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The decomposition of the ruthenium precursor Ru(COD)(COT) (1, COD = 1,5-cyclooctadiene; COT = 1,3,5-cyclooctatriene) in mild conditions (room temperature, 1--3 bar H(2)) in THF leads, in the presence of a stabilizer (polymer or ligand), to nanoparticles of various sizes and shapes. In THF and in the presence of a polymer matrix (Ru/polymer = 5%), crystalline hcp particles of uniform mean size (1.1 nm) homogeneously dispersed in the polymer matrix and agglomerated hcp particles (1.7 nm) were respectively obtained in poly(vinylpyrrolidone) and cellulose acetate. The same reaction, carried out using various concentrations relative to ruthenium of alkylamines or alkylthiols as stabilizers (L = C(8)H(17)NH(2), C(12)H(25)NH(2), C(16)H(33)NH(2), C(8)H(17)SH, C(12)H(25)SH, or C(16)H(33)SH), leads to agglomerated particles (L = thiol) or particles dispersed in the solution (L = amine), both displaying a mean size near 2--3 nm and an hcp structure. In the case of amine ligands, the particles are generally elongated and display a tendency to form worm- or rodlike structures at high amine concentration. This phenomenon is attributed to a rapid amine ligand exchange at the surface of the particle as observed by (13)C NMR. In contrast, the particles stabilized by C(8)H(17)SH are not fluxional, but a catalytic transformation of thiols into disulfides has been observed which involves oxidative addition of thiols on the ruthenium surface. All colloids were characterized by microanalysis, infrared spectroscopy after CO adsorption, high-resolution electron microscopy, and wide-angle X-ray scattering.

Self-organization of nanoparticles into two- and three-dimensional superlattices on a large scale is required for their implementation into nano- or microelectronic devices. This is achieved, generally after a size-selection process, through spontaneous self-organization on a surface, layer-by-layer deposition or the three-layer technique of oversaturation, but these techniques consider superlattices of limited size. An alternative method developed in our group involves the direct formation in solution of crystalline superlattices, for example of tin nanospheres, iron nanocubes or cobalt nanorods, but these are also of limited size. Here, we report the first direct preparation in solution of multimillimetre-sized three-dimensional compact superlattices of nanoparticles. The 15-nm monodisperse FeCo particles adopt an unusual short-range atomic order that transforms into body-centred-cubic on annealing at 500 degrees C. The latter process produces an air-stable material with magnetic properties suitable for radiofrequency applications.

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The synthesis of shape controlled platinum nanoparticles has been investigated through an organometallic approach starting from the complex Pt2(dba)3 and using a long alkyl chain amine, hexadecylamine (HDA), as stabilizer. The influence of the experimental parameters (reactive gas and solvent nature, stabilizer/metal ratio, reactants concentration, temperature) on the shape of the Pt nanoparticles has been studied. Various shaped platinum nanostructures such as isolated nanoparticles, dendrites or crystalline nanowires were obtained, depending on the reaction conditions. This method takes profit of the mild conditions of chemistry in solution and allows obtaining regular nanostructures, most of them being homogeneous in shape as well as in size (isolated nanoparticles) or diameter/length (nanowires). Transmission electron microscopy and wide‐angle X‐ray scattering were used as characterization techniques. Beside the Knight‐shift effect of platinum, NMR solution investigations clearly evidenced the coordination of the amine at the Pt particles surface and its mobility. This mobility, increased when H2 is used as reactive gas for the precursor decomposition, favors the particles coalescence into nanowires. This phenomenon is also favored by the “soft” template character of the amine in particular in toluene solution.

The control of nanocrystal structures at will is still a challenge, despite the recent progress of colloidal synthetic procedures. It is common knowledge that even small modifications of the reaction parameters during synthesis can alter the characteristics of the resulting nano-objects. In this work we report an unexpected factor which determines the structure of cobalt nanoparticles. Nanocrystals of distinctly different sizes and shapes have resulted from stock solutions containing exactly the same concentrations of [Co{N(SiMe(3))(2)}(2)(thf)], hexadecylamine, and lauric acid. The reduction reaction itself has been performed under identical conditions. In an effort to explain these differences and to analyze the reaction components and any molecular intermediates, we have discovered that the rate at which the cobalt precursor is added to the ligand solution during the stock solution preparation at room temperature becomes determinant by triggering off a nonanticipated side reaction which consumes part of the lauric acid, the main stabilizing ligand, transforming it to a silyl ester. Thus, an innocent mixing, apparently not related to the main reaction which produces the nanoparticles, becomes the parameter which in fine defines nanocrystal characteristics. This side reaction affects in a similar way the morphology of iron nanoparticles prepared from an analogous iron precursor and the same long chain stabilizing ligands. Side reactions are potentially operational in a great number of systems yielding nanocrystals, despite the fact that they are very rarely mentioned in the literature.

Multielectron reductions such as the hydrogen evolution reaction (HER) play an important role in the development of nowadays energy economy. Herein, the application of the organometallic approach as synthetic method allows obtaining very small, ligand-capped but also highly active ruthenium nanoparticles (RuNPs) for the HER in both acidic and basic media. When deposited onto glassy carbon, the catalytic activity of this nanomaterial in 1 M H 2 SO 4 solution is highly dependent on the oxidation state of the NPs surface, with metallic Ru sites being clearly more active than RuO 2 ones. In sharp contrast, in 1 M NaOH as electrolyte, the original Ru/RuO 2 mixture is maintained even under reductive conditions. Estimation of surface active sites and electrochemically active surface area (ECSA) allowed benchmarking this catalytic system, confirming its leading performance among HER electrocatalysts reported at both acidic and basic pH. Thus, in 1 M NaOH condition, it displays lower overpotentials (η 0 ≈ 0 mV, η 10 = 25 mV) than those of commercial Pt/C and Ruthenium black (Rub), and also fairly outperforms them in short-and long-term stability tests. In 1 M H 2 SO 4 solution, it clearly outdoes commercial Rub and is competitive or even superior to commercial Pt/C, working at very low overpotentials (η 0 ≈ 0 mV, η 10 = 20 mV) with a Tafel slope of 29 mV•dec −1 , achieving TOFs as high as 17 s −1 at η = 100 mV and reaching a current density of |j| = 10 mA•cm −2 for at least 12 h without any sign of deactivation.

Stable iron nanoparticles have been synthesised by the decomposition of {Fe(N[Si(CH(3))(3)](2))(2)}(2) under dihydrogen pressure. Those conditions lead to a system of monodisperse and metallic nanoparticles which diameter is less than 2 nm and stabilized by HN[Si(CH(3))(3)](2). The magnetization is found to be M(S)=1.92 mu(B)/at., i.e., 10% lower than the bulk value. The Mossbauer spectrum is fitted by two contributions of metallic iron. The magnetic anisotropy energy constant increases up to 5.2x10(5) J/m(3), i.e., ten times the bulk one