Nanoparticle Ripening : A Versatile Approach for the Size and Shape Control of Metallic Iron Nanoparticles.

A novel approach for the synthesis of Fe(0) nanoparticles (NPs) with tunable sizes and shapes is reported. Ultrasmall Fe(0) NPs were reacted under mild conditions in the presence of a mixture of palmitic acid and amine ligands. These NPs acted not only as preformed seeds but also as an internal iron(II) source that was produced by the partial dissolution of the NPs by the acid. This fairly simple approach allows the strict separation of the nucleation and the growth steps. By changing the acid concentration, a fine tuning of the relative ratio between the remaining Fe(0) seeds and the iron(II) reservoir was achieved, giving access to both size (from 7 to 20 nm) and shape (spheres, cubes or stars) control. The partial dissolution of the ultrasmall Fe(0) NPs into iron(II) source and the successive growth was further studied by using combined TEM and Mössbauer spectroscopy. The successive corrosion, coalescence, and ripening observed could be understood in the framework of an environment-dependent growth model.

Designed single-source precursors for iron germanide nanoparticles: colloidal synthesis and magnetic properties.

The synthesis of iron germanide nanoparticles at the nanoscale is a challenging task. Here, we describe the preparation of nanocrystals of the hexagonal Fe1.67Ge phase via the thermolysis of single source precursors [{iPrNC(tBu)NiPr}RGe]Fe(CO)4 (where R = Cl, N(SiMe3)2) under mild conditions (200 °C). These bimetallic precursors and the corresponding germylenes [{iPrNC(tBu)NiPr}RGe] were fully characterized by spectroscopic techniques as well as single crystal X-ray diffraction. While the structural features of the molecular species were shown to be almost identical, the results of the thermolysis were highly dependent on the nature of R. When R = Cl, multimodal size distributions and non-controlled phases were obtained. In contrast, the thermolysis of [{iPrNC(tBu)NiPr}{N(SiMe3)2}Ge]Fe(CO)4 yielded pure ferromagnetic Fe1.67Ge nanoparticles with a mean diameter close to 6 nm and a narrow size distribution (<12%). These results were rationalized in terms of Ge-substituent bond energy thanks to a computational study.

Isoprene Polymerization on Iron Nanoparticles Confined in Carbon Nanotubes.

The confinement of air-protected metallic magnetic nanoparticles in the inner cavity of carbon nanotubes (CNTs) should offer an interesting perspective for biomedical applications or for controlling CNT alignment in composites. Because the direct confinement of polymer-precoated nanoparticles in CNTs could be restricted by diffusion limitations, we developed a process based on: 1) the confinement of iron nanoparticles surface-modified with an iron polymerization catalyst in the cavity of CNTs and 2) the polymerization of isoprene on the confined nanoparticles. The resulting material consists in CNT-confined iron nanoparticles coated with a polyisoprene air barrier. This approach constitutes a proof of concept for the development of smart materials for use in medicine or composites.

Complex Nano-objects Displaying Both Magnetic and Catalytic Properties: A Proof of Concept for Magnetically Induced Heterogeneous Catalysis.

Addition of Co2(Co)9 and Ru3(CO)12 on preformed monodisperse iron(0) nanoparticles (Fe(0) NPs) at 150 °C under H2 leads to monodisperse core-shell Fe@FeCo NPs and to a thin discontinuous Ru(0) layer supported on the initial Fe(0) NPs. The new complex NPs were studied by state-of-the-art transmission electron microscopy techniques as well as X-ray diffraction, Mössbauer spectroscopy, and magnetic measurements. These particles display large heating powers (SAR) when placed in an alternating magnetic field. The combination of magnetic and surface catalytic properties of these novel objects were used to demonstrate a new concept: the possibility of performing Fischer-Tropsch syntheses by heating the catalytic nanoparticles with an external alternating magnetic field.

Surfaces of a colloidal iron nanoparticle in its chemical environment: a DFT description.

Describing and understanding surface chemistry on the atomic scale is of primary importance in predicting and rationalize nanoparticle morphology as well as their physical and chemical properties. Here we present the results of comprehensive density functional theory studies on the adsorption of several small organic species, representing the major species (H2, Cl2, HCl, NH3, NH4Cl, and CH3COOH), present in the reaction medium during colloidal iron nanoparticle synthesis on various low-index iron surface models, namely, (100), (110), (111), (211), and (310). All of the tested ligands strongly interact with the proposed surfaces. Surface energies are calculated and ligand effects on the morphologies are presented, including temperature effects, based on a thermodynamic approach combined with the Wulff construction scheme. The importance of taking into account vibrational contributions during the calculation of surface energies after adsorption is clearly demonstrated. More importantly, we find that thermodynamic ligand effects can be ruled out as the unique driving force in the formation of recently experimentally observed iron cubic nanoparticles.

