Single polyoxometalate-based nanoclusters characterized by infrared absorption nanospectroscopy.

Bottom-up engineering is a very attractive field. However, the periodic organization of molecules on a solid substrate is challenging, particularly in the selection of the appropriate characterization technique which is suitable for both large area and accurate analysis at the nanoscale. Here, this study demonstrates the unambiguous identification of complex molecular layers by infrared absorption microscopy at the nanometric scale.

Halide-free CO cycloaddition onto styrene oxide catalysed by first row transition-metal derivatives of polyoxotungstates.

Quaternary ammonium salts of metal derivatives of polyoxometalates [XWOM(HO)] (X = P, Si; M = Cr, Mn, Co, Ni, Zn) were successfully tested instead of quaternary ammonium halides as catalysts in the cycloaddition of CO to styrene oxide. Remarkably, they gave very satisfactory yields of styrene carbonate at moderate temperature (80 °C).

Ready-to-be-addressed oxo-clusters: individualized, periodically organized and separated from the substrate.

Clusters and oxo-clusters are drawing attention for their amazing physical properties, especially at the scale of the single molecule. However, chemical methods to organize them individually on a surface are still lacking. In this study we show that it is possible to periodically organize individual polyoxometalates thanks to their ordering by a new supramolecular assembly.

Experimental observation of the role of countercations in modulating the electrical conductance of Preyssler-type polyoxometalate nanodevices.

Polyoxometalates are nanoscale molecular oxides with promising properties that are currently explored for molecule-based memory devices. In this work, we synthesize a series of Preyssler polyoxometalates (POMs), [Na⊂PWO], stabilized with four different counterions, H, K, NH, and tetrabutylammonium (TBA). We study the electron transport properties at the nanoscale (conductive atomic force microscopy, C-AFM) of molecular junctions formed by self-assembled monolayers (SAMs) of POMs electrostatically deposited on the ultraflat gold surface prefunctionalized with a positively charged SAM of amine-terminated alkylthiol chains.

Multi-Electron Visible Light Photoaccumulation on a Dipyridylamine Copper(II)-Polyoxometalate Conjugate Applied to Photocatalytic Generation of CF Radicals.

This article describes the synthesis and characterization of an organic-inorganic hybrid polyoxometalate functionalized by a short link with a tripodal N-based ligand and its copper complex. Upon visible light irradiation, the latter is able to store up to three reducing equivalents. The locus of the reduction is discussed based on physicochemical measurements and DFT calculations.

Correction: Redox-controlled conductance of polyoxometalate molecular junctions.

Correction for 'Redox-controlled conductance of polyoxometalate molecular junctions' by Cécile Huez , , 2022, , 13790-13800, https://doi.org/10.1039/D2NR03457C.

Redox-controlled conductance of polyoxometalate molecular junctions.

We demonstrate the reversible photoreduction of molecular junctions of a phosphomolybdate [PMoO] monolayer self-assembled on flat gold electrodes, connected by the tip of a conductive atomic force microscope. The conductance of the one electron reduced [PMoO] molecular junction is increased by ∼10, and this open-shell state is stable in the junction in air at room temperature. The analysis of a large current-voltage dataset by unsupervised machine learning and clustering algorithms reveals that the electron transport in the pristine phosphomolybdate junctions leads to symmetric current-voltage curves, controlled by the lowest unoccupied molecular orbital (LUMO) at 0.

Lennard-Jones interaction parameters of Mo and W in He and N from collision cross-sections of Lindqvist and Keggin polyoxometalate anions.

Drift tube ion mobility spectrometry (DTIMS) coupled with mass spectrometry was used to determine the collision cross-sections (CCS) of polyoxometalate anions in helium and nitrogen. As the geometry of the ion, more than its mass, determines the collision cross-section with a given drift gas molecule, we found that both Lindqvist ions MoO and WO had a CCS value of 103 ± 2 Å, and both Keggin ions PMoO and PWO had a CCS value of 170 ± 2 Å. Similarly, ion mobility experiments in N led to CCS values of 223 ± 2 Å and 339 ± 4 Å for Lindqvist and Keggin anions, respectively.

