Synthesis of MnP nanocrystals by treatment of metal carbonyl complexes with phosphines: a new, versatile route to nanoscale transition metal phosphides

The reaction of Mn2(CO)10 with P(SiMe3)3 in coordinating solvents at T >/= 220 degrees C yields low polydispersity, highly crystalline MnP nanoparticles for the first time. The effect of dimensional limiting has resulted in the stabilization of a ferromagnetic ground state at low temperatures, rather than the metamagnetic state observed in bulk (microcrystalline) MnP. The synthetic methodology reported here is demonstrated to be general for a number of different metals and phosphine sources.     

Synthesis of nanoscale nickel(II) and cobalt(II) sulfides

Ranges of stability and regions of the stoichiometric stability of sulfide phases of nickel(II) and cobalt(II) are determined in water–salt solutions. Regions of the homogeneity of NiS and CoS monosulfides are considered. The composition of a microemulsion used as a nanoreactor for synthesizing sulfides is determined, and its phase diagram is plotted. The results from estimating the size of the obtained nanocrystals are presented.     

Simple unprecedented conversion of phosphine oxides and sulfides to phosphine boranes using sodium borohydride

A variety of phosphine oxides and sulfides can be efficiently converted directly to the corresponding phosphine boranes using oxalyl chloride followed by sodium borohydride. Optically active P-stereogenic phosphine oxides can be converted stereospecifically to phosphine boranes with inversion of configuration by treatment with Meerwein's salt followed by sodium borohydride.     

A new reduction route for the synthesis of nanoscale metals and metal oxides with ascorbic acid at low temperature

Reduction of the transition metal complexes in aqueous solution has been investigated systematically by ascorbic acid as the reducing agent without the assistance of any surfactant. Nanoparticles of α-Mn₂O₃, Ag and Cu were synthesized directly through aqueous phase reduction at room temperature. Nanoscale metal oxides such as Co₃O₄, α-Fe₂O₃ and MoO₂ were obtained through ascorbic acid reduction in alkali medium at 40°C. All the products were characterized on their structure and micro-morphology by the X-ray diffraction (XRD) and atomic force microscopy (AFM). The particle size of metal and metal oxides was about 10–50 nm. The reaction details and features were described and discussed.     

Solution processed transition metal sulfides: application as counter electrodes in dye sensitized solar cells (DSCs)

A solution processed method for fabricating transition metal sulfides on fluorine doped tin oxide (FTO) as efficient counter electrodes in iodine/iodide based solar cells has been demonstrated. Conversion efficiencies of 7.01% and 6.50% were obtained for nickel and cobalt sulfides, respectively, comparable to the conventional thermally platinised FTO electrodes (7.32%). A comparable charge transfer resistance of Ni(3)S(2) and Co(8.4)S(8) to conventional Pt was found to be a key factor for such high efficiencies. Cyclic voltammetry, Kelvin probe microscopy, Electrochemical Impedance Spectroscopy, and Tafel polarization were performed to study the underlying reasons behind such efficient counter electrode performance.     

Hollow nanoparticles of metal oxides and sulfides: fast preparation via laser ablation in liquid

In this work, diverse hollow nanoparticles of metal oxides and sulfides were prepared by simply laser ablating metal targets in properly chosen liquids. The Kirkendall voiding and the selective heating with an infrared laser were shown to work as two independent mechanisms for the formation of such hollow nanoparticles in only one- or two-step synthesis approaches. One of the prepared materials, ZnS hollow nanoparticles, showed high performance in gas sensing. The simple, fast, inexpensive technique that is proposed demonstrates very promising perspectives.     

New reactivity patterns of copper(I) and other transition metal NHC complexes: application to ATRC and related reactions

Pre-formed transition metal-NHC complex is shown to be an effective catalyst for Atom Transfer Radical Cyclisation (ATRC) reactions.     

Thermal studies of the reactions of vanadium(V) oxide with other transition metal oxides

Studies of the thermal behaviour of binary oxide mixtures containing vanadium(V) oxide (V₂O₅-TiO₂, V₂,O₅- MoO₃, V₂,O₅-ZrO₂ and V₂O₅-ZnO) have shown that the evolution of gaseous oxygen at fairly low temperatures is characteristic of those systems which are eflective catalysts for the oxidation of hydrocarbons. No weight changes were observed with V₂, O₅-ZnO mixtures under these conditions and, in accordance with this, zinc(II) oxide does not enhance the catalytic activity of vanadium(V) oxide. In V₂O₅-containing systems, evolution of oxygen occurs during the reduction of V₂O₅ to V₂O₄. This process is accelerated in the presence of certain metal oxides and such acceleration may be caused by structural interactions at the interface of the oxides. Among the systems studied, the formation of compounds such as Mo₆V₉O₄₀ is thought to be of little significance from the catalytic point of view.

