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[Fe.sub.x][Rh.sub.100-x] (x = 50, 80) nanoparticles (NPs) with an average diameter of ~2 nm were prepared by simultaneous decomposition of stoichiometric quantities of Fe[[N[(Si[([CH.sub.3]).sub.3]).sub.2])].sub.2] and Rh[([C.sub.3][H.sub.5]).sub.3] using two different routes: 1) a standard hydrogenation procedure and 2) a new one based on use of amino-borane as a reducing agent. All samples were found to be superparamagnetic with a blocking temperature below 10 K. Results of X-Ray magnetic circular dichroism (XMCD) experiments at the Fe K-edge and the Rh [L.sub.2,3] edges have shown that not only iron but also rhodium atoms are magnetic as a result of hybridization of Fe 3d states with 4d states of Rh. The total induced magnetic moment of Rh atoms as well as its spin and orbital contributions are shown to depend on chemical composition of [NP.sub.S] and the preparation method. Index Terms--Induced magnetic moment, magnetic nanoparticles, X-ray magnetic circular dichroism.

Nanoparticles of nickel have been obtained in solution through reaction of an organometallic precursor, Ni(COD)(sub 2) (COD=cycloocta-1, 5-diene), with dihydrogen, in the presence of various stabilizing agents. This stabilizing agent was selected for the production of nickel anorods, and the influence of ligands on the effective anisotropy is discussed.

The synthesis of CoxRh(sub 1-x) and CoxRu(sub 1-x) alloys of nanometric size dispersed in a polymer matrix through the simultaneous decomposition of the organometallic precursors in solution in mild conditions is described. These structural studies enable to find some analogies between three CoM systems (M= Ru, Rh, Pt).

It has been possible to demonstrate the synthesis of CoxPt1-x particles of nanometric size dispersed in an inert organic matrix through the simultaneous decomposition of the organometallic precursors Co(eta3-C8H13)(eta4-C8H12) and Pt2(dba)3 in solution in mild conditions.

Nanoparticles of nickel have been obtained in solution through reaction of an organometallic precursor, Ni(COD)[sub 2] (COD=cycloocta-1,5-diene), with dihydrogen, in the presence of various stabilizing agents. X-ray diffraction studies evidence a face-centered-cubic structure for all samples. Spherical isolated superparamagnetic nanoparticles (d∼4.5 nm) are produced in the presence of poly(N-vinylpyrrolid-2-one). They display a magnetization value comparable to that of bulk nickel, as determined from superconducting quantum iinterference device (SQUID) measurements. Exposure of the surface of the nanoparticles to CO, leading to CO coordination as monitored by infrared spectroscopy, or to methanol, strongly reduces their magnetization. This reduction corresponds respectively to one or two magnetically inactive layers of nickel atoms at the nanoparticles surface. The production of elongated nanoparticles was favored when either trioctylphosphineoxide or hexadecylamine (HDA) were used as stabilizing agents. In this case, SQUID measurements show that only HDA preserves the magnetization of the surface. This stabilizing agent was selected for the production of nickel nanorods. The influence of ligands on the effective anisotropy is discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of nanoparticles (NPs) with magnetic properties close to those of bulk are described by using superconducting quantum interference device (SQUID) and Mossbauer measurements. The magnetic anisotropy energy constant has increased up to ten times the bulk one.

A porous Ru nanomaterial exhibits high electrocatalytic performance and excellent durability for the hydrogen evolution reaction (HER) under both acidic and neutral conditions. It displays a low overpotential of 83 mV at a current density of 10 mA cm−2 and an excellent durability up to 12 h in 0.5 M H2SO4. [ABSTRACT FROM AUTHOR]

A variety of imaging technologies are now routinely used in the medical field, their use being continuously enlarged through the development of contrast agents. Recently nanoparticles (NPs) proved efficient to improve imaging in vivo by increasing contrast and targeting capabilities. The current trend is now focused on the development of dual contrast agents combining two or more functionalities on the same NP. Motivated by this new challenge we developed FeBi NPs as new nanomaterials with potential application as a contrast agent for MRI and CT imaging. In addition to the well-known use of iron in the development MRI contrast agents, we chose Bi as a CT imaging agent rather than the more documented gold, because it possesses a larger X-ray attenuation coefficient and is much less expensive. Two sets of NPs, with sizes around 150 nm and 14 nm, were synthesized using organometallic approaches. In both cases, the NPs are spherical, and contain distinct domains of Fe and Bi, with the surface being enriched with Fe, and a hydrophobic coating. This coating differs from one sample to the other: the surfaces of the 150 nm large NPs are coated by amine ligands, while those of the 14 nm large NPs are coated by a mixture of an amine and its hydrochloride salt. Exchange of the surface ligands to afford water soluble NPs has been attempted. We show that only the larger NPs could be functionalized with water soluble ligands, which is in agreement with the lability of their initial surface coating. Colloidal aqueous solutions of FeBi NPs with glycoPEG ligands have been obtained. [ABSTRACT FROM AUTHOR]

