Sébastien Floquet

Molecular weights of cyclic and hollow clusters measured by DOSY NMR spectroscopy.

The Stokes-Einstein expression of the diffusion coefficient as a function of the hydrodynamic radius of the diffusing object does not explicitly carry the mass dependency of the object. It is possible to correlate the translational self-diffusion coefficients D with the molecular weight M for an ensemble of cyclic or hollow clusters ranging from about 200 to 30,000 g x mol(-1). From this correlation, the mass of a cluster can be deduced from its diffusion coefficient. Consistency of diffusion as a power law of mass and Stokes-Einstein formulation is completely fulfilled with the selected compounds of this contribution.

Monometallic lanthanide complexes with tridentate 2,6-dicarboxamidopyridine ligands. Influence of peripheral substitutions on steric congestion and antenna effect

The systematic investigation of steric and electronic effects on the formation of lanthanide complexes with the tridentate N,N,N′,N′-tetraalkylpyridine-2,6-dicarboxamide ONO ligands (alkyl = ethyl: L5, isopropyl: L6 and benzyl: L7) shows a reduced affinity with increasing steric demand in the order L5 < L6 < L7. [Ln(Li)]3+ and [Ln(Li)2]3+ are formed with the three ligands, but 1 ∶ 3 complexes are strictly limited to [Ln(L5)3]3+ and [Ln(L6)3]3+ because of the significant steric congestion provided by the twelve benzyl groups located along the three-fold axis in [Ln(L7)3]3+. Comparisons between L6 and L7 in the 1 ∶ 2 complexes evidence superimposable pseudo-monocapped square antiprismatic coordination spheres in the crystal structures of [Ln(Li)2(H2O)2(CF3SO3)](CF3SO3)2 (i = 6, Ln = Eu: 9; i = 7, Ln = Gd: 10). Photophysical properties of [Ln(L6)2]3+ and [Ln(L7)2]3+ (Ln = Eu, Gd, Tb, Lu) are similar except for improved quantum yields for [Ln(L7)2]3+ (Ln = Eu, Tb) which can be assigned to a slightly more efficient L7 → LnIII energy transfer process. The removal of two benzyl groups in the analogous N,N′-dibenzylpyridine-2,6-dicarboxamide ligand (L8) restores the formation of stable triple-helical complexes as demonstrated by the crystal structure of [Tb(L8)3]2(CF3SO3)6 (11). However, the existence of intricate mixtures of isomers in solution which are blocked on the NMR time scale limits their use as building blocks for the design of polymetallic d–f and f–f helicates.

Cubic Box versus Spheroidal Capsule Built from Defect and Intact Pentagonal Units

The high-nuclearity polyoxothiomolybdate [H(8)Mo(84)S(48)O(188)(H(2)O)(12)(CH(3)COO)(24)](32-) has been prepared and characterized by single-crystal X-ray crystallography and (1)H NMR, IR, Raman, and UV-vis spectroscopy. The solid-state structure reveals an unprecedented and intriguing arrangement consisting of a nanoscaled anionic cube. The surprisingly open structure of this {Mo(84)}-type cubic box features a large inner void that is accessible via its six open square faces with diameters of ca. 9 Å. Importantly, this molecular system appears to be highly functionalizable because of the presence of 24 exposed exchangeable acetate ligands.

Evidence of ionic liquid crystal properties for a DODA+ salt of the keplerate [Mo132O372(CH3COO)30(H2O)72]42−

Thermal studies of a DODA+ salt of the nanoscopic hollow sphere [Mo132O372(H2O)72(CH3CO2)30]42− revealed ionic liquid crystalline properties, which were evidenced by Polarised Optical Microscopy, DSC and SA-XRD.

One-step synthesis and stabilization of gold nanoparticles in water with the simple oxothiometalate Na2[Mo3(μ3-S)(μ-S)3(Hnta)3]

Na2[Mo3(μ3-S)(μ-S)3(Hnta)3] serves both as a reducing and a capping agent in the synthesis of Au nanoparticles in water at room temperature in a “fully green chemistry-type process”, thus avoiding the usual two-step preparation of thiolate-monolayer-coated gold nanoparticles. The nanoparticles were characterized by TEM, DLS, UV-vis spectroscopy, XPS and XRD analyses and cyclic voltammetry.

Capture of the Complex [Ni(dto)2]2– (dto2– = Dithiooxalato Ligand) in a Mo12 Ring: Synthesis, Characterizations, and Application toward the Reduction of Protons

The encapsulation of the complex [Ni(dto)(2)](2-) within an oxothiododecamolybdic cyclic cluster has been investigated. The resulting molybdenum ring, [Mo(12)O(12)S(12)(OH)(12)(Ni(dto)(2))](2-), corresponds to the first example of the {Mo(2)O(2)S(2)}-based assembly arranged around a 3d transition-metal complex. It was unambiguously characterized in the solid state and in solution by FT-IR spectroscopy, single-crystal X-ray diffraction, NMR, UV-visible spectroscopy, and electrospray ionization-high-resolution mass spectrometry (ESI-HRMS). The latter technique revealed to be a powerful tool for the characterization of templated molybdenum ring systems in solution and gave excellent results in high resolution. The electronic spectrum of [Mo(12)O(12)S(12)(OH)(12)(Ni(dto)(2))](2-) evidenced a strong red shift of the LMCT bands attributed to the complex [Ni(dto)(2)](2-), suggesting significant variations of the electronic properties upon its encapsulation within the Mo(12) ring. These differences were demonstrated by electrochemical studies in CH(3)CN, which also revealed, for both compounds [Ni(dto)(2)](2-) and [Mo(12)O(12)S(12)(OH)(12)(Ni(dto)(2))](2-), electrocatalytic properties for the reduction of protons. These results evidence the ability of dithioxalato complexes to act as electrocatalysts for the hydrogen evolution reaction (HER) and confirm such a property for oxothiomolybdenum rings.

