gives new opportunities for practical applications in the design of complex multicomponent materials via the simplicity of the non‐covalent chemistry. [ABSTRACT FROM AUTHOR]

We report on the synthesis, structure, and physicochemical characterization of the first three examples of neutral palladium‐oxo clusters (POCs). The 16‐palladium(II)‐oxo cluster [Pd16O24(OH)8((CH3)2As)8] (Pd16) comprises a cyclic palladium‐oxo unit capped by eight dimethylarsinate groups. The chloro‐derivative [Pd16Na2O26(OH)3 Cl3 ((CH3)2 As)8] (Pd16Cl) was also prepared, which forms a highly stable 3D supramolecular lattice via strong intermolecular interactions. The 24‐palladium(II)‐oxo cluster [Pd24O44(OH)8((CH3)2As)16] (Pd24) can be considered as a bicapped derivative of Pd16 with a tetra‐palladium‐oxo unit grafted on either side. The three compounds were fully characterized 1) in the solid state by single‐crystal and powder XRD, IR, TGA, and solid‐state 1H and 13C NMR spectroscopy, 2) in solution by 1H, 13C NMR and 1H DOSY spectroscopic methods, and 3) in the gas phase by electrospray ionization mass spectrometry (ESI‐MS). [ABSTRACT FROM AUTHOR]

We report on the synthesis, structure, and physicochemical characterization of the first three examples of neutral palladium‐oxo clusters (POCs). The 16‐palladium(II)‐oxo cluster [Pd16O24(OH)8((CH3)2As)8] (Pd16) comprises a cyclic palladium‐oxo unit capped by eight dimethylarsinate groups. The chloro‐derivative [Pd16Na2O26(OH)3 Cl3 ((CH3)2 As)8] (Pd16Cl) was also prepared, which forms a highly stable 3D supramolecular lattice via strong intermolecular interactions. The 24‐palladium(II)‐oxo cluster [Pd24O44(OH)8((CH3)2As)16] (Pd24) can be considered as a bicapped derivative of Pd16 with a tetra‐palladium‐oxo unit grafted on either side. The three compounds were fully characterized 1) in the solid state by single‐crystal and powder XRD, IR, TGA, and solid‐state 1H and 13C NMR spectroscopy, 2) in solution by 1H, 13C NMR and 1H DOSY spectroscopic methods, and 3) in the gas phase by electrospray ionization mass spectrometry (ESI‐MS). [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis of N-tert-butoxycarbonyl (BOC) protected [V6O13{(OCH2)3C–NH2}2]2− built from the Lindqvist-type hexavanadate. The reaction of di-tert-butyl dicarbonate (BOC2O) with tris(hydroxymethyl)aminomethane (Tris) led to the organic derivative [(OCH2)3C–NH(BOC)] that reacts with the decavanadate in dimethylacetamide (DMA) to form the [V6O13{(OCH2)3 C–NH(BOC)}2]2− anion. The tetrabutylammonium (TBA+) salt of this hybrid polyoxovanadate, TBA2[V6O13{(OCH2)3C–NH(BOC)}2]· 2DMA, has been characterized in the solid-state by single-crystal X-ray diffraction and infrared spectroscopy, and in solution by multinuclear (1H, 13C, 15N and 51V) and DOSY NMR, and UV–visible spectroscopy. [ABSTRACT FROM AUTHOR]

Specific molecular recognition of γ‐cyclodextrin (γ‐CD) by the cationic hexanuclear niobium [Nb6Cl12(H2O)6]2+ cluster complex in aqueous solutions results in a 1:1 supramolecular assembly {[Nb6Cl12(H2O)6]@γ‐CD}2+. NMR spectroscopy, isothermal titration calorimetry (ITC), and ESI‐MS were used to study the interaction between the inorganic cluster and the organic macrocycle. Such molecular association affects the biological activity of [Nb6Cl12(H2O)6]2+, decreasing its cytotoxicity despite enhanced cellular uptake. The 1:1 stoichiometry is maintained in solution over a large window of the reagents' ratio, but crystallization by slow evaporation produces a 1:2 host–guest complex [Nb6Cl12(H2O)6@(γ‐CD)2]Cl2⋅20 H2O featuring the cluster encapsulated between two molecules of γ‐CD. The 1:2 complex was characterized by XRD, elemental analysis, IR spectroscopy, and thermogravimetric analysis (TGA). Quantum chemical calculations were performed to model host–guest interaction. [ABSTRACT FROM AUTHOR]