Nanoparticles can be synthesized from metal-organic or organometallic precursors, either by classical thermal decomposition, ultrasound activation, photolysis as well as hydrogenation or hydrolysis reactions. The size, size distribution and more importantly surface state of these nanoparticles are much better controlled than when they are produced by chemical or electrochemical reduction of metal salts. Hence, metal or oxide nanoparticles can be obtained that are suitable for fundamental physics at the nanoscale, especially for magnetic studies. This is currently of particular interest as many applications require systems of still smaller sizes, the properties of which are not yet fully understood. [ABSTRACT FROM AUTHOR]

Monodisperse FeCo nanoparticles were synthesized via thermal decomposition of appropriate organometallic complexes in heated toluene containing surfactants, aiming to a soft magnetic nanomaterial with a high metal percent. The particles were characterized by X-ray powder diffraction, electron microscopy, and static magnetometry techniques. The effect of air exposure on the structural and magnetic properties was examined. Portions of the dried nanoparticles were mixed with additional surfactants or polyvinylpyrrolidone, followed by redispersion into tetrahydrofuran, so as to study arrangement features in the first case, while the use of polyvinylpyrrolidone intended to the expansion of the interparticle distances in order to get more "isolated" nanoparticles. [ABSTRACT FROM AUTHOR]

CoRh alloy nanoparticles (NPs) show nontrivial correlations between chemical and magnetic order that lead to a remarkable nonmonotonous dependence of the magnetic anisotropy energy as a function of composition. Combining experiment and theory we demonstrate how the induced 4d moments and the 3d-4d interfaces control the magnetoanisotropic behavior. New possibilities of tailoring the magnetic characteristics of NPs are thus opened. [ABSTRACT FROM AUTHOR]

The magnetic remanent states of 4-nm-diameter single-crystalline Co nanowires are characterized using off-axis electron holography. Measurements are obtained from isolated wires, as well as from bundles of wires and "multibranch" wires joined by 15-nm-diameter nodes of Co. The fraction of magnetically active moments in a single 4-nm-diameter wire is measured to be 1.01±0.19, indicating that, to within experimental error, the wire is fully magnetized throughout its diameter. [ABSTRACT FROM AUTHOR]

Ultrafine cobalt particles have been reproducibly synthesized by decomposition of an organometallic precursor in the presence of a stabilizing polymer. The size of the stable monodisperse colloids thus obtained is seen to strongly depend on the nature of the polymer: around 4.2 nm diameter in polyphenylenoxide (PPO) and around 1.4 nm diameter in polyvinylpyrrolidone (PVP). Investigations by wide angle x-ray scattering (WAXS) and high-resolution transmission electron microscopy (HRTEM) give evidence for a size dependence of the structural organization, and hence for a close relationship between structure and synthesis conditions. Co/PPO particles exhibit a hexagonal compact structure with the metal-metal bond length of the bulk material while Co/PVP ones display an original structure. We show that the unusual features of the experimental data in Co/PVP clearly point to a nonperiodic polytetrahedral structure. Successful simulations of the HRTEM and WAXS results have been obtained using models built on the basis of a polytetrahedral arrangement. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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A wide range of nano-objects is found in many applications of our everyday life. Recognition of their peculiar properties and ease of functionalization has prompted their engineering into multifunctional platforms that are supposed to afford efficient tools for the development of biomedical applications. However, bridging the gap between bench to bedside cannot be expected without a good knowledge of their behaviour in vivo, which can be obtained through non-invasive imaging techniques, such as positron emission tomography (PET). Their radiolabelling with [ 18 F]-fluorine, a technique already well established and widely used routinely for PET imaging, with [ 18 F]-FDG for example, and in preclinical investigation using [ 18 F]-radiolabelled biological macromolecules, has, therefore, been developed. In this context, this review highlights the various nano-objects studied so far, the reasons behind their radiolabelling, and main in vitro and/or in vivo results obtained thereof. Then, the methods developed to introduce the radioelement are presented. Detailed indications on the chemical steps involved are provided, and the stability of the radiolabelling is discussed. Emphasis is then made on the techniques used to purify and analyse the radiolabelled nano-objects, a point that is rarely discussed despite its technical relevance and importance for accurate imaging. The pros and cons of the different methods developed are finally discussed from which future work can develop.

