AuICl-bound N-heterocyclic carbene ligands form MII4(LAuCl)6 integrally gilded cages.

The incorporation of an N-heterocyclic carbene (NHC) moiety into a self-assembled MII4L6 cage framework required the NHC first to be metallated with gold(i). Bimetallic cages could then be constructed using zinc(ii) and cadmium(ii) templates, showing weak luminescence. The cages were destroyed by the addition of further gold(i) in the form of AuI(2,4,6-trimethoxybenzonitrile)2SbF6, which caused the reversibly-formed cages to disassemble and controllably release the AuI-NHC subcomponent into solution. This release in turn induced the growth of gold nanoparticles. The rate of dianiline release could be tuned by capsule design or through the addition of chemical stimuli, with different release profiles giving rise to different nanoparticle morphologies.

Shape-defined nanodimers by tailored heterometallic epitaxy.

The systematic construction of heterogeneous nanoparticles composed of two distinct metal domains (Au and Pt) and exhibiting a broad range of morphologically defined shapes is reported. It is demonstrated that careful Au overgrowth on Pt nanocrystal seeds with shapes mainly corresponding to cubeoctahedra, octahedra and octapods can lead to heterometallic systems whose intrinsic structures result from specific epitaxial relationships such as {111} + {111}, {200} + {200} and {220} + {220}. Comprehensive analysis shows also that nanoparticles grown from octahedral seeds can be seen as comprising of four Au tetrahedral subunits and one Pt octahedral unit in a cyclic arrangement that is similar to the corresponding one in decahedral gold nanoparticles. However, in the present case, the multi-component system is characterized by a broken five-fold rotational symmetry about the [011] axis. This set of bimetallic dimers could provide new platforms for fuel cell catalysts and plasmonic devices.

Characterisation of Co@Fe3O4 core@shell nanoparticles using advanced electron microscopy.

Cobalt nanoparticles were synthesised via the thermal decomposition of Co2(CO)8 and were coated in iron oxide using Fe(CO)5. While previous work focused on the subsequent thermal alloying of these nanoparticles, this study fully elucidates their composition and core@shell structure. State-of-the-art electron microscopy and statistical data processing enabled chemical mapping of individual particles through the acquisition of energy-filtered transmission electron microscopy (EFTEM) images and detailed electron energy loss spectroscopy (EELS) analysis. Multivariate statistical analysis (MSA) has been used to greatly improve the quality of elemental mapping data from core@shell nanoparticles. Results from a combination of spatially resolved microanalysis reveal the shell as Fe3O4 and show that the core is composed of oxidatively stable metallic Co. For the first time, a region of lower atom density between the particle core and shell has been observed and identified as a trapped carbon residue attributable to the organic capping agents present in the initial Co nanoparticle synthesis.

Dynamic nuclear polarization enhanced natural abundance 17O spectroscopy.

We show that natural abundance oxygen-17 NMR of solids could be obtained in minutes at a moderate magnetic field strength by using dynamic nuclear polarization (DNP). Electron spin polarization could be transferred either directly to (17)O spins or indirectly via (1)H spins in inorganic oxides and hydroxides using an oxygen-free solution containing a biradical polarization agent (bTbK). The results open up a powerful method for rapidly acquiring high signal-to-noise ratio solid-state NMR spectra of (17)O nuclear spins and to probe sites on or near the surface, without the need for isotope labeling.

Can polymorphism be used to form branched metal nanostructures?

Branched metal nanostructures are of great technological importance because of their unique size- and shape-dependent properties. A kinetically controlled synthesis that uses polymorphism to produce branched nickel nanoparticles is presented. These nanoparticles consist of a face-centred cubic (fcc) core and extended arms of alternating fcc and hexagonal close-packed (hcp) nickel phases.

New routes to Cu(I)/Cu nanocatalysts for the multicomponent click synthesis of 1,2,3-triazoles.

An array of copper and copper-zinc based nanoparticles (NPs) have been fabricated employing a variety of polymeric capping agents. Analysis by TEM, XRPD and XPS suggests that by manipulating reagent, reductant and solvent conditions it is possible to achieve materials that are mono-/narrow disperse with mean particle sizes in the ≤10 nm regime. Oxidative stability in air is achieved for monometallic NPs using poly(methyl methacrylate) (PMMA) anti-agglomerant in conjunction with a variety of reducing conditions. In contrast, those encapsulated by either poly(1-vinylpyrrolidin-2-one) (PVP) or poly(4-vinylpyridine) (PVPy) rapidly show Cu(2)O formation, with all data suggesting progressive oxidation from Cu to Cu@Cu(2)O core-shell structure and finally Cu(2)O. Bimetallic copper-zinc systems, reveal metal segregation and the formation of Cu(2)O and ZnO. Catalysts have been screened in the synthesis of 1,2,3-triazoles through multicomponent azide-alkyne 1,3-dipolar cycloaddition. Whereas PMMA- and PVPy-coating results in reduced catalytic activity, those protected by PVP are highly active, with quantitative triazole syntheses achieved at room temperature and with catalyst loadings of 0.03 mol% metal for Cu and CuZn systems prepared using NaH(2)PO(2), N(2)H(4) or NaBH(4) reductants.

