Submicrometer intermediates in the citrate synthesis of gold nanoparticles: new insights into the nucleation and crystal growth mechanisms

The reduction of tetrachloroaurate by citrate ions in aqueous solutions yielding gold nanoparticles (GNPs) has been studied using in situ tapping mode atomic force microscopy (AFM), UV-vis absorption and dynamic light scattering (DLS) spectroscopies, small-angle X-ray scattering (SAXS) along with ex situ TEM, EDX and XPS. Special attention is given to mesoscale intermediates responsible for the intense coloring of the transient solutions and their role in nucleation and crystal growth. AFM detects liquid droplet-like domains, globules 30-50 nm in diameter arranged in submicrometer aggregates in the gray and blue solutions, and well separated individual particles in the final red sols. DLS shows abrupt appearance of species about 30 nm and larger but not growing Au nanoparticles, while SAXS reveals gradually increasing nanoparticles and no aggregates. The mesoscale structures observed in TEM become looser as the reaction proceeds; they contain signatures of oxidized Au and other solutes. The results are interpreted in terms of decomposition of supersaturated solutions to afford domains ("dense droplets") enriched by gold, and then, after nucleation and coalescence of Au nuclei inside them, rather slow growth of gold nanoparticles within the associated globules; the color changes of the transient solutions are due to increasing interparticle distances.     

Magnetodielectric composites based on functionalized polyphenylene sulfides containing iron nanoparticles

Preparation of iron-filled polyaminophenylene sulfides and polyhydroxyaminophenylene sulfides by the metal vapor procedure was studied. Nanocomposites based on these metal-containing polymers and epoxy-isopropylidenediphenol oligomers (ED-20) were prepared and their composition, properties, and structure were studied by X-ray diffraction and thermogravimetric analyses, and thermomechanical methods. The magnetic and dielectric properties of the materials were determined.     

K3(U3O6)(Si2O7) and Rb3(U3O6)(Ge2O7): a pentavalent-uranium silicate and germanate

A new uranium(V) silicate, K3(U3O6)(Si2O7), and the germanate analogue, Rb3(U3O6)(Ge2O7), have been synthesized under high-temperature, high-pressure hydrothermal conditions and characterized by single-crystal X-ray diffraction. Their structures contain uranate columns formed of triple octahedral chains of the alpha-UF5 type linked by disilicate (or digermanate) units to form a 3-D framework structure. The valence state of uranium is confirmed by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and magnetic susceptibility.     

Structure of Nd<Subscript>5</Subscript>Mo<Subscript>3</Subscript>O<Subscript>16 + δ</Subscript> Single Crystals Doped with Tungsten

The structure of tungsten-doped Nd₅Mo₃O_{16 + δ} single crystals has been investigated by X-ray diffraction analysis, energy-dispersive X-ray spectroscopy (EDXS) microanalysis, and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Tungsten atom, which partially replaces molybdenum atoms in the structure, is found to be located close (at a distance of 0.57 Å) to the Mo atom site. The interstitial oxygen atom О3 shifts from the crystallographic site with coordinates (0.5, 0.5, 0) to the site with coordinates (0.43, 0.48, 0.04) and complements the tungsten coordination to octahedral. The decrease in the unit-cell parameter and conductivity with an increase in the tungsten concentration in the sample is shown to be related to the fact that the interstitial oxygen atom О3 (responsible for conductivity) is in the coordination environment of tungsten atom.     

Influence of Hydrogen Bonding in the Structure of Mixed-Ligand Copper(II) Chelates. Spectra and Structure of [Aquo((2,2′-Dipyridylamine)-(3-Chloro-2,4-Pentanedionato)Copper(II)] Nitrate

The IR, the ligand field spectra and the crystal structure of the mixed-ligand compound [(aquo)2,2-dipyridylamine(3-chloro-2,4-pentanedionato)copper(II)] nitrate, [Cu(dpyamH) Cl-acac(H₂O)]NO₃], are reported. The copper atom exists in a square pyramidal environment with the apical position occupied by the aqua ligand. The nitrogenous base and the -dionato anion act as bidentate ligands forming six-membered chelate rings. In addition to the coulombic interactions with the metal centre, the planar NO ₃ ^- group participates in specific electrostatic interactions involving the hydrogen atoms of the coordinated water molecule. The chlorine and the nitrogen atoms are also involved in hydrogen bonding. The structure of the compound was determined by single crystal X-ray diffraction analysis (triclinic, space group , a = 8.718(5), b = 9.407(5), c = 13.484 (7) Å, = 94.17(4)°, = 105.12(5)°, = 119.75(5)°, Z = 2, R = 0.0332, R _W = 0.0869).     

Electronic and atomic structure of platinum-cobalt nanocatalysts

X-ray diffraction in combination with X-ray emission and EXAFS spectroscopy were used to study the electronic and atomic structure of metal nanoparticles stabilized on a carbon support in novel Pt _x Co/C catalysts of different composition with the molar ratio Pt:Co (x) of 1 to 3. Cobalt atoms in nanoparticles, which average size was 2–4 nm, were shown to form chemical bonds both with platinum atoms and carbon atoms of the support material.     

Magnetic circular dichroism and the nature of ferromagnetism in colloidal gold nanoparticles

The spectra of optical absorption and of magnetic circular dichroism (MCD) have been measured in the 350–1150 nm wavelength range for a set of colloidal solutions containing Au nanoparticles with the average size of 6 nm having thiolate coatings with different degrees of chirality. The form of absorption and MCD spectra suggests the dipole character of interband transitions involving the 5d-6(sp) orbitals. The absence (within the experimental error) of the dependence of the MCD spectra on the coating type rules out the hypothesis on the orbital nature of the observed magnetism. We argue that the spin polarization plays the dominant role in the magnetism of gold nanoparticles with a thiolate coating.     

Structural features of green cobalt(III) hydroxide

Emission Mössbauer and X-ray absorption XANES/EXAFS spectroscopic techniques are applied to elucidate the structural features of green cobalt(III) hydroxide. A comparative analysis of structurally characterized cobalt(II) and cobalt(III) oxo-compounds shows that the parameters of the local environment of cobalt atoms in green cobalt(III) hydroxide differ substantially from those of its analogues.     

The First Heterometallic Acetate-Bridged Pt(II)–Pd(II) Complex: Synthesis,Structure, and Formation of Bimetallic PtPd2 Nanoparticles

Russian Journal of Coordination Chemistry - The reaction of platinum acetate blue, empirically described as Pt(OOCMe)2.50, with palladium(II) acetate Pd3(μ-OOCMe)6 gave the first...     

Comparative X-Ray Absorption Analysis of the Spectrum of Vacant Electronic States in Cobalt and Nickel Tetraphenylporphyrin Complexes

Physics of the Solid State - The energy distributions and the properties of the lower vacant electronic states in cobalt and nickel tetraphenylporphyrin complexes CoTPP and NiTPP are studied by...