Coordination-Induced Condensation of [Ta6O19]8–: Synthesis and Structure of [{(C6H6)Ru}2Ta6O19]4– and [{(C6H6)RuTa6O18}2(μ-O)]10−

Reaction of [(C6H6)RuCl2]2 and Na8[Ta6O19] gives two new hybrid organometallic POM complexes, Na10[{(C6H6)RuTa6O18}2(μ-O)]·39.4H2O (Na10-1) and Na4(trans-[{(C6H6)Ru}2Ta6O19]·20H2O (Na4-2). In both cases the half-sandwich fragments {(C6H6)Ru}(2+) are coordinated as additional vertices to the {Ta3(μ2-O)3} triangles of the hexatantalate. According to NMR and ESI-MS data, the dimeric complex [{(C6H6)RuTa6O18}2(μ-O)](10-) dissociates in water with the formation of monomeric [(C6H6)RuTa6O19](6-) species (1a). X-ray structural characterization and aqueous speciation of the complexes by (13)C, (1)H, and DOSY NMR; ESI-MS; and capillary electrophoresis (CE) have been carried out.

Polyoxometalate, Cationic Cluster, and γ-Cyclodextrin: From Primary Interactions to Supramolecular Hybrid Materials

Herein, we report on a three-component supramolecular hybrid system built from specific recognition processes involving a Dawson-type polyoxometalate (POM), [P2W18O62]6-, a cationic electron-rich cluster [Ta6Br12(H2O)6]2+, and γ-cyclodextrin (γ-CD). Such materials have been investigated using a bottom-up approach by studying the specific interactions between γ-CD and both types of inorganic units. Their ability to interact has been investigated in the solid state by single-crystal X-ray diffraction (XRD) and in solution using multinuclear NMR methods (including DOSY, EXSY, and COSY), electrospray ionization mass and UV-vis spectroscopies, electrochemistry, and isothermal titration calorimetry experiments. Single-crystal XRD analysis reveals that POM:γ-CD constitutes a highly versatile system which gives aggregates with 1:1, 1:2, and 1:3 stoichiometry. Surprisingly, these arrangements exhibit a common feature wherein the γ-CD moiety interacts with the Dawson-type POMs through its primary face. We present also the first structural model involving an octahedral-type metallic cluster with γ-CD. XRD study reveals that the cationic [Ta6Br12(H2O)6]2+ ion is closely embedded within two γ-CD units to give a supramolecular ditopic cation, suitable to be used as a linker within extended structure. Solution study demonstrates clearly that pre-associations exist in solution, for which binding constants and thermodynamic parameters have been determined, giving preliminary arguments about the chaotropic nature of the inorganic ions. Finally, both building blocks, i.e., the ditopic supramolecular cation {[Ta6Br12(H2O)6]@2CD}2+ and the Dawson-type anion, react together to give a three-component, well-ordered hybrid material derived either as a supramolecular hydrogel or single crystals. The solid-state structure shows an unprecedented helicoidal tubular chain resulting from the periodic alternation of POM and supramolecular cation, featuring short hydrogen-bonding contacts between the electron-poor POM and electron-rich cluster. The 1D tubular ionic polymer observed in the single crystals should make it possible to understand the long-range ordering observed within the hydrogel hybrid material. The supramolecular chemical complementarities between the γ-CD-based ditopic cation and POM open a wide scope for the design of hybrid materials that accumulate synergistic functionalities.

Biopolymer folding driven nanoparticle reorganization in bio-nanocomposites

In this paper we report the influence of biopolymer folding on nanoparticle spatial distribution in two typical bio-nanocomposite hydrogels. These systems consist of negatively charged nanosized fillers (polyoxotungstate clusters and silica particles, 2.2 nm and 23.0 nm in diameter, respectively) dispersed at low volume fractions in a positively charged gelatin hydrogel. The filler state of dispersion is investigated during triple helix folding by combining small-angle neutron scattering (SANS) and polarimetry experiments. Neutron contrast matching/polarimetry correlations indicate that the nanoparticle spatial distribution is clearly modified during triple helix folding for the two systems. In the first case, polyoxotungstate clusters are initially arranged in small finite size aggregates that grow with increasing triple helix rate: ΔRG ≈ +150% and ΔI(q → 0) ≈ +250% for Δ[helix] ≈ +40%. In the second case, silica particles initially form a connected network that undergoes a significant densification through gelatin conformational transition. In the two cases, the kinetics of triple helix folding is only slightly affected by the presence of the nanoparticles and their state of dispersion. In our experimental conditions, these two processes are almost thermo-reversible following triple helix unfolding.

A New Oxomolybdate Component Extracted from the Virtual Dynamic Library Yielding the Macrocyclic Anion [(MoVI8O28)4(MoV2O2S2)4]24-

A rare isomer of the {Mo(8)O(28)}(8-) anion has been trapped from an acidified aqueous solution of molybdate by using the {Mo(2)O(2)S(2)}(2+) oxothio cation as the linker and isolated as a part of a unique macrocyclic anion, which consists of four isopolyoxomolybdate fragments {Mo(8)O(28)} bridged by four {Mo(2)O(2)S(2)} units.