The conversion of biomass as a sustainable path to access valuable chemicals and fuels is very attractive for the chemical industry, but catalytic conversions still often rely on the use of noble metals. Sustainability constraints require developing alternative catalysts from abundant and low-cost metals. In this context, NiFe nanoparticles are interesting candidates. In their reduced and supported form, they have been reported to be more active and selective than monometallic Ni in the hydrogenation of the polar functions of organic molecules, and the two metals are very abundant. However, unlike noble metals, Ni and Fe are easily oxidized in ambient conditions, and understanding their transformation in both oxidative and reductive atmospheres is an important though seldom investigated issue to be addressed before their application in catalysis. Three types of NiFe nanoparticles were prepared by an organometallic approach to ensure the formation of ultrasmall nanoparticles (<3.5 nm) with a narrow size distribution, controlled composition and chemical order, while working in mild conditions: Ni2Fe1 and Ni1Fe1, both with a Ni rich core and Fe rich surface, and an alloy with a Ni1Fe9 composition. Supported systems were obtained by the impregnation of silica with a colloidal solution of the preformed nanoparticles. Using advanced characterization techniques, such as wide-angle X-ray scattering (WAXS) and X-ray absorption spectroscopy (XAS) in in situ conditions, this study reports on the evolution of the chemical order and of the oxidation state of the metals upon exposure to air, hydrogen, and/or increasing temperature, all factors that may affect their degree of reduction and subsequent performance in catalysis. We show that if oxidation readily occurs upon exposure to air, the metals can revert to their initial state upon heating in the presence of H 2 but with a change in structure and chemical ordering.

Production of hydrogen from a renewable source that is water requires the development of sustainable catalytic processes. This implies, among others, developing efficient catalytic materials from abundant and low-cost resources and investigating their performance, especially in the oxidation of water as this half-reaction is the bottleneck of the water splitting process. For this purpose, NiFe-based nanoparticles with sizes ca . 3-4 nm have been synthesized by an organometallic approach and characterized by complementary techniques (WAXS, TEM, STEM-HAADF, EDX, XPS, and ATR-FTIR). They display a Ni core and a mixed Ni-Fe oxide shell. Once deposited onto FTO electrodes, they have been assessed in the electrocatalytic oxygen evolution reaction under alkaline conditions. Three different Ni/Fe ratios (2/1, 1/1 and 1/9) have been studied in comparison with their monometallic counterparts. The Ni2Fe1 nanocatalyst displayed the lowest overpotential (320 mV at j = 10 mA cm -2 ) as well as excellent stability over 16 h.

Magnetic resonance imaging, MRI, relying on 19 F nuclei has attracted much attention, because the isotopes exhibit a high gyromagnetic ratio (comparable to that of protons) and have 100% natural abundance. Furthermore, due to the very low traces of intrinsic fluorine in biological tissues, fluorine labeling allows easy visualization in vivo using 19 F-based MRI. However, one of the drawbacks of the available fluorine tracers is their very limited solubility in water. Here, we detail the design and preparation of a set of water-compatible fluorine-rich polymers as contrast agents that can enhance the effectiveness of 19 F-based MRI. The agents are synthesized using the nucleophilic addition reaction between poly(isobutylene- alt -maleic anhydride) copolymer and a mixture of amine-appended fluorine groups and polyethylene glycol (PEG) blocks. This allows control over the polymer architecture and stoichiometry, resulting in good affinity to water solutions. We further investigate the effects of introducing additional segmental mobility to the fluorine moieties in the polymer, by inserting a PEG linker between the moieties and the polymer backbone. We find that controlling the polymer stoichiometry and introducing additional segmental mobility enhance the NMR signals and narrow the peak profile. In particular, we assess the impact of the PEG linker on T 2 * and T 1 relaxation times, using a series of gradient-recalled echo images with varying echo times, TE, or recovery time, TR, respectively. We find that for equivalent concentrations, the PEG linker greatly increases T 2 *, while maintaining high T 1 values, as compared to polymers without this linker. Phantom images collected from these compounds show bright signals over a background with high intensities.