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Zusammenfassung Die Untersuchung des thermischen Verhaltens vanadium(V)-oxid-haltiger binärer Mischungen (V₂O₅-TiO₂, V₂O₅-MoO₃, V₂O₅-ZrO₂ und V₂O₅-ZnO) ergab, daß die Entwicklung gasförmigen Sauerstoffs bei niedrigen Temperaturen für jene Systeme, welche effektive Katalysatoren der Oxidierung von Kohlenwasserstoffen sind, charakteristisch ist. Keine Gewichtsänderungen wurden bei Mischungen von V₂O₅-ZnO unter diesen Bedingungen beobachtet und dementsprechend fördert Zink(II) Oxid die katalytische Aktivität von Vanadium(V) Oxid nicht. In V₂O₅-haltigen Systemen erfolgt die Sauerstoffentwicklung während der Reduktion von V₂O₅ zu V₂O₄. Dieser Vorgang wird durch die Anwesenheit gewisser Metalloxide beschläunigt und kann durch strukturelle Wechselwirkungen an der Grenzfläche der Oxide gedeutet werden. Bei den untersuchten Systemen wird die Bildung von Verbindungen wie Mo₆V₉O₄₀ vom Gesichtspunkt der Katalyse als wenig bedeutend betrachtet.

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Résumé L'étude du comportement thermique de mélanges d'oxydes binaires contenant de l'oxyde de vanadium(V) (V₂O₅-TiO₂, V₂O₅-MoO₃, V₂O₅-ZrO₂ et V₂O₅-ZnO) a montré que le dégagement de gaz oxygène à température relativement faible est caractéristique des systèmes qui sont des catalyseurs actifs de l'oxydation des hydrocarbures. Avec les mélanges V₂,O₅-ZnO, on n'a pas observé de variations pondérales dans les mêmes conditions et, en accord avec l'observation faite, l'oxyde de zinc(II) n'augmente pas l'activité catalytique de l'oxyde de vanadium(V). Dans les systèmes contenant V₂O₅, le dégagement d'oxygène a lieu au cours de la réduction de V₂O₅ en V₂,O₄. Cette réaction est accélérée en présence de certains oxydes métalliques. Le phénomène d'accélération peut être dû à des interactions structurales à l'interface des oxydes. Dans les systèmes étudiés, la formation de composés comme Mo₆V₉O₄₀ est considérée de peu d'importance du point de vue catalytique.

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, (V₂O₅-iO₂, V₂O₅-₃, V₂O₅-ZrO₂ V₂O₅-ZnO), , , . V₂O₅-ZnO , , () . , , V₂O₅ V₂O₄. . Mo₆V₉O₄₀ , .

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The authors would like to thank Dr. D. J. Cole for carrying out the experimental work.     

Characterization of the redox-reactivity of transition metal oxides by temperature-programmed limited thermal decomposition (TPLTD)

The concept of labile lattice oxygen (LLO) as a consequence of the Mars-Van Krevellen model was reminded, and contrasted with the surface oxygen species. Methods of characterizing of the Me-O bond strength were reviewed emphasizing the temperature-programmed limited thermal decomposition (TPLTD). A series of Ag_xV₂Mo_yO_z was characterized by TPLTD. Two forms of LLO were distinguished. The weaker form is independent on Ag-doping, in contrast to the stronger one. Activation energy of TPLTD of the stronger bound LLO was a linear function of the anion vacancy concentration.

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Zusammenfassung Aus dem Konzept des labilen Gittersauerstoffs (LLO) als Konsequenz des Mars-Van Krevellen-Modells wird die Rolle der Oberflächen-Sauerstoff-Spezies hervorgehoben. Ein Überblick über die Methoden zur Charakterisierung der Me-O-Bindung wird unter besonderer Betonung der temperaturprogrammierten begrenzten thermischen Zersetzung (TPLTD) gegeben.Eine Reihe Ag _x V₂Mo _y O₂ wurde mittels TPLTD charakterisiert, dabei konnten zwei Arten von LLO unterschieden werden. Die schwächere Form ist im Gegensatz zu der stärkeren unabhängig vom Silbergehalt. Die Aktivierungsenergie der TPLTD der stärker gebundenen LLO hängt linear von der Konzentration der Anionenfehlstellen ab.

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, - , . Me- . Ag_xV₂Mo_yO_z, . , , . n.

