Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 66
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Inorg Chem ; 2020 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-31977199

RESUMO

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. When the dissociating character of the solvent was lowered or when in the presence of a protic solvent, different types of multiscale organizations (vesicles and pseudo-1D structures) were selectively formed and were characterized by SAXS and transmission electron microscopy.

2.
J Am Chem Soc ; 140(44): 14903-14914, 2018 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-30362733

RESUMO

Here we report on the use of a silanol-decorated polyoxotungstate, [SbW9O33( tBuSiOH)3]3- (1), as a molecular support to describe the coordination of a vanadium atom at a single-site on silica surfaces. By reacting [V(Mes)3·thf] (Mes = 2,4,6-trimethylphenyl) with 1 in tetrahydrofuran, the vanadium(III) derivative [SbW9O33( tBuSiO)3V(thf)]3- (2) was obtained. Compound 2 displays the paramagnetic behavior expected for a d2-VIII high spin complex (SQUID measurements) with a triplet electronic ground state (ca. 30 kcal·mol-1 more stable than the singlet, from DFT calculations). Compound 2 proves to be a reliable model for reduced isolated-vanadium atom dispersed on silica surfaces [(≡Si-O)3VIII(OH2)], an intermediate that is often proposed in a Mars-van Krevelen type mechanism for partial oxidation of light alcohols. Oxidation of 2 under air produced the oxo-derivative [SbW9O33( tBuSiO)3VO]3- (3). In compound 2, the d2-electrons are localized in degenerated d(V) orbitals, whereas in the electronically analogous bireduced-[SbW9O33( tBuSiO)3VO]5-, 3·(2e), one electron is localized on d(V) orbital and the second one is delocalized on the polyoxotungstic framework, leading to a unique case of a bireduced heteropolyanion derivative with completely decoupled d1-V(IV) and d1-W(V). Our body of experimental results (EPR, magnetic measurements, spectroelectrochemical studies, Raman spectroscopy) and theoretical studies highlights (i) the role of the apical ligand coordination, i.e., thf (σ-donor) vs oxo (π-donor), in destabilizing or stabilizing the d(V) orbitals relative to the d(W) orbitals, and (ii) a geometrical distortion of the O3VO entity that causes a splitting of the degenerated orbitals and the stabilization of one d(V) orbital in the bireduced compound 3·(2e).

3.
Nanoscale ; 10(36): 17156-17165, 2018 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-30187072

RESUMO

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. Adjustment of the current-voltage curves with the Simmon's equation gives a mean tunnel energy barrier ΦPOM of 1.8 eV and 1.6 eV, for the Silicon-Molecules-Metal (SMM) junctions based on the polyoxotungstates (M = W) and polyoxomolybdates (M = Mo), respectively. This follows the trend observed in the electrochemical properties of POMs in solution, the polyoxomolybdates being easier to reduce than the polyoxotungstates, in agreement with lowest unoccupied molecular orbitals (LUMOs) of lower energy. The molecular signature of the POMs is thus clearly identifiable in the solid-state electrical properties and the unmatched diversity of POM molecular and electronic structures should offer a great modularity.

4.
Proc Natl Acad Sci U S A ; 115(36): 8895-8900, 2018 09 04.
Artigo em Inglês | MEDLINE | ID: mdl-30131428

RESUMO

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. We show that the solvent composition and the charge of the metal linker are key parameters that steer the supramolecular organization. Different types of hierarchical self-assemblies, zero-dimensional (0D) dense nanoparticles, and 1D worm-like nanoobjects, can be selectively formed owing to different aggregation modes of the metallomacrocycles. Finally, we report that the worm-like structures drastically enhance the solubility in water of a pyrene derivative and can act as molecular carriers.

5.
Chem Sci ; 9(25): 5578-5584, 2018 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-30061989

RESUMO

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. Ultrafast visible and IR transient absorption spectroscopy, supported by spectroelectrochemical measurements, reveals that photoinduced electron transfer from the bodipy chromophore to the organosilyl POM derivative occurs as rapidly as τ = 54 ps to generate a long-lived (τ = 4.8 ns) charge-separated (CS) state, making this system appropriate for applications in photoelectrochemical devices.