When Identification of the Reduction Sites in Mixed Molybdenum/Tungsten Keggin-Type Polyoxometalate Hybrids Turns Out Tricky.

The mixed molybdenum/tungsten Keggin-type polyoxometalate (POM) hybrid (TBA)[PWMoO{Sn(CHI)}] (TBA = -butylammonium) has been prepared by the reaction between [α-PWMoO] and [ClSn(CHI)] in dried acetonitrile, in the presence of tetra--butylammonium bromide. A further coupling reaction affords the ferrocenyl derivative (TBA)[PWMoO{Sn(CH)C≡C(CH)Fc}]. The POM hybrids have been thoroughly characterized by NMR and IR spectroscopies.

Exploring the self-assembly of dumbbell-shaped polyoxometalate hybrids, from molecular building units to nanostructured soft materials.

The formation of hierarchical nanostructures using preformed dumbbell-like species made of covalent organic-inorganic polyoxometalate (POM)-based hybrids is herein described. In this system, the presence of charged subunits (POM, metal linkers, and counter ions) in the complex molecular architecture can drive their aggregation, which results from a competition between the solvation energy of the discrete species and intermolecular electrostatic interactions. We show that the nature of the POM and the charge of the metal linker are key parameters for the hierarchical nanoorganization.

Photoactive Organic/Inorganic Hybrid Materials with Nanosegregated Donor-Acceptor Arrays.

The synthesis of the first mesogenic donor-acceptor polyoxometalate (POM)-based hybrid is herein described. The structural and electronic properties of the hybrid compound were evaluated through combination of small- and wide-angle X-ray scattering, optical microscopy, electrochemistry and photoluminescence. In the solid state, the compound behaves as a birefringent solid, displaying a lamellar organization in which double-layers of POMs and bis(thiophene)thienothiophene organic donors alternate regularly.

Tuning Photoinduced Electron Transfer in POM-Bodipy Hybrids by Controlling the Environment: Experiment and Theory.

The optical and electrochemical properties of a series of polyoxometalate (POM) oxoclusters decorated with two bodipy (boron-dipyrromethene) light-harvesting units were examined. Evaluated here in this polyanionic donor-acceptor system is the effect of the solvent and associated counterions on the intramolecular photoinduced electron transfer. The results show that both solvents and counterions have a major impact upon the energy of the charge-transfer state by modifying the solvation shell around the POMs.

Covalent Grafting of Polyoxometalate Hybrids onto Flat Silicon/Silicon Oxide: Insights from POMs Layers on Oxides.

Immobilization of polyoxometalates (POMs) onto oxides is relevant to many applications in the fields of catalysis, energy conversion/storage, or molecular electronics. Optimization and understanding the molecule/oxide interface is crucial to rationally improve the performance of the final molecular materials. We herein describe the synthesis and covalent grafting of POM hybrids with remote carboxylic acid functions onto flat Si/SiO substrates.

Hierarchical Self-Assembly of Polyoxometalate-Based Organo Palladium(II) Metallomacrocycles via Electrostatic Interactions.

The design and synthesis of a supramolecular square composed of polyoxometalate-based hybrid donors and ethylenediamine palladium(II) nodes are reported. The structure of the metallomacrocycle scaffold was inferred by diffusion NMR, small-angle X-ray scattering (SAXS), and molecular modeling. The metallomacrocycle scaffold that contains negatively and positively charged subunits can further self-assemble owing to a competition between the solvation energy of the discrete species and intermolecular electrostatic interactions.

Protective Effect of Polyoxometalates in {Mo}/Maghemite Binary Superlattices Under Annealing.

The binary assembly DDA-{Mo}/OA-γ-FeO (DDA = didodecyldimethylammonium, {Mo} = [MoO(CHCOO)(HO)], OA = oleic acid) constitutes one of the two examples in the literature of binary superlattices made of a mixing of nanocrystals and oxo-clusters. In a precedent work, we reported in details the preparation of such magnetic binary systems and studied the effect of the nature of the polyoxometalates (POMs) on the magnetic properties. In the present paper, we study the stability of this model binary assembly under heating at various temperatures.

Modeling the Oxygen Vacancy at a Molecular Vanadium(III) Silica-Supported Catalyst.