The present environmental crisis prompts the search for renewable energy sources such as solar-driven production of hydrogen from water. Herein, we report an efficient hybrid photocatalyst for water oxidation, consisting of a ruthenium polypyridyl complex covalently grafted on core/shell Fe@FeO x nanoparticles via a phosphonic acid group. The photoelectrochemical measurements were performed under 1 sun illumination in 1 M KOH. The photocurrent density of this hybrid photoanode reached 20 μA/cm 2 (applied potential of +1.0 V vs reversible hydrogen electrode), corresponding to a turnover frequency of 0.02 s -1 . This performance represents a 9-fold enhancement of that achieved with a mixture of Fe@FeO x nanoparticles and a linker-free ruthenium polypyridyl photosensitizer. This increase in performance could be attributed to a more efficient electron transfer between the ruthenium photosensitizer and the Fe@FeO x catalyst as a consequence of the covalent link between these two species through the phosphonate pendant group.

To shed light on the factors governing the stability and surface properties of iron nanoparticles, a series of iron nanoparticles has been produced by hydrogenation of two different iron amido complexes: the bis[bis(trimethylsilyl)amido] Fe(ii), [Fe(N(SiMe 3 ) 2 ) 2 ] 2 , and the bis(diphenylamido) Fe(ii), [Fe(NPh 2 ) 2 ]. Nanostructured materials of bcc structure, or nanoparticles displaying average sizes below 3 nm and a polytetrahedral structure, have been obtained. Depending on the synthesis conditions, the magnetization of the nanoparticles was either significantly lower than that of bulk iron, or much higher as for clusters elaborated under high vacuum conditions. Unexpectedly, hydrogenation of aromatic groups of the ligands of the [Fe(NPh 2 ) 2 ] precursor has been observed in some cases. Confrontation of the experimental results with DFT calculations made on polytetrahedral Fe 91 model clusters bearing hydrides, amido and/or amine ligands at their surface, has shown that amido ligands can play a key role in the stabilisation of the nanoparticles in solution while the hydride surface coverage governs their surface magnetic properties. This study indicates that magnetic measurements give valuable indicators of the surface properties of iron nanoparticles in this size range, and beyond, of their potential reactivity., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Production of formate via CO2/bicarbonate hydrogenation using cheap metal-based heterogeneous catalysts is attractive. Herein, we report the organometallic synthesis of a foam-like Ni@Ni(OH)2 composite nanomaterial which exhibited remarkable air stability and over 2 times higher catalytic activity than commercial RANEY® Ni catalyst in formate synthesis. Formate generation was achieved with an optimal rate of 6.0 mmol gcat-1 h-1 at 100 °C, a significantly lower operation temperature compared to the 200-260 °C reported in the literature. Deep characterization evidenced that this nanomaterial was made of an amorphous Ni(OH)2 phase covering metallic Ni sites; a core-shell structure which is crucial for the stability of the catalyst. The adsorption of bicarbonates onto the Ni@Ni(OH)2 catalyst was found to be a kinetically relevant step in the reaction, and the Ni-Ni(OH)2 interface was found to be beneficial for both CO2 and H2 activation thanks to a cooperative effect. Our findings emphasize the underestimated potential of Ni-based catalysts in CO2 hydrogenation to formate, indicating a viable strategy to develop stable, cheap metal catalysts for greener catalytic applications.

The growing concern over the toxicity of Gd-based contrast agents used in magnetic resonance imaging (MRI) motivates the search for less toxic and more effective alternatives. Among these alternatives, iron-iron oxide (Fe@FeOx) core-shell architectures have been long recognized as promising MRI contrast agents while limited information on their engineering is available. Here we report the synthesis of 10 nm large Fe@FeOx nanoparticles, their coating with a 11 nm thick layer of dense silica and functionalization by 5 kDa PEG chains to improve their biocompatibility. The nanomaterials obtained have been characterized by a set of complementary techniques such as infra-red and nuclear magnetic resonance spectroscopies, transmission electron microscopy, dynamic light scattering and zetametry, and magnetometry. They display hydrodynamic diameters in the 100 nm range, zetapotential values around -30 mV, and magnetization values higher than the reference contrast agent RESOVIST ® . They display no cytotoxicity against 1BR3G and HCT116 cell lines and no hemolytic activity against human red blood cells. Their nuclear magnetic relaxation dispersion (NMRD) profiles are typical for nanomaterials of this size and magnetization. They display high r 2 relaxivity values and low r 1 leading to enhanced r 2 /r 1 ratios in comparison with RESOVIST ® . All these data make them promising contrast agents to detect early stage tumors., Competing Interests: The authors declare no conflict of interest.