6.
Rapid Commun Mass Spectrom ; 32(19): 1703-1710, 2018 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-29989245

RESUMO

RATIONALE: Polyoxometalates (POMs) are remarkable oxo-clusters forming compact highly charged anions. We measured their collision cross sections (CCS) in N2 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. METHODS: Six POM standards were analyzed by DTIM-MS (Tofwerk, Thun, Switzerland) at different voltages to determine absolute DT CCS (N2 ) values. Five POM compounds (Lindqvist TBA2 Mo6 O19; decatungstate TBA4 W10 O32; Keggin TBA3 PMo12 O40 ; TBA3 PW12 O40 and Dawson TBA6 P2 W18 O62 ) were used for the calibration of the TWIM-MS instrument (Synapt G2 HDMS, Waters, Manchester, UK) and a sixth Dawson POM, TBA9 P2 Nb3 W15 O62 , was used to compare the accuracy of the calibrations with POM or with polyalanine and dextran reference ions. RESULTS: We determined 45 DT CCS (N2 ) values at 30°C or 60°C. Fourteen DT CCS (N2 ) values at 30°C were used to perform calibration of the TWIMS instrument. Better correlations were observed than when DT CCS values in helium from the literature were used. The accuracy tests on six ions of Dawson POM TBA9 P2 Nb3 W15 O62 led to relative errors below 3.1% while relative errors of 3.6% to 10.1% were observed when calibration was performed with polyalanine and dextran reference ions. CONCLUSIONS: Our novel calibration strategy for determination of CCS values of multiply negatively charged ions on TWIM-MS devices based on DT CCS (N2 ) of standard POM structures covered a wider range of CCS and improved the accuracy to 2.1% relative error on average compared with 6.9% using polyalanine and dextran calibration.

7.
Dalton Trans ; 47(18): 6304-6313, 2018 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-29658016

RESUMO

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). Molecular dynamics (MD) simulations for the POM-amino acid species revealed that the hydrophobic forces are mainly responsible for the initial aggregation into incipient micelle type structures, in which the organic arms are buried inside the aggregate while POM polar heads are more exposed to the solvent with tetrabutyl-ammonium counter cations acting as linkers.


Assuntos
Compostos Organometálicos/síntese química , Fenilalanina/química , Teoria Quântica , Compostos de Tungstênio/química , Microscopia Eletrônica de Varredura , Simulação de Dinâmica Molecular , Estrutura Molecular , Compostos Organometálicos/química , Tamanho da Partícula , Propriedades de Superfície
8.
Chem Commun (Camb) ; 54(15): 1833-1836, 2018 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-29308490

RESUMO

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.

9.
J Colloid Interface Sci ; 514: 49-58, 2018 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-29241078

RESUMO

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. The very good nanostructuration of the POMs at the surface of the obtained nanoparticles have thus been directly observed by high-resolution transmission electronic microscopy (HR-TEM). Furthermore, the hyperthermia properties of these nanocomposites have been also considered as a function of the size of the magnetic core. Finally, the stability of these suspensions in organic media makes them particularly interesting in the frame of their processing or their potential use as nanocatalysts.

10.
Inorg Chem ; 56(14): 8490-8496, 2017 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-28682066

RESUMO

The metal-driven self-assembly of a Keggin-based hybrid bearing two remote pyridine units was investigated. The resulting supramolecular species were identified by combination of 2D diffusion NMR spectroscopy (DOSY) and electrospray ionization mass spectrometry (ESI-MS) as a mixture of molecular triangles and squares. This behavior is different from that of the structural analogue Dawson-based hybrid displaying a higher charge, which only led to the formation of molecular triangles. This study highlights the decisive effect of the charge of the POMs in their self-assembly processes that disfavors the formation of large assemblies. An isothermal titration calorimetry (ITC) experiment confirmed the stronger binding in the case of the Keggin hybrids. A correlation between the diffusion coefficient D and the molecular mass M of the POM-based building block and its coordination oligomers was also observed. We show that the diffusion coefficient of these compounds is mainly determined by their occupied volume rather than by their shape.

11.
Angew Chem Int Ed Engl ; 56(17): 4872-4876, 2017 04 18.
Artigo em Inglês | MEDLINE | ID: mdl-28338296

RESUMO

The photophysical properties of a Keggin-type polyoxometalate (POM) covalently bounded to a benzospiropyran (BSPR) unit have been investigated. These studies reveal that both closed and open forms are emissive with distinct spectral features (λem (closed form)=530 nm, λem (open form)=670 nm) and that the fluorescence of the BSPR unit of the hybrid is considerably enhanced compared to BSPR parent compounds. While the fluorescence excitation energy of the BSPR reference compounds (370 nm) is close to the intense absorption responsible of the photochromic character (350 nm), the fluorescence excitation of the hybrid is shifted to lower energy (400 nm), improving the population of the emissive state. Combined NOESY NMR and theoretical calculations of the closed form of the hybrid give an intimate understanding of the conformation adopted by the hybrid and show that the nitroaryl moieties of the BSPR is folded toward the POM, which should affect the electronic properties of the BSPR.