Synthesis, alignment, and magnetic properties of monodisperse nickel nanocubes.

This Communication describes the synthesis of highly monodispersed 12 nm nickel nanocubes. The cubic shape was achieved by using trioctylphosphine and hexadecylamine surfactants under a reducing hydrogen atmosphere to favor thermodynamic growth and the stabilization of {100} facets. Varying the metal precursor to trioctylphosphine ratio was found to alter the nanoparticle size and shape from 5 nm spherical nanoparticles to 12 nm nanocubes. High-resolution transmission electron microscopy showed that the nanocubes are protected from further oxidation by a 1 nm NiO shell. Synchrotron-based X-ray diffraction techniques showed the nickel nanocubes order into [100] aligned arrays. Magnetic studies showed the nickel nanocubes have over 4 times enhancement in magnetic saturation compared to spherical superparamagnetic nickel nanoparticles.

Nanoparticulate PdZn--pathways towards the synthetic control of nanosurface properties.

This paper reports an in-depth structural investigation of PdZn nanoparticulates prepared over an entire compositional range. By using a combination of HRTEM, ICP-OES, EDX and XPS alongside PXRD, we are able to show how a liquid-type reduction process can be exploited to target different PdZn bimetallic structures while maintaining reproducibly narrow particle size distributions and average particle diameters of approximately 3 nm. Samples have been further analyzed by quantitative phase analysis of the Rietveld refined diffraction data, providing indications as to how variations in specific surface compositions are obtained when Zn is used as the alloying metal. The influence of nanolattice strain is investigated by geometric analysis of TEM data. Results suggest, in conjunction with previously published catalytic data, how different compositions of this specific bimetallic system may be exploited in catalytic processes to control substrate/product affinity. We thus demonstrate a new and simplified approach to PdZn bimetallics, which may offer novel perspectives for applications in industrial catalysis.

Nanoparticulate copper--routes towards oxidative stability.

A modified polyol-based reduction method in ethylene glycol that incorporates poly(N-vinylpyrrolidone) (PVP, M(av) = 10,000; 40,000; 55,000) as polymeric anti-agglomerant alongside a reducing additive (N(2)H(4) x H(2)O, NaBH(4), NaH(2)PO(2) x H(2)O) has been employed to investigate the influence of synthetic parameters on the purity, morphology and stability of an array of polymer-coated copper nanoparticles. While data point to ethylene glycol being capable of acting as a reductant in this system, the use of NaH(2)PO(2) x H(2)O as co-reductant in tandem with the presence of PVP (M(av) 40,000) has rendered nanoparticles with a mean size distribution of 9.6 +/- 1.0 nm that exhibit stability towards oxidation for several months. These data allow us to probe fundamentally how oxidatively stable nano-copper might be achieved.

Evidence for heterogeneous Sonogashira coupling of phenylacetylene and iodobenzene catalyzed by well defined rhodium nanoparticles.

Sonogashira coupling of phenylacetylene with iodobenzene has been studied in the presence of metallic Rh nanoparticle catalysts and found to occur via a surface-mediated heterogeneous route. Homogeneous catalytic processes due to Rh species that may leach into solution were barely detectable within the sensitivity of our experiments. Moreover, larger (8 nm) nanoparticles were found to be much better catalysts than very small ones (2 nm), which is consistent with the hypothesis that steric limitations adversely affect the efficiency of the latter.

Exploring the structural complexities of metal-metalloid nanoparticles: the case of Ni.B as catalyst.

Understanding of the structural complexities of metal-metalloid nanoparticles is at the heart of several proposals for investigating the physical properties and practical applications of these bi-elemental nanomaterials. To date, the most widely studied metal-metalloid is the nickel-boron (Ni.B) system; however, the exact nature of the structure of the material itself has remained unclear. Herein we show our systematic investigations of the material in an attempt to reveal its fascinating nanostructure. The relation between its high catalytic activity and the ultrafine structure is explored, and the work has been further extended to the formation of colloidal Ni.B nanoparticles. The results presented in this work may represent a substantial progress toward a full understanding of the nickel-boron chemistry.

The unusual nanostructure of nickel-boron catalyst.

A highly unusual nanostructure of the nickel-boron particulate material, initially synthesised in the 1950s and well known to be an exceedingly active hydrogenation catalyst, has been identified for the first time.

Direct conversion of iron stearate into magnetic Fe and Fe3C nanocrystals encapsulated in polyhedral graphite cages.

We report a direct salt-conversion approach for large-scale synthesis of carbon-encapsulated magnetic Fe and Fe3C nanoparticles.