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International audience; The sintering of uranium oxide powders prepared by hydrothermal conversion of oxalates was studied. A dilatometric study first showed that among the synthesis conditions, only the pH largely impacted the densification, notably through the powders morphology. Three samples (single crystals-pH = 1, microspheres-pH = 2 and nano-powders-pH = 8) were further selected to study their sintering behaviour. Densitometric and granulometric data then allowed establishing sintering maps. For single crystals and microspheres, densities above 96%TD were obtained at 1700°C. In contrast, only 2 to 8 hours at 1500°C were needed to yield comparable results for nano-powders. These observations confirm that the hydrothermal conversion of oxalates can be considered as a promising route for the synthesis of actinide oxides, which can subsequently be sintered directly.

Within the development of future nuclear reactors, wet chemistry routes have been investigated for the fabrication of advanced oxide fuels. In this frame, a multiparametric study focused on the hydrothermal conversion of uranium(IV) oxalate U(C2O4)2·nH2O into uranium oxides was undertaken in order to unravel the effects of temperature, pH, and kinetics. For pH ≤ 1, the lowest temperatures explored (typically from 180 to 200 °C) led to stabilized UO2+x/U4O9 mixtures exhibiting a global O/U ratio evaluated as 2.38 ± 0.10 from U M4-edge HERFD-XANES experiments. Higher temperatures (220-250 °C) led the oxide stoichiometry to decrease down to 2.13 ± 0.04 which corresponds to a lower fraction of U4O9 in the mixture. Additionally, increasing the temperature of the hydrothermal treatment efficiently improved the elimination of residual carbon species and water. Hydrothermal conversion of U(C2O4)2·nH2O also led to a drastic modification of the powders morphology. With this aim, pH tuning could be used to shift from bipyramidal aggregates (up to pH 1) to microspheres (2 ≤ pH ≤ 5) and then to nanometric powders (pH > 5). Finally, a kinetics study showed that uranium oxides can be obtained from the hydrothermal decomposition of oxalate within only few hours. If the samples collected early during the treatment always presented the characteristic XRD lines of UO2+x/U4O9 fluorite-type structure, then they were found to be strongly oxidized (O/U = 2.65 ± 0.14) which suggested the existence of a U(VI)-bearing amorphous secondary phase. The latter further tended to reduce through time. Hydrothermal conversion then probably proceeds as a two-step mechanism composed by the oxidative decomposition of uranium(IV) oxalate followed by the reduction of uranium by organic moieties and its hydrolysis. It appears as an easy and efficient way to yield highly pure uranium oxide samples in solution.

Hydrothermal conversion of thorium oxalate, Th(C

International audience; Obtaining bulk materials ordered at the nanoscale using nanoparticles as building blocks is a new challenge for scientists and is of primary interest in some research areas. In this study, we developed a simple one-pot route towards nanostructured hybrid materials based on uranium oxide through a non-hydrolytic condensation process under mild solvothermal conditions (T = 160 °C) using ditopic organic linkers as structuring agents. The obtained materials present a sand rose morphology composed of agglomerated nanometric sheets with a lamellar substructure. Nanometric sheets are composed of inorganic fringes consisting of a studtite phase [(UO2)O2(H2O)2]·2H2O that alternates with organic fringes formed by the structuring organic linker. A multiparametric study based on SAXS experiments and TEM analyses has highlighted the control of structural parameters by varying some synthesis conditions. The interlamellar distances are tunable from 1.60 nm to 1.94 nm through the length of the structuring linker and the inter-sheet distance from 1.85 nm to 2.10 nm through synthesis temperature. This efficient one-pot route appears to be very promising for the production of tunable multiscale nanostructured hybrid materials and can be implemented in many research areas, paving the way for various applications.

