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Accueil > Les équipes > Edifices PolyMétalliques (E-POM) > Thèmes de recherche

1. Molecular inorganic synthesis

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In the frame of our research activities based on molecular inorganic chemistry, the synthesis of new chemical objects remains the core of the activities in the E-POM group. This requires the conception of tailor-made systems, via a bottom-up approach. Beyond the functionalization techniques developed in the group in the past decades, our synthetic arsenal includes also the post-modification of useful functions pre-incorporated in elementary molecular bricks. This approach can be applied to the development of very different systems, such as functionalized POMs, porous nanocapsules of the Keplerate type (in collaboration with Prof. A. Müller, University of Bielefeld), hetero-poly-metallic complexes and poly-functional architectures, the formation of extended supramolecular assemblies or the covalent grafting of molecules onto planar or mesoporous supports. The coordination properties of the aforementioned bricks toward cations of interest (in the fields of muti-functional systems or catalysis) are also studied, including their use for the generation/stabilization of metallic nanoparticles.

Keywords : native POMs- Keplerate chemistry, POM functionalization/postfunctionalization,
self-assemblies, coordination assemblies, hetero-poly-metallic complexes, dendrimers

- Hierarchical Self-Assembly of Polyoxometalate-Based Hybrids Driven by Metal Coordination and Electrostatic Interactions : From Discrete Supramolecular Species to Dense Monodisperse Nanoparticles
G. Izzet, B. Abécassis, D. Brouri, M. Piot, B. Matt, S. A. Serapian, C. Bo, A. Proust, J. Am. Chem. Soc. 2016, DOI : 10.1021/jacs.6b00972.

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.

Metal-Directed Self-Assembly of a Polyoxometalate-Based Molecular Triangle : Using Powerful Analytical Tools to Probe the Chemical Structure of Complex Supramolecular Assemblies.
G. Izzet, A. Macdonell, C. Rinfray, M. Piot, S. Renaudineau, E. Derat, B. Abécassis, C. Afonso, A ; Proust, Chem. Eur. J. 2015, 21, 19010–19015.

Precise triangulation. A combination of 1H NMR, 2D diffusion NMR spectroscopy, electrospray ionization travelling wave ion-mobility mass spectrometry, small-angle X-ray scattering, and molecular modelling allowed the unambiguous characterization of an original covalent polyoxometalate-based molecular triangle.

- A new family of hetero-tri-metallic complexes [M(CuTb)]n (n = 1, 2, ∞ ; M = Co, Cr, Fe) : synthesis, structure and tailored single-molecule magnet behavior.
N. Bridonneau, G. Gontard, V. Marvaud, Dalton Trans., 2015, 44, 5170-5178.

A new family of hetero-tri-metallic complexes [M(CuTb)]n (M(III) = Co, Cr, Fe ; n = 1, 2, ∞), composed of three series of three compounds (oligo- and poly-nuclear complexes based on [Cu-Tb] subunits), is presented and fully characterized. These nine compounds, viewed as different assemblies of single-molecule magnet (SMM) building blocks, connected to various hexacyanometalate centers, illustrate how the SMM behavior of the [CuTb] moiety can be modulated via the control of intermolecular interactions. Specifically, the combination of the "non-innocent" diamagnetic [Co(III)(CN)6](3-) center with a [Cu-Tb](3+) moiety enabled isolation of the magnetic entities, resulting in an improvement of the SMM behavior (ranging from Ueff = 5-7 cm(-1) to 15-17 cm(-1)).

- A covalent polyoxomolybdate-based hybrid with remarkable electron reservoir properties
C. Rinfray, S. Renaudineau, G. Izzet, A. Proust, Chem.Commun.,2014,50,8575—8577

A new polyoxomolybdate-based hybrid platform TBA4[PMo11O39Sn(p-C6H4I)] is reported. The presence of a post-functionalisable iodo-aryl moiety allows the grafting of a ferrocenyl moiety onto the POM. The electrochemical characterisation shows the effect of molybdenum on the electron reservoir properties of POM-based hybrids, which are further enhanced upon the addition of an acid.

- Simple procedure for vacant POMs-stabilized palladium(0) nanoparticles in water : structural and dispersive effects of lacunary polyoxometalates
R. Villanneau, A. Roucoux, P. Beaunier, D. Brouri, A. Proust, R.S.C. Adv., 2014, 4, 26491-26498.

