Nickel nanoparticles of tunable shape have been synthesized in THF, in the presence of hexadecylamine (HDA) or trioctylphosphineoxide (TOPO), in mild conditions and characterized by HREM and SQUID measurements. The formation of nanorods is promoted by a high amine content in the reaction medium. In contrast to what is observed for TOPO-protected nickel particles, the saturation magnetization of HDA-capped nanoparticles is comparable to that of bulk nickel, which demonstrates that the coordination of an amine ligand does not alter the magnetic properties of nickel.

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.

The shape of things to come: Nanospheres, thermodynamically stable nanorods, and nanowires are selectively produced in solution from [Co(η3‐C8H13)(η4‐C8H12)] in the presence of oleic acid and various amines. The aspect ratio of the nanorods is controlled by the length of the alkyl chain of the amine. Nanorods with approximate dimensions of 9×40 nm (see Figure) are ferromagnetic at room temperature.

Nanokugeln, ‐röhrchen und ‐drähte nach Maß lassen sich selektiv aus einer Lösung von [Co(η3‐C8H13)(η4‐C8H12)] in Gegenwart von Ölsäure und verschiedenen Aminen herstellen. Dabei bestimmt die Alkylkettenlänge des Amins die Länge des Nanoröhrchens. Die Aufnahme zeigt Röhrchen von etwa 9×40 nm2, die thermodynamisch stabil und bei Raumtemperatur ferromagnetisch sind.

The reaction of Pt(dba) 2 with CO (1 atm) in toluene affords a brown precipitate which can be isolated and redissolved in CH 2 Cl 2 to give a colloidal solution of fcc platinum particles with a large size dispersity (10-20 Å, I). Redissolution of I in THF leads to stable 12 Å fcc platinum particles (II) which can be isolated and characterized by high-resolution electron microscopy (HREM) and wide-angle X-ray scattering (WAXS). The original reaction in THF leads to the direct formation of II. Addition of 0.2 equiv of PPh 3 to II yields a new colloid, III, of the same size but of icosahedral structure. III was characterized by HREM and spectroscopic techniques. In particular, 13 C and 31 P NMR spectroscopy demonstrates the absence of a Knight shift for these particles. Addition of excess triphenylphosphine leads to another species, IV, displaying broader size distribution with a maximum at 17 Å and an fcc structure. The reaction of I with more than 0.2 equiv of PPh 3 affords mixtures containing colloids, clusters (predominantly Pt 5 (CO) 6 (PPh 3 ) 4 ), and mononuclear complexes. Both the formation of the colloids and their transformation into molecular species is rapid at room temperature. It is suggested that such processes may be more frequent in organometallic chemistry than previously thought.

We describe the conversion of yttrium, barium, and copper trifluoracetate-derived solid precursors to epitaxial YBa 2 Cu 3 O x superconducting ceramics on (001)-oriented LaAlO 3 substrates. Transmission electron microscopy, electron energy loss spectroscopy, energy-dispersive X-ray analysis, and X-ray diffraction are used to characterize the reaction path and nucleation mechanism yielding high critical current YBa 2 -Cu 3 O 7 . Our results show that the pyrolysis of the trifluoracetate solutions yields a nanostructured, partially amorphous Ba 1-x Y x F 2+x matrix having a Ba/Y ratio close to 2, with homogeneously dispersed CuO nanoparticles. Upon heating, the chemical trajectory of the fluoride matrix and the overall microstructural evolution of the ceramic precursor prior to YBa 2 Cu 3 O 7 nucleation is driven by the decomposition and oxidation of this solid solution. The Y solid solubility decreases with temperature yielding Y 2 O 3 which reacts with the CuO particles forming Y 2 Cu 2 O 5 at about 700°C. In addition, electron energy loss spectroscopy reveals a high oxygen concentration and almost no Y in the matrix quenched from 795°C, at a stage where the YBa 2 Cu 3

The reaction of Pt(dba)2 with Ru(COD)(COT) in various proportions under dihydrogen in the presence of PVP leads to the formation of bimetallic nanoparticles of definite compositions resulting from the relative concentration of the two complexes in the initial solution. The progressive incorporation of ruthenium into the platinum matrix leads to structural changes from face-centered cubic (fcc) for high platinum contents to hexagonal close-packed (hcp) for high ruthenium contents. For the composition Pt1Ru3 a contraction of the size of the particles (ca. 1.1 nm) and of the size distribution indicates the presence of a new phase consisting of monodisperse particles for which a model of truncated twinned octahedrons of 79 atoms was proposed.

The reaction of Co(η3-C8H13)(η4-C8H12) and Pt2(dba)3 (dba = bis-dibenzylidene acetone) under dihydrogen leads in the presence of poly(vinylpyrrolidone) to nanometric bimetallic particles Co x Pt1 - x . The composition of the material is determined by the initial ratio of the two organometallic precursors. The bimetallic character of the particles is evidenced by magnetic, structural, and spectroscopic studies. Structural changes are evidenced both by HREM and WAXS:  platinum rich particles adopt a fcc crystalline structure while cobalt rich particles adopt a non periodic polytetraedral arrangement. The magnetic properties of the materials have been investigated. ZFC/FC measurements show that the particles are superparamagnetic and that their size dispersity is very low. From isothermal magnetization measurements, the extrapolated value of the coercive field H C (T = 0) is shown to increase continuously with Pt concentration, which is characteristic of bimetallic particles.