Hydrothermal conversion of thorium oxalate, Th(C2O4)2·nH2O, into thorium dioxide was explored through a multiparametric study, leading to some guidelines for the preparation of crystallized samples with the minimum amount of impurities. As the formation of the oxide appeared to be operated through the hydrolysis of Th4+ after decomposition of oxalate fractions, pH values typically above 1 must be considered to recover a solid phase. Also, because of the high stability of the thorium oxalate precursor, hydrothermal treatments of more than 5 h at a temperature above 220 °C were required. All the ThO2·nH2O samples prepared presented amounts of residual carbon and water in the range 0.2-0.3 wt % and n ≈ 0.5, respectively. A combined FTIR, PXRD, and EXAFS study showed that these impurities mainly consisted of carbonates trapped between elementary nanosized crystallites, rather than substituted directly in the lattice, which generated a tensile effect over the crystal lattice. The presence of carbonates at the surface of the elementary crystallites could also explain their tendency to self-assembly, leading to the formation of spherical aggregates. Hydrothermal conversion of oxalates could then find its place in different processes of the nuclear fuel cycle, where it will provide an interesting opportunity to set up dustless routes leading from ions in solution to dioxide powders in a limited number of steps.

The interest in metal–organic frameworks (MOFs) is growing exponentially due to their remarkable properties (high porosity, large surface area, thermal, and mechanical stability). They are usually synthesized as bulk crystalline solid materials. However, the sustainable development of MOFs as technological systems, material design and tuning their shape are of prime importance in order to use them as efficient devices. The development of deposition or the growing approaches of these materials on various supports provide useful techniques to reach this goal. Moreover, to study some particular properties, such as optical, catalysis, or even photocatalysis, MOFs need to be attached onto transparent conductive oxide (TCO) supports, such as indium tin oxide (ITO) or fluorine-doped tin oxide (FTO). This review is focused on the early advances in the growth and deposition of MOFs on TCO supports via various conventional methods.

International audience; A simple wet chemistry route towards micrometric spherical UO2 particles was designed through the conversion of uranium(IV) aspartate under mild hydrothermal conditions (T = 160 °C). A multiparametric study examining the effects of hydrothermal treatment duration, the initial uranium/aspartic acid molar ratio and magnetic stirring allowed us to point out the role of organic species in the shaping of the particles and to specify the operating conditions leading to monodisperse and size-controlled particles. In a turbulent flow regime (i.e. Rea > 104), particles with a diameter ranging from 400 nm to 2500 nm were obtained with a typical dispersion of less than ±10%. Moreover, the protocol was found to be robust and reproducible, with only limited size variation from one batch to another (typically less than ±5% on the particle diameter). The effect of an additional heat treatment step was also investigated which showed that residual traces of water and organics can be removed after firing at 600 °C without altering the initial morphology. This wet chemistry route appears to be very promising for the production of spherical UO2 particles and can be simply implemented in any nuclear chemistry lab, which paves the way to applications of such materials in various scientific areas.

International audience; The synthesis of original crystalline thorium aspartate tetrahydrate, Th(C4NO4H6)4.4H2O, was performed using two different wet-chemistry routes, involving either L-asparagine or L-aspartic acid as complexing agent. Characterization of this compound through 13C NMR and PXRD led to confirm the terminal coordination mode of the aspartate group and to suggest a potential cubic lattice (Pn-3 space group). Vibrational spectroscopy data were also collected. The conversion of thorium aspartate tetrahydrate into thorium dioxide was further performed through classical high temperature heat treatment or under hydrothermal conditions. On the one hand, thermal treatment provided a pseudomorphic conversion which retained the starting morphology, and favored the increase of the average crystallite size, as well as the complete elimination of the residual carbon content. On the other, hydrothermal conversion could be used to tune the morphology of the final oxide, ThO2.nH2O microspheres being prepared when starting from L-asparagine.

A series of Ru–Co dinuclear complexes have been synthesized and assayed as photocatalysts for the reduction of CO2 to CO in organic solvents. The Ru–Co complexes, with tris-diimine coordination at the Co ion, are the best supramolecular photocatalysts for CO2 reduction with a non-noble metal catalytic center reported so far.

