Corine Simonnet-Jégat

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.

Selective Inclusion of Cu+ and Ag+ Electron-Rich Metallic Cations within Supramolecular Polyoxometalates Based on {AsW9O33}{Mo3S4} Combinations

Coordination of the [Mo(3)S(4)(H(2)O)(9)](4+) cluster with the trivacant [AsW(9)O(33)](9-) ion gives the supramolecular complex [{(H(4)AsW(9)O(33))(4)(Mo(3)S(4){H(2)O}(5))}(2)](12-) (1) in good yield. The structure of 1 shows that two [H(4)AsW(9)O(33)](5-) subunits sandwich a single central [Mo(3)S(4)(H(2)O)(5)](4+) ion to give a basic monomeric unit [(H(4)AsW(9)O(33))(2){Mo(3)S(4)(H(2)O)(5)}](6-). In the solid state, a supramolecular dimeric association is evidenced that consists of two [(H(4)AsW(9)O(33))(2){Mo(3)S(4)(H(2)O)(5)}](6-) units held together by twelve hydrogen bonds and four SS contacts. Complex 1 reacts with NaAsO(2), AgNO(3) and CuI to give compounds 2, 3 and 4, respectively. X-ray structural analysis reveals that the molecular arrangements of 2 to 4 are closely related to the parent structure of 1. {AsOH}(2+), Ag(+) and Cu(+) ions are located on three distinct pairs of sites. Two hanging {AsOH}(2+) groups in 2 are symmetrically attached to two opposite {AsW(9)O(33)} subunits. Complex 3 is the first example of an Ag/{Mo(3)S(4)} combination in which the environment of the two equivalent Ag(+) cations is remarkable for containing two sulfur atoms belonging to {Mo(3)S(4)}, two oxygen and one central arsenic atom of the {AsW(9)O(33)} subunits. Potentiometric titration shows that the addition of Ag(+) ions is quantitative and occurs in two successive steps (K(1)=4.1 x 10(6) and K(2)=2.3 x 10(5) L mol(-1)), which is consistent with the retention of the supramolecular cluster in solution. The structure of 4 reveals a single copper atom embedded in the central part of the dimer. The Cu(+) cation is bound to four sulfur atoms to complete a cuboidal moiety. UV/Vis studies in solution indicate that the stability of the dimeric assemblies of 2, 3 and 4 is significantly enhanced by the presence of Cu(+) or Ag(+) ions, which act as additional coordination linkers within the supramolecular cluster. The anions 1 to 4 were characterised by (183)W NMR spectroscopy in solution. The 10-line spectra recorded for each of them are consistent with an averaged C(2h) molecular symmetry in solution.

Nanocomposite systems based on gold nanoparticles and thiometalates. From colloids to networks

A new nanocomposite system based on gold nanoparticles and thiometalates is described. According to the metalate species, WS42¬ or WS2O22¬, and to the experimental conditions, two sizes of particles are obtained (d = 2 or 5 nm). These particles lead either to stable colloidal solutions or irreversible micrometric spherical aggregates of nanoparticles cemented by WS42¬. Energy dispersive spectrometry (EDS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS) have been used to fully characterize the different composite systems.

Photochemical in situ elaboration of polyoxometalate (α-[SiMo12O40]4−)/polymer hybrid materials

α-Silicon polyoxomolybdates in combination with an iodonium salt and/or a silane are used to generate phenyl and/or silyl radicals as well as silylium cations upon UV light irradiation. These species can initiate the radical photopolymerization of acrylates, the cationic photopolymerization of epoxides and the photopolymerization of epoxy/acrylate blends (i.e. for the synthesis of interpenetrated polymer networks) thereby leading to the formation of polyoxometalate/polymer hybrid materials. The mechanical properties of e.g. the polyether films are affected by the presence of polyoxometalate in the matrix as shown by their dynamic mechanical analysis (DMA). The photochemical mechanisms are studied by steady state photolysis, cyclic voltammetry, and electron spin resonance techniques.

Interfacing a heteropolytungstate complex and gelatin through a coacervation process: design of bionanocomposite films as novel electrocatalysts

Bionanocomposite films on glassy carbon electrodes (GCEs) have been prepared by a very straightforward and reliable method based on a layer-by-layer deposition of polyoxometalate (POM) (i.e. [BW12O40]5−) and gelatin solutions. The strong immobilisation of [BW12O40]5− on the surface of the GCE results from electrostatic interactions between gelatin and POM, as evidenced in a hybrid hydrogel prepared by a coacervation process. The GCE has also been modified by imidazolium based ionic liquids in order to increase the charge transfer rate. Two modified electrodes with one or two POM layers have been prepared by this strategy. When compared to other POM-based modified electrodes, the novel electrodes with two POM layers exhibit excellent electrocatalytic performance for nitrite detection at pH 3 in terms of sensitivity (868 mA M−1 cm−2) and linear range of nitrite concentrations (50–600 μM).

