Frédéric Miserque

Self‐Assembly of a Heteropolyoxopalladate Nanocube: [PdII13AsV8O34(OH)6]8−

(Chemical Equation Presented) Not like the others: A molecular palladium oxide cluster was formed by self-assembly of palladium(II) and arsenic(V) using mild reaction conditions. The resulting heteropolypalladate [Pd II 13AsV 8O34(OH) 6]8- has a distorted cubic shape and edge lengths of about 1 nm. The thirteen PdII ions retain four-coordinate square-planar geometry, in marked contrast to all other known discrete polyoxometalates.

Hexa- and Dodecanuclear Polyoxomolybdate Cyclic Compounds: Application toward the Facile Synthesis of Nanoparticles and Film Electrodeposition

Two new compounds based on O(3)PCH(2)PO(3)(4-) ligands and {Mo(V)(2)O(4)} dimeric units have been synthesized and structurally characterized. The dodecanuclear Mo(V) polyoxomolybdate species in (NH(4))(18)[(Mo(V)(2)O(4))(6)(OH)(6)(O(3)PCH(2)PO(3))(6)] x 33 H(2)O (1) is a cyclohexane-like ring in a chair conformation with pseudo S(6) symmetry. In the solid state, the wheels align side by side, thus delimiting large rectangular voids. The hexanuclear anion in Na(8)[(Mo(V)(2)O(4))(3)(O(3)PCH(2)PO(3))(3)(CH(3)AsO(3))] x 19 H(2)O (2) has a triangular framework and encapsulates a methylarsenato ligand. (31)P NMR spectroscopic analysis revealed the stability of 2 in various aqueous media, whereas the stability of 1 depends on the nature of the cations present in solution. It has been evidenced that the transformation of 1 into 2 occurs in the presence of CH(3)AsO(3)(2-) ions. This behavior shows that 1 can be used as a new precursor for the synthesis of Mo(V)/diphosphonate systems. The two complexes were very efficient both as reductants of Pt and Pd metallic salts and as capping agents for the resulting Pt(0) and Pd(0) nanoparticles. The size of the obtained nanoparticles depends both on the nature of the polyoxometalate (POM; i.e., 1 or 2) and on the [metallic salt]/[POM] ratio. In all cases, X-ray photoelectron spectroscopy (XPS) measurements have revealed the presence of Mo(VI) species that stabilize the nanoparticles and the absence of Mo(V) moieties. Diffuse-reflectance FTIR spectra of the Pt nanoparticles show that the capping Mo(VI) POMs are identical for both systems and contain the diphosphonato ligand. The colloidal solutions do not show any precipitate and the nanoparticles remain well-dispersed for several months. The electrochemical reduction of Mo(V) species was studied for 2. Cyclic voltammetry alone and electrochemical quartz crystal microbalance coupled with cyclic voltammetry show the deposition of a film on the electrode surface during this reduction.

Synthesis of various crystalline gold nanostructures in water: The polyoxometalate β-[H4PMo12O40]3− as the reducing and stabilizing agent

This paper reports a facile, one-pot, room-temperature synthesis, in water, of various Au nanostructures using, as reducing agent, the mixed-valence polyoxometalate β-H3[H4P(MoV)4(MoVI)8O40]3−. By modifying the initial concentrations of the polyoxometalate and chloroauric acid, the morphology of the synthesized Au nanostructure can be tuned. The whole process is a “green-chemistry-type” synthesis of Au0 nanostructures.

Molecular-scale dynamics of light-induced spin cross-over in a two-dimensional layer

Spin cross-over molecules show the unique ability to switch between two spin states when submitted to external stimuli such as temperature, light or voltage. If controlled at the molecular scale, such switches would be of great interest for the development of genuine molecular devices in spintronics, sensing and for nanomechanics. Unfortunately, up to now, little is known on the behaviour of spin cross-over molecules organized in two dimensions and their ability to show cooperative transformation. Here we demonstrate that a combination of scanning tunnelling microscopy measurements and ab initio calculations allows discriminating unambiguously between both states by local vibrational spectroscopy. We also show that a single layer of spin cross-over molecules in contact with a metallic surface displays light-induced collective processes between two ordered mixed spin-state phases with two distinct timescale dynamics. These results open a way to molecular scale control of two-dimensional spin cross-over layers.

Interaction between uranium(VI) and siderite (FeCO3) surfaces in carbonate solutions

Abstract In order to assess the security of a long-term disposal of nuclear spent fuel, the prediction of radionuclide migration is needed. This paper presents the interaction between uranium(VI) and siderite surfaces, an iron carbonate present both in the near- and far-field of the storage, in carbonate solutions. The amount of uranium on the surface was determined after the interaction by alpha spectrometry. It appeared that the amount of uranium(VI) dropped with high pH and carbonate concentration, likely because of the predominance of UO2(CO3)22- and UO2(CO3)34- complexes in solution. The U4f X-ray photoelectron spectrum clearly highlighted that uranium present on the film has two different oxidation states and thus that uranium(VI) has been partially reduced by siderite.

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.

Grafting a Monolayer of Superparamagnetic Cyanide-Bridged Coordination Nanoparticles on Si(100)

The grafting of a monolayer of 6 nm superparamagnetic cyanide-bridged CsNiCr nanoparticles was achieved on a Ni(II)-functionalized Si(100) substrate; magnetic studies reveals that the grafted nanoparticles are nearly magnetically isolated within the monolayer.

Retention and redox behaviour of uranium(VI) by siderite (FeCO3)

Abstract In the context of long-term nuclear waste management, understanding the migration of a major component of spent fuel, uranium namely, in the environment is of major importance. This study presents the kinetics of uranium(VI) retention and reduction in carbonate solutions by siderite, an iron carbonate present both in the near- and far-field. At pH 9, uranium(VI) is retained at the surface, reduced and then precipitated into UO2.67. At pH 7, uranium(VI) seems, first, to be incorporated into iron precipitates at the solid/liquid interface and, subsequently, reduced by the Fe(II) contained in the thin layer.

Engineering the magnetic coupling and anisotropy at the molecule–magnetic surface interface in molecular spintronic devices

A challenge in molecular spintronics is to control the magnetic coupling between magnetic molecules and magnetic electrodes to build efficient devices. Here we show that the nature of the magnetic ion of anchored metal complexes highly impacts the exchange coupling of the molecules with magnetic substrates. Surface anchoring alters the magnetic anisotropy of the cobalt(II)-containing complex (Co(Pyipa)2), and results in blocking of its magnetization due to the presence of a magnetic hysteresis loop. In contrast, no hysteresis loop is observed in the isostructural nickel(II)-containing complex (Ni(Pyipa)2). Through XMCD experiments and theoretical calculations we find that Co(Pyipa)2 is strongly ferromagnetically coupled to the surface, while Ni(Pyipa)2 is either not coupled or weakly antiferromagnetically coupled to the substrate. These results highlight the importance of the synergistic effect that the electronic structure of a metal ion and the organic ligands has on the exchange interaction and anisotropy occurring at the molecule–electrode interface.

Tuning hydrogen production during oxide irradiation through surface grafting

Hydrogen production by radiolysis of water absorbed on solid is a major problem for nuclear waste management. In the present study, we demonstrate that controlling extreme surface properties of the irradiated material allows a direct tuning of the hydrogen production under irradiation. We achieve this control on a model system (silica fibers) using liquid phase atomic layer deposition (ALD) of titanium or zirconium oxide. The hydrogen production is strongly inhibited by the deposition of a subnanometric layer of titanium oxide, whereas it is amplified upon zirconium oxide grafting.