Synthesis of new fluorinated tertiary malonamides (F-malonamides) was accomplished, and their liquid/liquid (L/L) extraction properties with f -elements were investigated. These molecules are fluorinated analogues of well known extractants used in several processes designed towards the treatment of nuclear wastes, and the efficient separation of lanthanides from minor actinides; however, the synthesis of F-malonamides deserved a modification of the general synthetic route commonly employed to prepare H-malonamides. Extraction of neodymium from various aqueous media into both fluorous and classical solvents was studied, which revealed an opposite trend between F-malonamides and H-malonamides: L/L extraction ability is very sensitive to the nitrogen atoms substitution pattern, and the most efficient F-malonamide is compound 3 (R 1 = Me), whereas the best H-malonamide is compound 5 (R 1 = Bu, DMDBTDMA).

This work highlights the relative importance between structural issues, longer range interactions and solvent effects for a series of ruthenium compounds on their electrochemical and photochemical properties. To study these effects, eight complexes of general formula [Ru(bpy)2(L)]2+ have been synthesized and characterized, where L represents substituted phenyl-imidazophenanthrolines (pip), dipyridophenazines (dppz) and pyrazinophenanthrolines (pzp). This experimental work supported by an important theoretical investigation has pointed out that the electrochemical and the photo-physical behavior of these types of molecular systems depends mainly of the close environment around the photosensitizer. A relation between the ditopic ligand structure (aromatic central part and/or the distal substituents) and the absorption properties have been observed, along with the lower reduction potential of dipyridophenazine and pyrazinophenanthroline moieties. This study points out the influence of the nature of the distal substituents, as well as the significant impact of the solvent nature and the interaction with water molecules, on the photo-physical properties of these ruthenium compounds.

A series of dinuclear [(bpy)2Ru(L)Ru(bpy)2]4+ and mononuclear ruthenium(II) complexes [(bpy)2Ru(L)]2+ where bpy is 2,2′-bipyridine and L represents 2,6-di(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)aryl ligands (DIP) were synthetized and characterized. An original pathway is proposed to obtain mono and hetero bi- and polymetallic Ru complexes and the relation between the molecular structure, the photophysical and electrochemical properties of the single Ru complexes is analysed. The investigated aryl cores are benzene, pyridine and 4-tert-butyl phenol. This work is focused on the effect of the aromatic moiety on the photoinduced charge transfer in the bimetallic compounds and the results are compared with the monometallic analogues. The absence of effect on the UV-visible absorption spectra and on the redox behavior upon varying the nature of the aryl moiety show that the two metallic centres in [(bpy)2Ru(L)Ru(bpy)2]4+ complexes are independent. However, luminescence measurements coupled with DFT calculations highlight a different photophysical behaviour between mono and dinuclear compounds incorporating the benzene core. Theoretical DFT and TD-DFT modelling was used to support the studied physico-chemical properties of these molecular systems.

A series of bimetallic coordination polymers were synthesised from lanthanide salts (chlorides or nitrates of Ce, Nd, Gd) and 2,5-dihydroxy-1,4-benzoquinone (DHBQ) under aqueous and anhydrous conditions, to be used as preceramics for mixed oxide synthesis. Syntheses in water or tetrahydrofuran (THF) gave rise to two different types of metal–organic frameworks. A new polymeric species, [Gd(DHBQ)Cl(THF)2]n, was characterised by single-crystal X-ray diffraction {[Gd(DHBQ)Cl(THF)2]n, a = 8.643(2) A, b = 9.917(5) A, c = 10.422(3) A, α = 104.611(3)°, β = 109.623(3)°, γ = 96.097(3)°, V = 796.1(5) A3, triclinic, P, Z = 2}. Characterisation by IR and Raman spectroscopy, powder X-ray diffraction and scanning electron microscopy showed that the mixed-metal polymers are solid solutions and highlighted the fact that their shape and morphology are strongly influenced by the presence of water in the reaction mixture. Micrometric, well-defined cylindrical objects were obtained from the aqueous synthesis, while the reaction in anhydrous THF led to nanometric spheres. Calcination at 850 °C of the coordination polymer preceramics easily yielded mixed NdxGd(1–x) and NdxCe(1–x) oxides as solid solutions, in which x varies between 0 and 1. The morphology of the preceramic powders is retained upon calcination. This allows easy control of some of the oxide properties from the coordination compound synthesis step. Indeed, BET measurements pointed out that the choice of anhydrous reaction conditions for the preceramic synthesis leads to enhancement of the specific surface areas of the oxides by one order of magnitude.