A general route to nanostructured M[V3O8] and Mx[V6O16] (x = 1 and 2) and their first evaluation for building enzymatic biosensors

In order to develop novel electroactive hosts for biosensor design, the possibility to use nanostructured vanadate phases as alternatives to well-known V2O5 gels was studied. For this purpose, the formation of M[V3O8] and Mx[V6O16] (x = 1 and 2) oxides by the sol–gel process has been studied over a wide range of cations (M+ = Li+, Na+, K+, Cs+, and NH4+; M2+ = Ca2+, Mg2+ and Ba2+). By a combination of XRD, 51V NMR and SEM studies, it was possible to evidence the influence of the nature and hydration state of cations on the size and morphology of the resulting particles as well as on the kinetics of their formation. On this basis, K2[V6O16] was evaluated for glucose oxidase encapsulation, either via impregnation or co-precipitation methods. When compared to V2O5, these novel bioelectrodes exhibit higher stability under pH conditions of optimum enzymatic activity, as well as better sensitivity, and reproducibility for glucose detection via amperometric titration.

{AsW9O33}-{Mo3S4} based polyoxometalates including a metal-metal bond with Pd or Ni. Synthesis, structure and studies in solution.

Heterometallic cuboidal clusters [Mo(3)S(4)M(H(2)O)(9)Cl](3+) M = Pd or Ni react with the trivacant [AsW(9)O(33)](9-) anion to give tetramodular complexes [(H(2)AsW(9)O(33))(4){Mo(3)S(4)M(H(2)O)(5)}(2)](20-) (M = Pd for anion 2 and M = Ni for anion 3) in good yield. Both anions crystallized as single crystals of potassium salts to give K-2 and K-3 salts which have been characterized structurally by X-ray diffraction. Both compounds are isomorphous and the anions 2 and 3 are described as two dimeric moeties, associated by internal hydrogen bonds, electrostatic interactions involving four outer potassium ion and coordination bonds within a central {M(2)S(2)} unit containing a M-M metallic bond. Studies in solution reveal that the dimeric association is maintained in solution in the 2 × 10(-4)-2 × 10(-3) mol L(-1) range. Conversely, in the presence of exogeneous ligands, such as iodide or pyridine the UV-vis data are consistent with the dissociation of the anion 2 into monomer through a Pd-L coordination bond (L = I(-) or Py). Furthermore, (183)W NMR spectrum of 2 shows that molecular structure of 2 is retained in solution. Elemental analysis and IR are also supplied. Electrochemical behavior of 2 and 3 are given and compared with the Pd or Ni free parent anion. The CVs are dominated mainly by irreversible reduction or oxidation processes, where the peak potentials appear dependent upon the ionic charge of the complex. However, the CV of the Pd-containing anion (2) is consistent with the deposition of Pd metal at the electrode, which gives rise to an oxidation process into palladium oxide.

[Re(η2-CS3)4]3−, a new trithiocarbonate-containing rhenium(V) dodecahedral anion

The mononuclear complex (NMe4)3[Re(η2-CS3)4] has been prepared by adding CS2 to ReS−4 in a mixture of MeOH and NH3. During the reaction, ReVII is reduced to ReV, the measured diamagnetism (X = −3.04 × 10−4cm3mol−1) of the complex showing that the two added electrons are coupled. (NMe4)3[Re(η2-CS3)4] crystallizes in the space group Fddd, a = 11.985(4) Å, b = 23.001(11) Å, c = 47.463(19) Å, V = 13085(9) Å3. The reaction of CS2 results in the formation of trithiocarbonates bonded to the rhenium in a dodecahedral geometry.

Molecular architecture of copper (I) thiometallates: synthesis and characterization of [ReS4Cu3Cl5]3-, a geometry derived from the single cubane-like structure

The new rhenium-copper heteronuclear complex [NEt4]3[ReS4C3Cl5]2, was obtained as black crystals in 65% yield, from the reaction of [NEt4[[ReS4], [NEt4][CuCl2], and [NEt4][Cl] at - 20°C in acetone, while at room temperature without additional chloride [NEt4]2[ReS4Cu3Cl4]1 crystallized as black crystals in 60% yield. Crystal data for2: space group Pl,a=10.331(4) A,b=14.261(2) A,c= I4.458(3) A, α=78.55(1)°, β=81.83(3)°, γ=83.66(3)°,Z=2, 6480 reflections;R=0.058. For1: space group C2/c,a=20.969(5)A,b=12.955(5)A,c=22.827(8)A, β=91.16(2)°, Z=8, 3208 reflections,R = 0.052, The geometry of2 can be viewed as restllting from the opening of the cubane-like structure of1.

Acidification of [WS4]2–. Synthesis and structures of di-µ-sulfido-bis[(2,2′-bipyridine)chlorooxotungsten(V)] and di-µ-sulfido-bis[(2,2′-bipyridine)bromooxotungsten(V)]

Acidification of [WS4]2– by HCl or HBr in MeCN in the presence of 2,2′-bipyridine (bipy) led to the neutral dinuclear complexes [W2S2O2X2(bipy)2](X = Cl 1 or Br 2) which have been isolated as crystals. The structures of 1 and 2 were solved by X-ray diffraction methods, and were found to be isomorphous. Each tungsten(V) is bonded to a bipy ligand throuph the two nitrogen atoms, one in an axial, and the other in an equatorial position. The remaining axiai position of the octahedron is occupied by a terminal oxygen. The co-ordination is completed by a terminal halide and a bridging sulfur. A metal–metal bond is postulated between the two WV atoms, in accord with the diamagnetism of the crystals. The formation of compounds 1 and 2 has been analysed in comparison to the formation of [W4S12]2– under the same conditions of acidity but in the absence of 2,2′-bipyridine.