     

Di- and poly-nuclear transition metal complexes as catalysts for the metal carbonyl substitution reaction. The role of supported metals and metal oxides as catalyst promoters

Various di- and poly-nuclear transition metal complexes have been investigated as catalysts for the metal carbonyl substitution reaction. The complexes [{(η⁵-C₅H₄R)Fe(CO)₂} ₂] (R = H, Me, CO₂Me, OMe, O(CH₂)₄OH) and [{(η⁵-C₅H₅)-Ru(CO)₂} ₂] are active catalysts for a range of substitution reactions including the probe reaction [Fe(CO)₄(CNBu^t)] + Bu^tNC → [Fe(CO)₃(CNBu^t)₂] + CO. [{(η⁵-C₅Me₅)Fe(CO)₂}₂] is catalytically active only on irradiation with visible light. For [{η⁵-C₅H₅)Fe(CO)₂}₂] and a range ofisocyanides RNC ( R = Bu^t, C₆H₅CH₂, 2,6-Me₂C₆H₃), catalyst modification by substitution with isocyanide is a major factor influencing the degree of the catalytic effects observed, e.g. [{(η⁵-C₅H₅)Fe(CO)(CNBu^t)}₂] is approximately 35 times as active as [(η⁵-C₅H₅)₂FE₂(CO)₃(CNBu^t)] for the [Fe(CO)₄(CNBu^t)] → [Fe(CO)₃(CNBu^t)₂] conversion. Mechanistic studies on this system suggest that the catalytic substitution step probably involves a rapid intermolecular attack of isonitrile, possibly on a labile catalyst-substrate radical intermediate such as {[Fe(CO)₄(CNR)][(η⁵-C₅H₅)Fe(CO)₂]}; or on a reactive radical cation such as [Fe(CO)₄(CNR)]⁺ generated via electron transfer between the substrate and the catalyst. Other transition metal complexes which also catalyze the substitution of CO by isocyanide in [Fe(CO)₄(CNR)] (and [M(CO)₆] (M = Cr, Mo, W), [Mn₂(CO)₁₀], [Re₂(CO)₁₀]) include [Ru₃(CO)₁₂], [H₄Ru₄(CO)₁₂], [M₄(CO)₁₂] (M = Co, Ir) and [Co₂(CO)₈]. These reactions conform to the general mechanistic patterns established for [{(η⁵-C₅H₅)Fe(CO)₂}₂], suggesting a similar mechanism. A range of materials, notably PtO₂, PdO and Pd/C, act as promoters for the homogeneous di- and poly-nuclear transition metal catalysts, and can even be used to induce activity in normally inactive dimer and cluster complexes e.g. [Os₃(CO)₁₂]. This promotion is attributed to at least three possible effects: the removal of catalyst inhibitors, a catalyzed substitution of the homogeneous catalyst partner, and a possible homogeneous-heterogeneous interaction which promotes the formation of catalytic intermediates.     

On surface states of transition metal carbides,nitrides, and oxides: (001), (011), and (111) surfaces

The simple semiquantitative approach to the calculation of the energy of surface states, proposed recently by the authors, is applied to high-symmetry surfaces of selected transition metal carbides, nitrides, and oxides. The results are compared with recent experimental and theoretical data. The necessity to include the changes in the potential at the crystal surface is indicated.     

Adsorption of enterobactin to metal oxides and the role of siderophores in bacterial adhesion to metals

The potential contribution of chemical bonds formed between bacterial cells and metal surfaces during biofilm initiation has received little attention. Previous work has suggested that bacterial siderophores may play a role in bacterial adhesion to metals. It has now been shown using in situ ATR-IR spectroscopy that enterobactin, a catecholate siderophore secreted by Escherichia coli, forms covalent bonds with particle films of titanium dioxide, boehmite (AlOOH), and chromium oxide-hydroxide which model the surfaces of metals of significance in medical and industrial settings. Adsorption of enterobactin to the metal oxides occurred through the 2,3-dihydroxybenzoyl moieties, with the trilactone macrocycle having little involvement. Vibrational modes of the 2,3-dihydroxybenzoyl moiety of enterobactin, adsorbed to TiO(2), were assigned by comparing the observed IR spectra with those calculated by the density functional method. Comparison of the observed adsorbate IR spectrum with the calculated spectra of catecholate-type [H(2)NCOC(6)H(3)O(2)Ti(OH)(4)](2-) and salicylate-type [H(2)NCOC(6)H(3)O(2)HTi(OH)(4)](2-) surface complexes indicated that the catecholate type is dominant. Analysis of the spectra for enterobactin in solution and that adsorbed to TiO(2) revealed that the amide of the 2,3-dihydroxybenzoylserine group reorientates during coordination to surface Ti(IV) ions. Investigation into the pH dependence of enterobactin adsorption to TiO(2) surfaces showed that all 2,3-dihydroxybenzoyl groups are involved. Infrared absorption bands attributed to adsorbed enterobactin were also strongly evident for E. coli cells attached to TiO(2) particle films. These studies give evidence of enterobactin-metal bond formation and further suggest the generality of siderophore involvement in bacterial biofilm initiation on metal surfaces.     