We present a new approach for homogeneous real-time immunodiagnostics (denoted as "PlasMag") that can be directly carried out in sample solutions such as serum, thus promising to circumvent the need of sample preparation. It relies on highly sensitive plasmon-optical detection of the relaxation dynamics of magnetic nanoparticles immersed in the sample solution, which changes when target molecules bind to the surfaces of the nanoparticles due to the increase in their hydrodynamic radii. This method requires hybrid nanoparticles that combine both magnetic and optical anisotropic properties. Our model calculations show that core-shell nanorods with a cobalt core diameter of 6 nm, a cobalt core length of 80 nm, and a gold shell thickness of 5 nm are ideally suited as nanoprobes. On the one hand, the spectral position of the longitudinal plasmon resonance of such nanoprobes lies in the near-infrared, where the optical absorption in serum is minimal. On the other hand, the expected change in their relaxation properties on analyte binding is maximal for rotating magnetic fields as excitation in the lower kHz regime. In order to achieve high alignment ratios of the nanoprobes, the strength of the magnetic field should be around 5 mT. While realistic distributions of the nanoprobe properties result in a decrease of their mean optical extinction, the actual relaxation signal change on analyte binding is largely unaffected. These model calculations are supported by measurements on plain cobalt nanorod dispersions, which are the base component of the aspired core-shell nanoprobes currently under development.

Treatment of Cp*2UI2 with KCN in thf led to the formation of Cp*2U(CN)2 (2), which further reacted with NR4CN to give [Cp*2U(CN)3][NR4] (R = Et, 3; R = nBu, 3‘) and [Cp*2U(CN)5][NR4]3 (R = Et, 4; R...

Addition of NnBu4CN to (C5Me5)2UI(py), (C5Me5)2CeI, or (C5Me5)2M(OTf) (M = U, Ce) in acetonitrile led to the precipitation of the neutral monocyanide species [(C5Me5)2M(μ-CN)]n [M = U (1), Ce (2)], which likely have an oligomeric structure, as shown by the trimeric cyanide-bridged complex [(C5Me5)2Ce(μ-CN)(CNtBu)]3 (3) obtained by addition of excess tBuNC into a suspension of 2 in acetonitrile. The structure of the U(III,IV) mixed valence compound [{(C5Me5)2U}2(μ-CN){(μ-CN)2Na(thf)}2]∞ (4), which crystallized from a thf solution of (C5Me5)2UI(py) in the presence of excess NaCN, reveals a unique example of an f-element−(μ-CN)−M interaction (M = main group or d transition metal). The anionic polycyanides [(C5Me5)2M(CN)3][NnBu4]2 [M = U (5), Ce (6)] were synthesized by treatment of 1 and 2 with 2 equiv or an excess of NnBu4CN in acetonitrile; they were also prepared in a one-pot procedure by stepwise addition of 1 equiv of KCN and 2 equiv of NnBu4CN to the parent iodides in acetonitrile. The bent metallocene...

Reactions of Cp*2UCl2 with a slight excess of Me3SiI or Me3SiOTf in acetonitrile provide convenient routes to Cp*2UI2 (1) or Cp*2U(OTf)2 (2) (Cp* = η-C5Me5; OTf = OSO2CF3), which were isolated with...

The first X-ray characterization of an azacrown ferrocenyl chalcone [(C5H5)Fe(C5H4COCH=CHC6H4-p-aza-15-crown-5)] (2) is reported. Its cation electrochemical detection capabilities have been evaluated and its behaviour towards protonation and calcium addition has been thoroughly examined. The uncommon ligand–Ca2+ interaction process involves three species of different stoichiometry in equilibrium in solution. Their association constants have been calculated. These species are formed by interaction of calcium with both the azacrown and CO functions of compound 2, as evidenced by NMR and IR spectroscopy. The theoretical MESP analysis also suggests that, contrary to its N-ethyl-substituted homologue [(C5H5)Fe(C5H4COCH=CHC6H4NEt2)] (1a), both coordination sites of 2 are involved in this interaction process. The study highlights that the CO group of 2 improves the selectivity of the cation electrochemical detection whencompared to the known compound [(C5H5)Fe(C5H4CH=CHC6H4-p-aza-15-crown-5)]. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Alkylation of malondiamides with alkyl iodides gives only low yields of the corresponding alkylated derivatives, especially for the fluoroalkyl derivatives.