New generation of magnetic and luminescent nanoparticles for in vivo real-time imaging.

A new generation of optimized contrast agents is emerging, based on metallic nanoparticles (NPs) and semiconductor nanocrystals for, respectively, magnetic resonance imaging (MRI) and near-infrared (NIR) fluorescent imaging techniques. Compared with established contrast agents, such as iron oxide NPs or organic dyes, these NPs benefit from several advantages: their magnetic and optical properties can be tuned through size, shape and composition engineering, their efficiency can exceed by several orders of magnitude that of contrast agents clinically used, their surface can be modified to incorporate specific targeting agents and antifolding polymers to increase blood circulation time and tumour recognition, and they can possibly be integrated in complex architecture to yield multi-modal imaging agents. In this review, we will report the materials of choice based on the understanding of the basic physics of NIR and MRI techniques and their corresponding syntheses as NPs. Surface engineering, water transfer and specific targeting will be highlighted prior to their first use for in vivo real-time imaging. Highly efficient NPs that are safer and target specific are likely to enter clinical application in a near future.

A simple chemical route toward monodisperse iron carbide nanoparticles displaying tunable magnetic and unprecedented hyperthermia properties.

We report a tunable organometallic synthesis of monodisperse iron carbide and core/shell iron/iron carbide nanoparticles displaying a high magnetization and good air-stability. This process based on the decomposition of Fe(CO)(5) on Fe(0) seeds allows the control of the amount of carbon diffused and therefore the tuning of nanoparticles magnetic anisotropy. This results in unprecedented hyperthermia properties at moderate magnetic fields, in the range of medical treatments.

Stabilizing vortices in interacting nano-objects: a chemical approach.

We report a chemical method to prepare metallic Fe porous nanocubes. The presence of pores embedded inside the cubes was attested by electron tomography. Thanks to electronic holography and micromagnetic simulations, we show that the presence of these defects stabilizes the vortices in assembly of interacting cubes. These results open new perspectives toward magnetic vortex stabilization at relatively low cost for various applications (microelectronics, magnetic recording, or biological applications).

Room-temperature tunnel magnetoresistance in self-assembled chemically synthesized metallic iron nanoparticles.

We report on room temperature magnetoresistance in networks of chemically synthesized metallic Fe nanoparticles surrounded by two types of organic barriers. Electrical properties, featuring Coulomb blockade, and magnetotransport measurements show that this magnetoresistance arises from spin-dependent tunnelling, so the organic ligands stabilizing the nanoparticles are efficient spin-conservative tunnel barrier. These results demonstrate the feasibility of an all-chemistry approach for room temperature spintronics.

Silyl and sigma-silane ruthenium complexes: chloride substituent effects on the catalysed silylation of ethylene.