Given that the properties of metal nanoparticles (NPs) depend on several parameters (namely, morphology, size, surface composition, crystalline structure, etc.), a computational model that brings a better understanding of a structure-property relationship at the nanoscale is a significant plus in order to explain the surface properties of metal NPs and also their catalytic viability, in particular, when envisaging a new stabilizing agent. In this study we combined experimental and theoretical tools to obtain a mapping of the surface of ruthenium NPs stabilized by ethanoic acid as a new capping ligand. For this purpose, the organometallic approach was applied as the synthesis method. The morphology and crystalline structure of the obtained particles was characterized by state-of-the art techniques (TEM, HRTEM, WAXS) and their surface composition was determined by various techniques (solution and solid-state NMR, IR, chemical titration, DFT calculations). DFT calculations of the vibrational features of model NPs and of the chemical shifts of model clusters allowed us to secure the spectroscopic experimental assignations. Spectroscopic data as well as DFT mechanistic studies showed that ethanoic acid lies on the metal surface as ethanoate, together with hydrogen atoms. The optimal surface composition determined by DFT calculations appeared to be ca. [0.4-0.6] H/Rusurf and 0.4 ethanoate/RuSurf, which was corroborated by experimental results. Moreover, for such a composition, a hydrogen adsorption Gibbs free energy in the range -2.0 to -3.0 kcal mol-1 was calculated, which makes these ruthenium NPs a promising nanocatalyst for the hydrogen evolution reaction in the electrolysis of water.

Cobalt nanoparticles with different sizes and morphologies including spheres, rods, disks, and hexagonal prisms have been synthesized through the decomposition of the olefinic precursor [Co(η(3)-C8H13)(η(4)-C8H12)] under dihydrogen, in the presence of hexadecylamine and different rhodamine derivatives, or aromatic carboxylic acids. UV-vis spectroscopy, X-ray diffraction, low and high resolution transmission electron microscopy, and electron tomography have been used to characterize the nanomaterials. Especially, the Co nanodisks formed present characteristics that make them ideal nanocrystals for applications such as magnetic data storage. Focusing on their growth process, we have evidenced that a reaction between hexadecylamine and rhodamine B occurs during the formation of these Co nanodisks. This reaction limits the amount of free acid and amine, usually at the origin of the formation of single crystal Co rods and wires, in the growth medium of the nanocrystals. As a consequence, a growth mechanism based on the structure of the preformed seeds rather than oriented attachment or template assisted growth is postulated to explain the formation of the nanodisks.

The control of the metallic nanocrystal shape is of prime importance for a wide variety of applications. We report a detailed research work on metal-organic chemical routes for the synthesis of a highly symmetrical crystal structure. In particular, this study shows the key parameters ensuring the anisotropic growth of nickel nanostructures (fcc crystal). Numerous reaction conditions are investigated (precursors, solvents, temperature, reducing agents, reaction time, and types and ratios of surfactants, such as alkyl amines, carboxylic acids, and phosphine oxides), and their effects on the size and shape of the final product are reported. The role of the growth modifiers and the structuring of the reaction media on the anisotropic growth are demonstrated. This metal-organic approach generates several novel anisotropic nanostructures in a wide size range depending on the reaction conditions. In this way, nanomaterials with reproducible size, shape, and composition are obtained with good yield. Transmission electron microscopy techniques (TEM and HRTEM) are the principal methods for monitoring the morphology.

The effectiveness of amine-borane as reducing agent for the synthesis of iron nanoparticles has been investigated. Large (2-4 nm) Fe nanoparticles were obtained from [Fe{N(SiMe3)2}2]. Inclusion of boron in the nanoparticles is clearly evidenced by extended X-ray absorption fine structure spectroscopy and Mössbauer spectrometry. Furthermore, the reactivity of amine-borane and amino-borane complexes in the presence of pure Fe nanoparticles has been investigated. Dihydrogen evolution was observed in both cases, which suggests the potential of Fe nanoparticles to promote the release of dihydrogen from amine-borane and amino-borane moieties., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We investigate the formation of bi-metallic particles in the Fe-Bi system, well known as totally immiscible in the bulk, using a large combination of structural and element-sensitive techniques, well-adapted to the nanoscale. The synthesis approach makes use of the kinetics of decomposition of the different precursors to achieve a controlled sequential growth of the different elements. Different ligands have also been used in order to limit the size and ensure dispersion of the synthesized particles. Our results give evidence for the presence of body-centered cubic ferromagnetic iron nanograins together with larger bismuth crystallites. Interestingly, while the iron particles remain very small, the resistance to oxidation of the Fe-Bi nanocomposites highly depends on the stabilizing ligand used in the synthesis. The presence of both metals, Fe and Bi, in a single cluster has been clearly revealed in the oxidation resistant composite synthesized using the HMDS ligand.