The U(IV) linear pentacyano metallocene [U(C(5)Me(5))(2)(CN)(5)][NEt(4)](3) reacted with 2 molar equivalents of pyridine N-oxide in THF or acetonitrile to give the U(VI) complex [UO(2)(C(5)Me(5))(CN)(3)][NEt(4)](2), the first uranyl species containing the cyclopentadienyl ligand; the crystal structure revealed that the steric effects of the (C(5)Me(5)) ligand force the {UO(2)}2+ ion to deviate from linearity.

Treatment of [Cp*(2)U(NCMe)(5)]X(2) [Cp* = C(5)Me(5), X = BPh(4) (1) or I (1')] or Cp*(2)UI(2) in acetonitrile with the polydentate aromatic nitrogen bases phen, terpy and R(4)btbp led to the formation of the linear uranium metallocenes [Cp*(2)U(NCMe)(3)(phen)]X(2) [X = BPh(4) (2), I (2')], [Cp*(2)U(NCMe)(2)(terpy)][BPh(4)](2) (4), [Cp*(2)U(NCMe)(Me(4)btbp)][BPh(4)](2) (5) and [Cp*(2)U(NCMe)(CyMe(4)btbp)][X](2), [X = BPh(4) (6), I (6')], [phen = 1,10-phenanthroline, terpy = 2,2':6,2''-terpyridine, Me(4)btbp = 6,6'-bis-(3,3,6,6-tetramethyl-1,2,4-triazin-3-yl)-2,2'-bipyridine, CyMe(4)btbp = 6,6'-bis-(3,3,6,6-tetramethyl-cyclohexane-1,2,4-triazin-3-yl)-2,2'-bipyridine]. The bent metallocene [Cp*(2)U(phen)(2)][BPh(4)](2) (3) was isolated from the reaction of 1 and two molar equivalents of phen in THF. The X-ray crystal structures of 2.2MeCN, 3.2THF, and 6'.2MeCN were determined.

Best of both worlds: Reduction of an organometallic Co precursor on preformed CdSe nanorods yields two distinct semiconducting-magnetic heterostructures (see picture). The selective growth of Co on the tips of CdSe first gives nanosphere-nanorod dimers, which evolve into nanorod-nanorod structures. In the hybrid objects the magnetic properties of Co remain intact, while the luminescence properties of CdSe are affected but not completely quenched.

International audience; The optical study of ferrocenyl ligands 1–2 is presented, and reveals several interesting points. Contrary to their monosubstituted counterparts, these ligands exhibit fluorescence properties in acetonitrile. They can detect calcium, and also barium, by four different techniques: NMR, electrochemistry, UV–Vis absorption spectroscopy and fluorimetry in the same solvent. Each ligand detects both salts in the same manner by UV–Vis absorption and by fluorimetry. The response depends on the nature of the N terminal groups of the ligand. In each case, the ligand–calcium interaction is complex and involves 3–5 species in equilibrium in solution. Their association constants have been determined by fitting the UV–Vis data. Remarkably, for 2 and the calcium salts, nearly the same set of association constants can be used to fit not only the UV–Vis data obtained with calcium triflate (in a restricted range of concentration) or with calcium perchlorate, but also the NMR data obtained with calcium triflate. Interestingly, these results strengthen the fact that, in this family of compounds, the azacrown derivatives are less sensitive to high calcium triflate concentrations than their simple N-alkyl homologues. It is noteworthy that the complex non-monotonous fluorescence behaviour of compounds 1 and 2 upon Ca2+ or Ba2+ addition is quite original for ferrocenyl chalcones. These ligands constitute scarce examples of multi-signalling fluorescent ferrocenyl chemosensors for Ca2+ and Ba2+ cations in CH3CN.

