Complex molecular assemblies

In the framework of our research activities in inorganic molecular chemistry, the synthesis of new chemical objects remains the core of the scientific activities of the whole E-POM group. These activities require the design of custom-made systems, generally via a bottom-up approach. Beyond the functionalization techniques developed in the group for more than 20 years, our synthetic arsenal also includes the post-modification of useful functions pre-incorporated in elementary building blocks. This approach can be applied to the development of very different systems: polyoxometallates (S. Renaudineau), hybrid polyoxometallates, hetero-poly-metallic complexes (V. Marvaud), supramolecular assemblies (G. Izzet), planar surfaces (A. Proust, F. Volatron) or modified mesoporous surfaces (R. Villanneau). The coordination properties of molecular building blocks towards cations with additional properties are also studied (G. Guillemot, V. Marvaud). The POMs/nanoparticles association is also exploited (R. Villanneau, F. Volatron ).
The interaction and modulation of amyloid peptide aggregation by POMs is studied in order to understand the supramolecular interactions leading to the regulation of the aggregation of intrinsically disordered proteins, involved in a number of pathologies (Alzheimer’s disease, type B diabetes,…) (S. Blanchard ).

Keywords: chemistry/functionalization of polyoxometallates, coordination assemblies, liquid crystals, supramolecular gels, hetero-poly-metallic complexes, dendrimers, aggregation of amyloid peptides

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

M. Laurans, M. Mattera, R. Salles, L. K’Bidi, P. Gouzerh, S. Renaudineau, F. Volatron, G. Guillemot, S. Blanchard, G. Izzet, A. Solé-Daura,* J. M. Poblet, and A. Proust*, Inorg. Chem. 2022, 61, 7700−7709

The mixed Mo/W Kegging-type polyoxometalate hybrid (TBA)4[PW9Mo2O39Sn(C6H4I)] has been prepared by reaction between [?-PW9Mo2O39]7- and [Cl3Sn(C6H4I)] in dried acetonitrile, in the presence of tetra-n-butylammonium bromide. Further coupling reaction affords the ferrocenyl derivative (TBA)4[PW9Mo2O39Sn(C6H4)C≡C(C6H4)Fc]. The POM hybrids have been thoroughly characterized by NMR and IR spectroscopies. The electrochemical analysis confirms their ease of reduction when compared to the all-tungsten analog, albeit with a second reduction process occurring at a lower potential than in the all-molybdenum species. It is noteworthy that the second reduction is accompanied by an unusual red-shift of the electronic absorption spectrum. Whereas there is no doubt that the first reduction deals with molybdenum, the location of the second electron in the bi-reduced species, on the second molybdenum or on tungsten, has thus been the subject of a cross-investigation by spectro-electrochemistry, ESR and theoretical calculations. Finally, it came out that the second reduction is also molybdenum-centered with two unpaired and antiferromagnetically coupled extra electrons.

Photoactive Organic/Inorganic Hybrid Materials with Nanosegregated Donor–Acceptor Arrays

Zhu, X.; Hessin, C.; Salamé, A.; Sosa-Vargas, L.; Kreher, D.; Adachi, C.; Proust, A.; Mialane, P.; Marrot, J.; Bouchet, A.; Sliwa, M.; Méry, S.; Heinrich, B.; Mathevet, F.; Izzet., G.; Angew. Chem. Int. Ed. 2021, 60, 8419–8424.

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)thienothio- phene organic donors alternate regularly. Noticeably, the sub- unit organizations in the composite are similar to that observed for the individual POM and organic donor precursors. Photo- physical studies show that in the hybrid, the fluorescence of the organic donor unit is considerably quenched both in solution and in the solid state, which is attributed to occurrence of intramolecular charge-separated state.

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

Segado Centellas, M. ; Piot, M. ; Salles, R. ; Proust, A. ; Tortech, L. ; Brouri, D. ; Hupin, S. ; Abécassis, B. ; Landy, D. ; Bo, C. ; Izzet, G., Chem. Sci. 2020, 11, 11072–11080

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. The experimental findings were corroborated with a computational investigation combining DFT and molecular dynamics simulation methods, which outlines the importance of solvation of the counter ion and POM/counter ion association in the aggregation process. The dumbbell-like species can also form gels, in the presence of a poorer solvent, displaying similar nanoorganization of the aggregates. We show that starting from the designed molecular building units whose internal charges can be controlled by redox trigger we can achieve their implementation into soft nanostructured materials through the control of their supramolecular organization.

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

Salles, R. ; Abécassis, B. ; Derat, E. ; Brouri, D. ; Bernard, A. ; Zhang, Q. ; Proust, A. ; Desmarets, C. ; Izzet, G. Inorg. Chem. 2020, 59, 4, 2458–2463

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.

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

T. Zhang, A. Solé-Daura, S. Hostachy, S. Blanchard, C. Paris, Y. Li, J. J. Carbó, J.-M. Poblet, A. Proust and G. Guillemot J. Am. Chem. Soc. 2018, 140, 14912-14923.

The silanol decorated polyoxotungstate [SbW9O33(tBuSiOH)3]3- has the ability to stabilize a low-valent d2-vanadium(III) ion in an unusual trigonal coordination environment. Indeed, [SbW9O33(tBuSiO)3V(thf)]3− (1)proves to be a unique model for a reduced vanadium atom dispersed on silica or anatase surfaces, ((≡Si–O)3VIII(OH2)) (M= Si or Ti). Such V(III) entity has been proposed as an intermediate in a Mars-van Krevelen type of mechanism for partial oxidation of light alcohols. When exposed to air, compound 1 is readily oxidized to the V(V)-oxo derivative [SbW9O33(tBuSiO)3VO]3− (2). Beyond the structural model aspect, we introduce in this work one fascinating facet of the polyoxotungstate-based ligand [SbW9O33(tBuSiOH)3]3− which is its ability to act as a multi-electron acceptor. At variance with reported organic models, polyoxometalates are redox non-innocent ligands, which increases the complexity and thus potentialities of the resulting functional models. Hence, in compound 1 the d2–electrons are localized in degenerated d(V) orbitals whereas in the electronically analogous bireduced [SbW9O33(tBuSiO)3VO]5− (3) one electron is localized on d(V) orbital and the second one is delocalized on the polyoxotungstic framework. This is a unique example of a polyoxometalate derivative with decoupled V(IV) and W(V) centers.

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

M. Piot, B. Abécassis, D. Brouri, C. Troufflard, A. Proust, G. Izzet, Proc. Natl. Acad. Sci. U. S. A. 2018, 36, 8895-8900.

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.

Charge Effect on the Formation of Polyoxometalate-Based Supramolecular Polygons Driven by Metal Coordination

M. Piot, S. Hupin, H. Lavanant, C. Afonso, L. Bouteiller, A. Proust, G. Izzet, Inorg. Chem., 2017, 56, 8490-8496.

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.

Tailor–made Covalent Organic-Inorganic Polyoxometalate Hybrids : Versatile Platforms for the Elaboration of Functional Molecular Architectures

G. Izzet, F. Volatron, A. Proust, Chem. Rec., 2017, 17, 250 – 266.

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.

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, 138, 5093−5099.

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. 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.