12.
Chem Rec ; 17(2): 250-266, 2017 02.
Artigo em Inglês | MEDLINE | ID: mdl-27546462

RESUMO

Post-functionalization of organically modified polyoxometalates (POMs) is a powerful synthetic tool to devise functional building blocks for the rational elaboration of POM-based molecular materials. In this personal account we focus on iodoaryl-terminated POM platforms, describe reliable routes to the synthesis of covalent organic-inorganic POM-based hybrids and their integration into advanced molecular architectures or multi-scale assemblies as well as their immobilization onto surfaces. Valorisation of the remarkable redox properties of POMs in the fields of artificial synthesis and molecular electronic is especially considered.

13.
Dalton Trans ; 45(42): 16653-16660, 2016 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-27778004

RESUMO

Polyoxometalate (POM) chemistry has recently offered excellent examples of single ion magnets (SIMs) and molecular spin qubits. Compared with conventional coordination compounds, POMs provide rigid and highly symmetric coordination sites. However, all POM-based SIMs reported to date exhibit a very limited range of possibilities for chemical processability. We present herein two new families of POM-based SIMs which are soluble in organic solvents: [Ln(ß-Mo8O26)2]5- {LnIII = Tb, Dy, Ho, Er, Tm and Yb} and the functionalised POMs [Ln{Mo5O13(OMe)4NNC6H4-p-NO2}2]3- {LnIII = Tb, Dy, Ho, Er, Yb and Nd}. In addition, these two families represent the first SIMs based on polyoxomolybdates. A magneto-structural analysis of these families is presented, which is based on an effective crystal field model, and compared with the results reported in analogous lanthanoid SIMs based on polyoxotungstates.

14.
Inorg Chem ; 55(14): 6929-37, 2016 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-27351596

RESUMO

The polyoxomolybdate hybrid TBA3[PMo11O39{Sn(C6H4)C≡C(C6H4)N2}] K(Mo)Sn[N2(+)] was prepared through Sonogashira-type coupling between TBA4[PMo11O39{Sn(C6H4)I}] K(Mo)Sn[I] and an excess of 3,3-diethyl-1-(4-ethynylphenyl)triaz-1-ene bearing a protected diazonium function, followed by its deprotection by the addition of trifluoroacetic acid (TFA). This enlarges the family of organic-inorganic polyoxomolybdate-based hybrids, which has been far less investigated than their related polyoxotungstates. The diazonium function allows for the electrochemical grafting on glassy carbon, and the K(Mo)Sn-modified electrode was further probed by cyclic voltammetry. The PMo11Sn core was found to be highly sensitive to protonation, and five bielectronic proton-coupled electron transfer processes were detected in the presence of an excess of TFA, thus corresponding to the injection of up to 10 electrons in the potential range between 0.15 and -0.45 V/SCE. The gain observed in the thermodynamic potentials is however detrimental to the apparent kinetics of the electron transfer, which drops from 500 s(-1) in the absence of acid to 12 s(-1) in the presence of an excess of TFA.

15.
Langmuir ; 32(19): 4774-83, 2016 05 17.
Artigo em Inglês | MEDLINE | ID: mdl-27118296

RESUMO

The interfacing of polyoxometalates and graphene can be considered to be an innovative way to generate hybrid structures that take advantage of the properties of both components. Polyoxometalates are redox-sensitive and photosensitive compounds with high temperature stability (up to 400 °C for some), showing tunable properties depending on the metal incorporated inside the complex. Graphene has a unique electronic band structure combined with good material properties for electrical and optical applications. The spontaneous, rather than electrochemical, functionalization of epitaxial graphene on SiC with Keggin phosphomolybdate derivative TBA3[PMo11O39{Sn(C6H4)C≡C(C6H4)N2}] (named K(Mo)Sn[N2(+)]) bearing a phenyl diazonium unit is investigated. Graphene decoration is evidenced by means of AFM, Raman, XPS, and cyclic voltammetry, indicating a successful immobilization of the polyoxomolybdate. The covalent bonding of the polyoxometalate to the graphene substrate can be deduced from the appearance of a D band in the Raman spectra and from the loss of mobility in the electrical conduction. High-resolution XPS spectra reveal an electron transfer from the graphene to the Mo complex. The comparison of charge-carrier density measurements before and after grafting supports the p-type doping effect, which is further evidenced by work function UPS measurements.

16.
J Am Chem Soc ; 138(15): 5093-9, 2016 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-27019075

RESUMO

The metal-driven self-assembly processes of a covalent polyoxometalate (POM)-based hybrid bearing remote terpyridine binding sites have been investigated. In a strongly dissociating solvent, a discrete metallomacrocycle, described as a molecular triangle, is formed and characterized by 2D diffusion NMR spectroscopy (DOSY), small-angle X-ray scattering (SAXS), and molecular modeling. In a less dissociating solvent, the primary supramolecular structure, combining negatively charged POMs and cationic metal linkers, further self-assemble through intermolecular electrostatic interactions in a reversible process. The resulting hierarchical assemblies are dense monodisperse nanoparticles composed of ca. 50 POMs that were characterized by SAXS and transmission electron microscopy (TEM). This multiscale organized system directed by metal coordination and electrostatic interactions constitutes a promising step for the future design of POM self-assemblies with controllable structure-directing factors.