Here we report on the use of a silanol-decorated polyoxotungstate, [SbWO( BuSiOH)] (1), as a molecular support to describe the coordination of a vanadium atom at a single-site on silica surfaces. By reacting [V(Mes)·thf] (Mes = 2,4,6-trimethylphenyl) with 1 in tetrahydrofuran, the vanadium(III) derivative [SbWO( BuSiO)V(thf)] (2) was obtained. Compound 2 displays the paramagnetic behavior expected for a d-V high spin complex (SQUID measurements) with a triplet electronic ground state (ca.

Molecular signature of polyoxometalates in electron transport of silicon-based molecular junctions.

Polyoxometalates (POMs) are unconventional electro-active molecules with a great potential for applications in molecular memories, providing efficient processing steps onto electrodes are available. The synthesis of the organic-inorganic polyoxometalate hybrids [PM11O39{Sn(C6H4)C[triple bond, length as m-dash]C(C6H4)N2}]3- (M = Mo, W) endowed with a remote diazonium function is reported together with their covalent immobilization onto hydrogenated n-Si(100) substrates. Electron transport measurements through the resulting densely-packed monolayers contacted with a mercury drop as a top electrode confirms their homogeneity.

Control of the hierarchical self-assembly of polyoxometalate-based metallomacrocycles by redox trigger and solvent composition.

Discrete metallomacrocycles are attractive scaffolds for the formation of complex supramolecular architectures with emergent properties. We herein describe the formation of hierarchical nanostructures using preformed metallomacrocycles by coordination-driven self-assembly of a covalent organic-inorganic polyoxometalate (POM)-based hybrid. In this system, we take advantage of the presence of charged subunits (POM, metal linker, and counterions) within the metallomacrocycles, which drive their aggregation through intermolecular electrostatic interactions.

Rapid photoinduced charge injection into covalent polyoxometalate-bodipy conjugates.

Controlled design of photoactive hybrids would provide highly active materials for solar energy conversion and photo(electro) catalysis. We describe the kinetics of photoinduced electron transfer in a series of photoactive hybrids based on Keggin-type polyoxometalates (POMs) covalently grafted to bodipy photosensitizers. We show how the electronic properties and corresponding dynamics of these hybrids can be readily tuned by varying the POM metal ion, the anchoring functionalization and the spacer length.

A calibration framework for the determination of accurate collision cross sections of polyanions using polyoxometalate standards.

Rationale: Polyoxometalates (POMs) are remarkable oxo-clusters forming compact highly charged anions. We measured their collision cross sections (CCS) in N with drift tube ion mobility spectrometry (DTIMS). These values were then used to calibrate a traveling wave ion mobility spectrometry (TWIMS) device and the accuracy of the calibration was tested.

Self-assembly study of nanometric spheres from polyoxometalate-phenylalanine hybrids, an experimental and theoretical approach.

Herein, we report on the study of supramolecular assemblies based on polyoxometalates (POMs) upon their modification with amino acids. Two POM-amino acid hybrids were synthesized by coupling a functionalized Keggin type polyoxoanion [PW11O39{Sn(C6H4)C[triple bond, length as m-dash]C(C6H4)COOH}]4- with carboxyl-protected (methyl-ester) phenylalanine or diphenylalanine peptides. Surprisingly, all compounds, including the initial POM, formed supramolecular nanospheres in different solvent mixtures, which were examined by scanning electron microscopy (SEM).

Polyoxometalates in the Hofmeister series.

We propose a simple experimental procedure based on the cloud point measurement of a non-ionic surfactant as a tool for (i) estimating the super-chaotropic behaviour of polyoxometalates (POMs) and for (ii) establishing a classification of POMs according to their affinity towards polar surfaces.

Heteropolytungstate-decorated core-shell magnetic nanoparticles: A covalent strategy for polyoxometalate-based hybrid nanomaterials.

Amino-functionalized core-shell magnetic nanoparticles have been covalently grafted with Polyoxometalates (POMs). These multifunctional nanocomposites have been obtained through the coupling of heteropolytungstate-based hybrids bearing carboxylic acid functions with aminopropyl functions that decorate the core-shell nanoparticles. The physical properties of the resulting materials have been studied by a large set of techniques.