Metallic palladium nanoparticles have been generated by hydrogenation with H2 of solutions of several non organometallic PdII-derivatives of heteropolytungstates, at ambient temperature and atmospheric pressure. These nanoparticles have been characterized by various techniques : 31P NMR and Raman spectroscopy, TEM (including cryogenic techniques), DLS, EDX and XPS. The present strategy ruled out the presence of other ligands and/or stabilizing agents other than the lacunary polyoxometalates (POMs) used. This allows the evaluation of the true efficiency of the different vacant POMs for the stabilization of the nanoparticles.

- Versatile Post-Functionalization of Polyoxometalate Platforms via Unprecedented Scope of Palladium-Catalyzed Coupling Reactions
M. M. Lorion, B. Matt, S. Alves, A. Proust, G. Poli, J. Oble, G. Izzet, Chem. Eur. J., 2013, 19, 12607 – 12612.

Handy POMs. Different palladium-catalyzed coupling reactions have been applied for the first time to polyoxometalate post-functionalization. As a proof of concept, we investigated the feasibility of each reaction with one model substrate and optimized each synthetic condition to obtain full conversions and high purity hybrid compounds. This study widens the scope of the post-functionalization routes in polyoxometalate chemistry.

- Bisorganophosphonyl and -Organoarsenyl Derivatives of Heteropolytungstates as Hard Ligands for Early-Transition-Metal and Lanthanide Cations
R. Villanneau, A. Ben Djamaa, L.-M. Chamoreau, G. Gontard, A. Proust, Eur. J. Inorg. Chem., 2013, 1815-1820.

The coordination properties of polyoxometalate (POM) hybrids that incorporate organophosphonyl or -arsenyl functions were studied toward cations from different families of the periodic table (La3+, Ca2+, V5+, Ti4+). The structures of all complexes were determined by single-crystal X-ray diffraction and showed evidence for the particular hardness of the coordination sites in these POM hybrids.

- Cyclodextrin-Induced Auto-healing of Hybrid Polyoxometalates.
G. Izzet, M. Ménand, M., B. Matt, S. Renaudineau, L.-M. Chamoreau, M. Sollogoub, A. Proust, Angew. Chem. Int. Ed., 2012, 51, 487-490, Hot Paper

You’ll never walk alone. An auto-healing process of the first host–guest complex involving a polyoxometalate hybrid and a cyclodextrin is reported. Indeed, this inclusion complex allows the complete restoration of the anchored organic moiety released by a basic stress, a process otherwise not fully reversible.
-  Functionalization and post-functionalization a step towards polyoxometalate-based materials.
A. Proust, B. Matt, R. Villanneau, G. Guillemot, P. Gouzerh, G. Izzet, Chem. Soc. Rev., 41, 7605–7622. Themed issue on Polyoxometalates.

Polyoxometalates (POMs) have remarkable properties and a great deal of potential to meet contemporary societal demands regarding health, environment, energy and information technologies. However, implementation of POMs in various functional architectures, devices or materials requires a processing step. Most developments have considered the exchange of POM counterions in an electrostatically driven approach : immobilization of POMs on electrodes and other surfaces including oxides, embedding in polymers, incorporation into Layer-by-Layer assemblies or Langmuir–Blodgett films and hierarchical self-assembly of surfactant-encapsulated POMs have thus been thoroughly investigated. Meanwhile, the field of organic–inorganic POM hybrids has expanded and offers the opportunity to explore the covalent approach for the organization or immobilization of POMs. In this critical review, we focus on the use of POM hybrids in selected fields of applications such as catalysis, energy conversion and molecular nanosciences and we endeavor to discuss the impact of the covalent approach compared to the electrostatic one. The synthesis of organic–inorganic POM hybrids starting from bare POMs, that is the direct functionalization of POMs, is well documented and reliable and efficient synthetic procedures are available. However, as the complexity of the targeted functional system increases a multi-step strategy relying on the post-functionalization of preformed hybrid POM platforms could prove more appealing. In the second part of this review, we thus survey the synthetic methodologies of post-functionalization of POMs and critically discuss the opportunities it offers compared to direct functionalization.