Bis(pyrene)metal complexes of vanadium,niobium and titanium: isolable homoleptic pyrene complexes of transition metals

Reduction of VCl₃(THF)₃ (THF is tetrahydrofuran) and NbCl₄(THF)₂ by alkali metal pyrene radical anion salts in THF affords the paramagnetic sandwich complexes bis[(1,2,3,3a,10a,10b‐η)‐pyrene]vanadium(0), [V(C₁₆H₁₀)₂], and bis[(1,2,3,3a,10a,10b‐η)‐pyrene]niobium(0), [Nb(C₁₆H₁₀)₂]. Treatment of tris(naphthalene)titanate(2−) with pyrene provides the isoelectronic titanium species, isolated as an (18‐crown‐6)potassium salt, namely catena‐poly[[(18‐crown‐6)potassium]‐μ‐[(1,2‐η:1,2,3,3a,10a,10b‐η)‐pyrene]‐titanate(−I)‐μ‐[(1,2,3,3a,10a,10b‐η:6,7‐η)‐pyrene]], {[K(C₁₂H₂₄O₆)][Ti(C₁₆H₁₀)₂]}_n. The first two compounds have very similar packing, with neighboring molecules arranged orthogonally to one another, such that aromatic donor–acceptor interactions are likely responsible for the specific arrangement. The asymmetric unit contains a half‐occupancy metal center η⁶‐coordinated to one pyrene ligand, with the full M(pyrene)₂ molecule generated by a crystallographic inversion center. In the titanium compound, the cations and anions are in alternating contact throughout the crystal structure, in one‐dimensional chains along the [101] direction. As in the other two compounds, the asymmetric unit contains a half‐occupancy Ti atom η⁶‐coordinated to one pyrene ligand. Additionally, the asymmetric unit contains one half of an (18‐crown‐6)potassium cation, located on a crystallographic inversion center coincident with the K atom. The full formula units are generated by those inversion centers. In all three structures, the pyrene ligands are eclipsed and sandwich the metals in one of two inversion‐related sites. These species are of interest as the first isolable homoleptic pyrene transition metal complexes to be described in the scientific literature.     

Organometallic polymers. I. Synthesis of ferrocene-containing poly(phosphine oxides) and poly(phosphine sulfides)

Poly(phosphine oxides) and poly(phosphine sulfides) of ferrocene were synthesized in the melt phase. The resulting ferrocene polymers, linked by phosphorus bridges, were thermally stable and infusible solids, of low molecular weight (M?_n < 4000). Phenyldichlorophosphine, phenyldichlorophosphonate, and phenylphosphonothioic dichloride were copolymerized with ferrocene in the melt phase (80–110°C.) with ZnCl₂ as a catalyst. As the polymerization temperature was raised, cleavage of cyclopentadiene rings from iron became more pronounced, and cyclopentane-bridged polymers of ferrocene were produced in competition with the ferrocene–phosphorus polymers. The cleavage-polymerization process became predominant at 140°C. The structures of poly(phosphine oxides) (and sulfides) of ferrocene were verified by infrared and nuclear magnetic resonance spectroscopy.     

Organometalloidal derivatives of the transition metals : V. A 1,2-alkyl shift from lead to a transition metal

The complexes (η⁵-C₅H₅)Fe(CO)₂PbR₃ (R = Me and Et) have been synthesized and characterized. The trimethyllead complex is extremely labile with respect to thermal and photochemical decomposition that leads to the formation of (Me)₄Pb, Pb, and (η⁵-C₅H₅)Fe(CO)₂Me. This new type of methyl transfer from Pb to Fe does not occur for the triethyllead complex thermally, but does occur to a limited extent photochemically, and helps explain certain zinc treatments for removal of organolead compounds from industrial effluents.     

Polarity and structure of P(X)-modified (X = O,S) arylcarbamoylmethylphosphine oxides and sulfides

As shown by the dipole moment method and quantum chemical calculations, (arylcarbamoylmethyl) diphenylphosphine oxides and sulfides exist as equilibrium mixtures of several rotational isomers stabilized by H · · · X intramolecular hydrogen bonds (X = O, S). The most energetically favorable rotamer and its fraction have been determined for each compound.