Silylation of ethylene by the chlorosilanes HSiMe(2)Cl and HSiMeCl(2) was catalysed by the bis(dihydrogen) complex RuH(2)(eta(2)-H(2))(2)(PCy(3))(2) (1). Dehydrogenative silylation leading to the formation of the corresponding vinylsilanes was in competition with hydrosilylation. The rate and selectivity of the reactions were influenced by the number of chloro substituents and the ethylene pressure. A comparative mechanistic study was performed in toluene-d(8) with the two chlorosilanes. Reaction of 1 with an excess of HSiMe(2)Cl (10 equiv.) produced the sigma-silane complexes RuH(2)(eta(2)-H(2))(eta(2)-HSiMe(2)Cl)(PCy(3))(2) (2Me(2)Cl), RuH(2)(eta(2)-HSiMe(2)Cl)(2)(PCy(3))(2) (3Me(2)Cl) and the silyl complex RuCl(SiMe(2)Cl)(eta(2)-H(2))(PCy(3))(2) (4Me(2)Cl), all characterised by multinuclear NMR spectroscopy. Complexes 2Me(2)Cl and 3Me(2)Cl adopt a cis configuration for the two bulky phosphine ligands as a result of stabilising SISHA (Secondary Interactions between Silicon and Hydrogen Atoms) interactions. Complex 4Me(2)Cl resulted from the stoichiometric reaction of HSiMe(2)Cl with 1 producing RuHCl(eta(2)-H(2))(PCy(3))(2)in situ which further reacted with evolution of H(2) and formation of 4Me(2)Cl. When reacting 1 with 10 equiv. of HSiMeCl(2), the corresponding complexes 3MeCl(2) and 4MeCl(2) were detected as well as traces of 2MeCl(2). The reactivity toward ethylene was then examined. Under catalytic conditions (excess silane in toluene-d(8), ethylene atmosphere) only two compounds could be characterised: free PCy(3) and the new (eta(6)-aryl)(disilyl) complexes of the general formula Ru(eta(6)-C(6)D(5)CD(3))(SiMe(3-n)Cl(n))(2)(PCy(3)) (6Me(3-n)Cl(n)-d(8), n = 1,2). The X-ray structure of 6MeCl(2) was obtained on a single-crystal at 160 K. When only 2 equiv. of HSiMe(2)Cl were added, the ethylene(silyl) complex RuH(SiMe(2)Cl)(C(2)H(4))(PCy(3))(2) (7Me(2)Cl) was obtained in addition to the organic products resulting from catalytic hydrogenation, hydrosilylation and dehydrogenative silylation, i.e. C(2)H(6) (major one), C(2)H(3)SiMe(2)Cl and C(2)H(5)SiMe(2)Cl. In the case of 2 equiv. of HSiMeCl(2), upon ethylene addition, 7MeCl(2) was formed in minority compared to a new disilyl complex Ru(SiMeCl(2))(2)(PCy(3))(2) (8MeCl(2)) characterised by NMR spectroscopy and X-ray diffraction on a single crystal at 160 K. In 8MeCl(2), a formal 14-electron species, stabilisation through two agostic C-H bonds of the cyclohexyl groups was ascertained by DFT calculations.

Iron nanoparticle growth in organic superstructures.

A tunable synthesis of iron nanoparticles (NPs) based on the decomposition of {Fe[N(SiMe(3))(2)](2)}(2) in the presence of organic superstructures composed of palmitic acid and hexadecylamine is reported. Control of the size (from 1.5 to 27 nm) and shape (spheres, cubes, or stars) of the NPs has been achieved. An environment-dependent growth model is proposed on the basis of results obtained for the NP morphology under various conditions and a complete Mossbauer study of the colloid composition at different reacting stages. It involves (i) an anisotropic growth process inside organic superstructures, leading to monocrystalline cubic NPs, and (ii) isotropic growth outside these superstructures, yielding polycrystalline spherical NPs.

Experimental and theoretical examination of C-CN and C-H bond activations of acetonitrile using zerovalent nickel.

Experimental and density functional theory show that the reaction of acetonitrile with a zerovalent nickel bis(dialkylphosphino)ethane fragment (alkyl = methyl, isopropyl) proceeds via initial exothermic formation of an eta(2)-nitrile complex. Three well-defined transition states have been found on the potential energy surface between the eta(2)-nitrile complex and the activation products. The lowest energy transition state is an eta(3)-acetonitrile complex, which connects the eta(2)-nitrile to a higher energy eta(3)-acetonitrile intermediate with an agostic C-H bond, while the other two lead to cleavage of either the C-H or the C-CN bonds. Gas-phase calculations show C-CN bond activation to be endothermic, which contradicts the observation of thermal C-CN activation in THF. Therefore, the effect of solvent was taken into consideration by using the polarizable continuum model (PCM), whereupon the activation of the C-CN bond was found to be exothermic. Furthermore the C-CN bond activation was found to be favored exclusively over C-H bond activation due to the strong thermodynamic driving force and slightly lower kinetic barrier.

Photochemical oxidative addition of B-H bonds at ruthenium and rhodium.

Metal phosphine hydrides of type RuP(4)H(2) and RhP(3)H(3) react photochemically with HB(pin)(pin = pinacolate) to form metal boryl hydride complexes via 16-electron intermediates generated by H(2) loss; the second order rate constants for reaction of the intermediates with HB(pin) are even larger than those for reaction with Et(3)SiH.

Mechanistic studies on ethylene silylation with chlorosilanes catalysed by ruthenium complexes.

Silylation of ethylene by chlorosilanes is catalysed by ruthenium complexes. Mechanistic investigations reveal the presence of a complicated network of reactions leading to new sigma-silane, ethylene and silyl complexes.