- From linking of metal-oxide building blocks in a dynamic library to giant clusters with unique properties and towards adaptive chemistry
A. Müller, P. Gouzerh, Chem. Soc. Rev., 2012, 41, 7431-7463.

The porous sphere- and ring-shaped polyoxometalate-type nano-objects with unique properties offer the option for the investigation of a variety of phenomena of interdisciplinary interest including those under confined conditions, for instance related to fundamental aspects of the hydrophobic effect.

-  Spontaneous self-assembly of a giant spherical metal-oxide Keplerate : addition of one building block induces “immediate” formation of the complementary one from a constitutional dynamic library
C. Schäffer, A. M. Todea, P. Gouzerh, A. Müller, Chem. Commun., 2012, 48, 350-352.

A giant molecular molybdenum-oxide spontaneously assembles from two bricks : the second is formed by addition of the first to a dynamic library.

- Softening of pore and interior properties of a metal-oxide-based capsule : substituting 60 oxide by 60 sulfide ligands
C. Schäffer, A. M. Todea, H. Bögge, E. Cadot, P. Gouzerh, S. Kopilevich, I. A. Weinstock, A. Müller, Angew. Chem. Int. Ed., 2011, 50, 12326–12329.

A hard capsule gets soft : The exchange of 60 oxide by 60 sulfide ligands in a well-known porous metal-oxide capsule skeleton containing 132 metal atoms changes the interior properties as well as pore sizes, reactivities, flexibilities and affinities to guest molecules.

- Insights into the Coordination Chemistry of Phosphonate Derivatives of Heteropolytungstates
R. Villanneau, D. Racimor, E. Messner-henning, H. Rousselière, S. Picart, R. Thouvenot, A. Proust, Inorg. Chem., 2011, 50, 1164-1166.

The coordination properties of vacant bis-phosphonate derivatives of polyoxometalates, with easily tunable functions, have been explored. Preparation and crystallographic structure of their La3+ and Zr4+ complexes are described herein.

- Unprecedented and Differently Applicable Pentagonal Units in a Dynamic Library : A Keplerate of the Type {(W)W5}12{Mo2}30
C. Schäffer, A. Merca, H. Bögge, A. M. Todea, M. L. Kistler, T. Liu, R. Thouvenot, P. Gouzerh, A. Müller, Angew. Chem. Int. Ed., 2009, 149-153.

Magic pentagons. Exploitation of versatile pentagonal units/ligands has previously led to giant molybdenum oxide based curved species, including spherical Keplerates. Similar methodology is now also applicable to the related tungstate scenario (see corresponding basic central pentagonal unit in green).

- Palladium(II)-Phosphotungstate Derivatives : Synthesis and Characterization of the [Pdx{WO(H2O)}3-x{A,α-PW9O34}2](6+2x)- Anions
R. Villanneau, S. Renaudineau, P. Herson, K. Boubekeur, R. Thouvenot, A. Proust, Eur. J. Inorg. Chem., 2009, 479-488.

A series of PdII derivatives of the [P2W21O71(H2O)3]6- heteropolytungstate with general formula [Pdx{WO(H2O)}3-x{A,α-PW9O34}2](6+2x)- (x = 1-3) have been obtained by reaction between palladium nitrate and [P2W20O70(H2O)2]10-, [P2W19O69(H2O)2]14- and [PW9O34]9- respectively. The crystallographic structure of K10[Pd2{WO(H2O)}{A,α-PW9O34}2]•30H2O has been reported.

- Photochemical activation of an azido manganese-monosubstituted Keggin polyoxometalate : on the road to a Mn(V)-nitrido derivative
G. Izzet, E. Ishow, J. Delaire, C. Afonso, J.-C. Tabet, A. Proust, Inorg. Chem., 2009, 48, 11865–11870.

The manganese(V)-nitrido polyoxometalate derivative [PW11O39{MnVN}]5- has been synthesized by photochemical activation of the parent manganese(III)-azido derivative [PW11O39MnIIIN3]5-. The photoactivation proceeds through two competitive routes, yielding to the targeted product of photooxidation {MnVN} or the undesirable product of photoreduction {MnIIL} (L = H2O, N3) depending on the photolysis conditions. A simplified photolysis mechanism involving two different excited states was proposed to account for the temperature and wavelength dependence.