17.
Small ; 12(2): 220-8, 2016 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-26578032

RESUMO

In the present article, the successful coassembly of spherical 6.2 nm maghemite (γ-Fe2O3) nanocrystals and giant polyoxometalates (POMs) such as 2.9 nm {Mo132} is demonstrated. To do so, colloidal solutions of oleic acid-capped γ-Fe2O3 and long-chain alkylammonium-encapsulated {Mo132 } dispersed in chloroform are mixed together and supported self-organized binary superlattices are obtained upon the solvent evaporation on immersed substrates. Both electronic microscopy and small angles X-ray scattering data reveal an AB-type structure and an enhanced structuration of the magnetic nanocrystals (MNCs) assembly with POMs in octahedral interstices. Therefore, {Mo132} acts as an efficient binder constituent for improving the nanocrystals ordering in 3D films. Interestingly, in the case of didodecyldimethylammonium (C12)-encapsulated POMs, the long-range ordered binary assemblies are obtained while preserving the nanocrystals magnetic properties due to weak POMs-MNCs interactions. On the other hand, POMs of larger effective diameter can be employed as spacer blocks for MNCs as shown by using {Mo132} capped with dioctadecyldimethylammonium (C18) displaying longer chains. In that case, it is shown that POMs can also be used for fine-tuning the dipolar interactions in γ-Fe2O3 nanocrystal assemblies.

18.
Chemistry ; 21(52): 19010-5, 2015 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-26602994

RESUMO

A polyoxometalate-based molecular triangle has been synthesized through the metal-driven self-assembly of covalent organic/inorganic hybrid oxo-clusters with remote pyridyl binding sites. The new metallomacrocycle was unambiguously characterized by using a combination of (1)H NMR spectroscopy, 2D diffusion NMR spectroscopy (DOSY), electrospray ionization travelling wave ion mobility mass spectrometry (ESI-TWIM-MS), small-angle X-ray scattering (SAXS) and molecular modelling. The collision cross-sections obtained from TWIM-MS and the hydrodynamic radii derived from DOSY are in good agreement with the geometry-optimized structures obtained by using theoretical calculations. Furthermore, SAXS was successfully employed and proved to be a powerful technique for characterizing such large supramolecular assemblies.

19.
Inorg Chem ; 54(15): 7607-16, 2015 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-26161980

RESUMO

Polyoxometalate (POM) hybrids have been covalently immobilized through the formation of amide bonds on several types of mesoporous silica. This work allows the comparison of three POM-based mesoporous systems, obtained with three different silica supports in which either the organic functions of the support (amine vs carboxylic acid) and/or the structure of the support itself (SBA-15 vs mesocellular foams (MCF)) were varied. The resulting POM-based mesoporous systems have been studied in particular by high resolution transmission electronic microscopy (HR-TEM) in order to characterize the nanostructuration of the POMs inside the pores/cells of the different materials. We thus have shown that the best distribution and loading in POMs have been reached with SBA-15 functionalized with aminopropyl groups. In this case, the formation of amide bonds in the materials has led to the nonaggregation of the POMs inside the channels of the SBA-15. The catalytic activity of the anchored systems has been evaluated through the epoxidation of cyclooctene and cyclohexene with H2O2 in acetonitrile. The reactivity of the different grafted POMs hybrids has been compared to that in solution (homogeneous conditions). Parallels can be drawn between the distribution of the POMs and the activity of the supported systems. Furthermore, recycling tests together with catalyst filtration experiments during the reaction allowed us to preclude the hypothesis of a significant leaching of the supported catalyst.

20.
J Phys Chem B ; 119(20): 6326-37, 2015 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-25937090

RESUMO

We easily produced a series of polyoxometalate (POM) nanoparticles by taking benefit from electrostatic attractions between various POMs and alkylammonium cations. These self-assembled supramolecular nanoparticles are fully characterized in terms of shape, nanostructure, and physicochemical properties. The nanoparticle differences are discussed on the basis of the chemical composition of the initial POM. Moreover, such particles have the ability to stabilize water-in-oil Pickering emulsions. Using a gel-trapping technique coupled to atomic force microscopy (AFM) observations, we determined their affinity toward oil by the contact angle of adsorbed nanoparticles. We show that the emulsion droplet size and stability can be directly linked to the nanoparticle hydrophobicity, which is tuned by the charge localization and molecular packing of POMs with the ammonium cations. Such particles are of special interest as they open large possibilities for Pickering interfacial catalysis.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA