Showing papers on "Osmium published in 2012"

Dicarba-closo-dodecarborane-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium: biological relevance and synthetic strategies

Abstract: This review describes how the incorporation of dicarba-closo-dodecarboranes into half-sandwich complexes of ruthenium, osmium, rhodium and iridium might lead to the development of a new class of compounds with applications in medicine. Such a combination not only has unexplored potential in traditional areas such as Boron Neutron Capture Therapy agents, but also as pharmacophores for the targeting of biologically important proteins and the development of targeted drugs. The synthetic pathways used for the syntheses of dicarba-closo-dodecarboranes-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium are also reviewed. Complexes with a wide variety of geometries and characteristics can be prepared. Examples of addition reactions on the metal centre, B–H activation, transmetalation reactions and/or direct formation of metal–metal bonds are discussed (103 references).

A SAR Study of Novel Antiproliferative Ruthenium and Osmium Complexes with Quinoxalinone Ligands in Human Cancer Cell Lines

Abstract: A series of ruthenium(II) arene complexes with 3-(1H-benzimidazol-2-yl)-1H-quinoxalin-2-one, bearing pharmacophoric groups of known protein kinase inhibitors, and related benzoxazole and benzothiazole derivatives have been synthesized. In addition, the corresponding osmium complexes of the unsubstituted ligands have also been prepared. The compounds have been characterized by NMR, UV–vis, and IR spectroscopy, ESI mass spectrometry, elemental analysis, and by X-ray crystallography. Antiproliferative activity in three human cancer cell lines (A549, CH1, SW480) was determined by MTT assays, yielding IC50 values of 6–60 μM for three unsubstituted metal-free ligands, whereas values for the metal complexes vary in a broad range from 0.3 to 140 μM. Complexation with osmium of quinoxalinone derivatives with benzimidazole or benzothiazole results in a more consistent increase in cytotoxicity than complexation with ruthenium. For selected compounds, the capacity to induce apoptosis was confirmed by fluorescence mic...

Atomic Layer Deposition of Osmium

Abstract: Growth of osmium thin films and nanoparticles by atomic layer deposition is described. The Os thin films were successfully grown between 325 and 375 °C using osmocene and molecular oxygen as precursors. The films consisted of only Os metal as osmium oxides were not detected in X-ray diffraction measurements. Also the impurity contents of oxygen, carbon, and hydrogen were less than 1 at % each at all deposition temperatures. The long nucleation delay of the Os process facilitates either Os nanoparticle or thin film deposition. However, after the nucleation delay of about 350 cycles the film growth proceeded linearly with increasing number of deposition cycles. Also conformal growth of Os thin films on three-dimensional (3-D) structures was confirmed.

An osmium(III)/osmium(V) redox couple generating Os(V)(O)(OH) center for cis-1,2-dihydroxylation of alkenes with H2O2: Os complex with a nitrogen-based tetradentate ligand.

Abstract: For the synthesis of the 1,2-diols, cis-1,2-dihydroxylation of alkenes catalyzed by osmium(VIII) tetroxide (OsO(4)) is a powerful method. However, OsO(4) is quite toxic due to its highly volatile and sublimable nature. Thus, the development of alternative catalysts for cis-1,2-dihydroxylation of alkenes is highly challenging. Our approach involves the use of a nitrogen-based tetradentate ligand, tris(2-pyridylmethyl)amine (tpa), for an osmium center to develop a new osmium catalyst and hydrogen peroxide (H(2)O(2)) as a cheap and environmentally benign oxidant. The new Os-tpa complex acts as a very efficient turnover catalyst for syn-selective dihydroxylation of various alkenes (turnover number ∼1000) in aqueous media, and H(2)O(2) oxidant is formally incorporated into the products quantitatively (100% atom efficiency). The reaction intermediates involved in the catalytic cycle have been isolated and characterized crystallographically as [Os(III)(OH)(H(2)O)(tpa)](2+) and [Os(V)(O)(OH)(tpa)](2+) complexes. The observed syn-selectivity, structural characteristics of the intermediates, and kinetic studies have suggested a concerted [3 + 2]-cycloaddition mechanism between [Os(V)(O)(OH)(tpa)](2+) and alkenes, which is strongly supported by DFT calculations.

Luminescent bis-tridentate ruthenium(II) and osmium(II) complexes based on terpyridyl-imidazole ligand: synthesis, structural characterization, photophysical, electrochemical, and solvent dependence studies.

Abstract: Homo- and heteroleptic bis-tridentate ruthenium(II) and osmium(II) complexes of compositions [(tpy-PhCH3)Ru(tpy-HImzPh3)](ClO4)2 (1), [(H2pbbzim)Ru(tpy-HImzPh3)] (ClO4)2 (2) and [M(tpy-HImzPh3)2](ClO4)2 [M = RuII (3) and OsII (4)], where tpy-PhCH3 = p-methylphenyl terpyridine, H2pbbzim = 2,6-bis(benzimidazole-2-yl)pyridine and tpy-HImzPh3 = 4′-[4-(4,5-diphenyl-1H-imidazol-2-yl)-phenyl]-[2,2′:6′,2′′]terpyridine, have been synthesized and characterized by using standard analytical and spectroscopic techniques. These compounds were designed to increase the room temperature excited-state lifetimes of bisterpyridine-type ruthenium(II) and osmium(II) complexes. The X-ray crystal structures of two homoleptic complexes 3 and 4 have been determined and show that both the compounds crystallized in orthorhombic form with space group Fddd. The photophysical and redox properties of the complexes have been thoroughly investigated. All the complexes display moderately strong luminescence at room temperature with lifetimes in the range of 6–35 ns. The complexes are found to undergo one reversible oxidation in the positive potential window (0 to +1.6 V) and one irreversible and two successive quasi-reversible reductions in the negative potential window (0 to −2.0 V). The influence of solvents on the photophysical properties of the complexes has also been investigated in detail.

Synthesis of novel Ru2C under high pressure-high temperature conditions.

Abstract: We report here, for the first time, synthesis of the Fe(2)N type hexagonal phase of ruthenium carbide by a high pressure-high temperature technique using a laser heated diamond anvil cell (LHDAC). The synthesis is carried out by laser heating a mixture of pure elements, Ru and C, at very low 'pressure' of 5 GPa and T ~ 2000 K. The structure of the temperature quenched high pressure phase is characterized by in situ high pressure x-ray diffraction (HPXRD) and is corroborated by ex situ TEM imaging and diffraction, carried out for the first time on the retrieved sample synthesized by LHDAC. The lattice parameters of Ru(2)C at ambient pressure are found to be a = 2.534 A and c = 4.147 A. In situ HPXRD studies up to 14.2 GPa yield a bulk modulus of 178(4) GPa. Electronic structure calculations reveal the system to be metallic in nature with a degree of covalence along the Ru-C bond. As ruthenium is isoelectronic to osmium, this result for Ru(2)C has significant implications in the synthesis and study of osmium carbides.

Some Evidence for the Formation of an Azo Bond during the Electroreduction of Diazonium Salts on Au Substrates

Abstract: Molecular films obtained by electrochemical reduction of diazoniuim tetrafluoroborate salts [4-carboxybenzene (PhCOOH) and 4-amino-(2,3,5,6-tetrafluoro)-carboxybenzene (PhF(4)COOH)] on Au substrates and post-functionalization with an osmium pyridil-bipyridine complex are studied by a combination of X-ray photoelectron (XPS) and polarization-modulation infrared reflection absorption spectroscopy (PM-IRRAS). The spectroscopic evidence suggests the formation of N=N bonds tethering the complexes to Au. The surface coverage of the azo-bonded osmium complexes strongly depends on the electrode potential. The resulting tethered osmium redox centres were characterized by cyclic voltammetry and impedance spectroscopy. Similar electron transfer-rate constants were measured for both fluorinated and non fluorinated benzene-linked Os complexes.

Superhard transition metal tetranitrides: XN 4 (X = Re, Os, W)

Abstract: The structural, mechanical, and electronic properties of rhenium, osmium, and tungsten tetranitrides, XN4 (X = Re, Os, W) with the orthorhombic ReP4-type structure have been investigated by first-principles calculations using density functional plane-wave pseudopotential method. The calculated formation enthalpies and elastic constants show that these tetranitrides are energetically and mechanically stable. It is appeared from the calculated band structures and density of states that ReN4 and new proposed WN4 are metallic, while OsN4 is semiconductor with a band gap of 0.64 eV. The hardness values of all compounds obtained from different hardness methods indicate that these tetranitrides are superhard materials.

Atomically Resolved Site-Isolated Catalyst on MgO: Mononuclear Osmium Dicarbonyls formed from Os3(CO)12

Abstract: Supported triosmium clusters, formed from Os3(CO)12 on MgO, were treated in helium at 548 K for 2 h, causing fragmentation of the cluster frame and the formation of mononuclear osmium dicarbonyls. The cluster breakup and the resultant fragmented species were characterized by infrared and X-ray absorption spectroscopies, and the fragmented species were imaged by scanning transmission electron microscopy. The spectra identify the surface osmium complexes as Os(CO)2{Osupport}n (n = 3 or 4) (where the braces denote support surface atoms). The images show site-isolated Os atoms in mononuclear osmium species on MgO. The intensity analysis on the images of the MgO(110) face showed that the Os atoms were located atop Mg columns. This information led to a model of the Os(CO)2 on MgO(110), with the distances approximated as those determined by EXAFS spectroscopy, which are an average over the whole MgO surface; the results imply that these complexes were located at Mg vacancies.

Alloy-comprising catalyst, method of preparation and uses

Abstract: A method of making a supported catalytic species comprising an alloy of at least two metals, comprisesthe steps of: (i)combining a particulate support material, a solution of a first metal compound, a solution of a secondmetal compound, and a solution of an alkaline precipitating agent to form a slurry mixture; (ii)agitating the resultant mixture; and (iii)contacting the solids with a reducing agent, wherein the first metal in the first metal compound and the second metal in the second metal compound is each independently selected from the group consisting of gold, palladium, platinum, rhodium, iridium, silver, osmium and ruthenium; and wherein the first metal is not the same as the second metal. [No Figure]

High-pressure behavior of osmium: An analog for iron in Earth’s core

Abstract: High-resolution x-ray diffraction with diamond-anvil cells, using argon as a quasi-hydrostatic pressure medium, documents the crystal structure and equation of state of osmium to over 60 GPa at room temperature. We find the zero-pressure bulk modulus in fair agreement with other experiments as well as with relativistic electronic band-structure calculations: Osmium is the densest but not the most incompressible element at ambient conditions. We also find no evidence for anomalies in the ratio of unit-cell parameters, c/a, or in the compressibility of osmium as a function of pressure. This is in agreement with other experiments and quantum mechanical calculations but disagrees with recent claims that the electronic structure and equation of state of osmium exhibit anomalies at pressures of ∼15-25 GPa; the discrepancies are may be due to the effects of texturing.

Spirobifluorene bridged Ir(III) and Os(II) polypyridyl arrays: synthesis, photophysical characterization, and energy transfer dynamics.

Abstract: The synthesis, characterization, photophysics, and time-dependent density functional theory (TD-DFT) calculations of spirobifluorene-bipyridine based iridium(III), osmium(II), and mixed Ir/Os complexes are presented. The preparation of the reference and mixed complexes proceeded step-by-step and microwave irradiation facilitated the complexation of osmium. The absorption of the target heterobimetallic derivative, Ir-L-Os, is described by linear combination of half of the absorption spectra of the homobimetallic analogues, Ir-L-Ir and Os-L-Os, due to the occurrence of mixed ligand and metal based transitions when the spirobifluorene-(bpy)2 bridging ligand L is linked to the metal, confirming a negligible interaction between the substituted metallic chromophores. TD-DFT calculations on monometallic, homo- and hetero-bimetallic complexes fully disentangled the origin of the absorption features. Noticeably, in the mixed Ir-L-Os complex an almost quantitative energy transfer from the 3Ir to the 3Os MLCT state ...

Chemiluminescence from osmium(II) complexes with phenanthroline, diphosphine and diarsine ligands

Abstract: The reaction of various [Os(L)2(L′)]2+ complexes (where L and L′ are phenanthroline, diphosphine or diarsine ligands) and organic reducing agents after chemical or electrochemical oxidation of the reactants produces an emission of light corresponding to MLCT transitions. In certain instances, the emission was greater than that of [Ru(bipy)3]2+, but the relative signals were dependent on many factors, including reagent concentration, mode of oxidation, reducing agent and the sensitivity of the photodetector over the wavelength range.

Ferromagnetic elements by epitaxial growth: A density functional prediction

Abstract: The periodic table contains only six natural elements with a ferromagnetic ground state. For example, the metal uranium, which is magnetically ordered in many compounds, is paramagnetic in all its known elemental bulk phases. Also, the iron-group elements ruthenium and osmium are known to be bulk paramagnets. We predict by means of density functional calculations that epitaxial growth of uranium, ruthenium, or osmium on suitable substrates may allow stabilization of bulklike films with tetragonal structures showing ferromagnetic order.

A Density Functional Theory Study on Carbon Monoxide Adsorption on Platinum–Osmium and Platinum–Ruthenium–Osmium Alloys

Abstract: Periodic density functional theory calculations on carbon monoxide (CO) adsorbed atop on platinum–osmium binary alloys (PtOs2 and PtOs4) and the platinum–ruthenium–osmium tertiary alloy (PtRu2Os2) are used to elucidate the changes in the C–O and C–Pt bonds upon alloying Pt with Ru/Os atoms. As Pt is alloyed with Ru/Os atoms, the adsorbate internal bond (C–O bond) and the adsorbate–metal bond (C–Pt bond) strengthen following the substrate trends of PtOs4 > Pt > PtOs2 > PtRu2Os2 and Pt > PtOs4 > PtOs2 > PtRu2Os2, respectively. These trends are manifested by the corresponding C–O and C–Pt stretching frequencies and the CO adsorption energy variations. Here, we establish a theoretical framework based on the π-attraction σ-repulsion mechanism to explain the above results. This model correlates the charges, polarizations, and electron densities of the adsorbate CO orbitals, and the sp/d populations of the adsorbing Pt atom. For the systems studied here, the traditional theoretical model of 5σ-donation/2π*-back-...

Oxidation of Phenol by Tris(1,10-phenanthroline)osmium(III)

Abstract: Outer-sphere oxidation of phenols is under intense scrutiny because of questions related to the dynamics of proton-coupled electron transfer (PCET). Oxidation by cationic transition-metal complexes in aqueous solution presents special challenges because of the potential participation of the solvent as a proton acceptor and of the buffers as general base catalysts. Here we report that oxidation of phenol by a deficiency of [Os(phen)3]3+, as determined by stopped-flow spectrophotometry, yields a unique rate law that is second order in [osmium(III)] and [phenol] and inverse second order in [osmium(II)] and [H+]. A mechanism is inferred in which the phenoxyl radical is produced through a rapid PCET preequilibrium, followed by rate-limiting phenoxyl radical coupling. Marcus theory predicts that the rate of electron transfer from phenoxide to osmium(III) is fast enough to account for the rapid PCET preequilibrium, but it does not rule out the intervention of other pathways such as concerted proton–electron tran...

Gel Having Improved Thermal Stability

Abstract: A gel has improved thermal stability and is the ultraviolet hydrosilylation reaction product of (A) an organopolysiloxane having an average of at least 01 silicon-bonded alkenyl group per molecule and (B) a cross-linker having an average of at least 2 silicon-bonded hydrogen atoms per molecule (A) and (B) react via hydrosilylation in the presence of (C) a UV-activated hydrosilylation catalyst comprising at least one of platinum, rhodium, ruthenium, palladium, osmium, and iridium, and (D) a thermal stabilizer The (D) thermal stabilizer is present in an amount of from about 001 to about 30 weight percent based on a total weight of (A) and (B) and having transparency to UV light sufficient for the ultraviolet hydrosilylation reaction product to form