We show here that the disubstituted ferrocenyl chalcones 1 and 2 are good electrochemical sensors for calcium and barium in CH 3 CN. However, these two triflate salts are detected in a different way by both ligands. To clarify this point, a thorough and informative NMR study of the ligand–salt interactions is presented. The unusual shapes of the titration curves obtained depend on both the ligand and cation used. For example, they illustrate that ligand 1 mainly interacts with the metal by its CO functions, while ligand 2 also interacts by its azacrown groups. These curves also reflect complex equilibriums in solution involving several ligand–salt adducts detected by mass spectrometry. To evaluate the strength of these interactions, the association constants of all the species formed have been determined by fitting the NMR data. It is noteworthy that changing the diethylamino groups in molecule 1 by the azacrown residue enhances the selectivity for the calcium salt, as pointed out by the value of the association constant of the 2 Ca 2+ species. The synthesis of the protonated counterparts 3 and 4 was useful to clarify the electrochemical behaviour of 1 and 2 . Although the two ligand–salt interactions present several common points, the whole results obtained allow us to propose an original explanation for the difference observed between the Ca 2+ and Ba 2+ electrochemical sensing.

The dication [(C5Me5)2U(NCMe)5]2+ was obtained by dissolving (C5Me5)2UI2 in acetonitrile or by treating (C5Me5)2UMe2 with HNEt3BPh4 in acetonitrile. The crystal structure revealed that the cyclopentadienyl rings are parallel and equidistant to the plane defined by the metal center and nitrogen atoms of the five MeCN ligands. Fifty years after the discovery of ferrocene, this compound represents a unique example of linear metallocene with auxiliary ligands in the equatorial girdle; it is also the first linear sandwich complex of an f-element.

We show how structural changes in the basic framework of ferrocenyl chalcone [(C 5 H 5 )Fe(C 5 H 4 COCH CHC 6 H 4 NEt 2 )] ( 1 ) induce different capabilities of detecting calcium by UV/vis absorption spectroscopy. In particular, compound 1 , and its derivatives ( 2 ) and ( 3 ) incorporating a supplementary ethylenic unit into the conjugated link, allow a specific detection of calcium triflate with regard to calcium perchlorate. Investigations related to the unprecedented behaviour of these chalcone-like derivatives are presented. This study confirms that while the interaction of ligands 1 – 3 with calcium is centred on the CO group, the interaction of ligand 4 with calcium is aza-centered. The strength of these interactions was examined by processing the UV/vis absorption data with a curve fitting model. Remarkably, in the case of compound 4 , the set of association constants issued from processing the absorption data was successfully used to fit the NMR data. In addition, mass spectrometry experiments provided strong support for the formation of the different species involved in the interaction of compounds 1 – 4 with calcium. This work underlines the importance of considering the nature of the salt used as well as the experimental conditions in cation detection processes.

International audience; A new ferrocene receptor binds a calcium guest via complex processes involving the whole unsaturated core of the ligand. Complexation induces significant changes in the ligand properties, as evidenced by the unprecedented cation sensing observed both by electrochemistry and fluorescence spectroscopy.

The title compound, [U(C10H15)2Cl2(C2H3N)], is a bent uranium(IV) metallocene, in contrast with the recently reported linear ones that can be obtained in acetonitrile with anions less strongly coordinating than chloride. The two chloride ions in the equatorial plane are located next to each other, with the acetonitrile ligand on one side.

We report on the synthesis and preparation of oriented nanomaterials of single crystalline metallic Co nanorods of 6 nm in diameters and two different aspect ratios (7 and 15). They display optimized magnetic properties, with a spontaneous magnetization just below the bulk one, and large coercive fields (up to 6.5 kOe at 300 K) as a result of coherent switching (i.e., Stoner and Wohlfarth mechanism). We measured a strong effective anisotropy very close to the expected value resulting from the sum of shape and magnetocrystalline contributions.