Os Atoms Research Articles

Structural stability and phase transition in OsC and RuC

The structural stability and phase transition of osmium and ruthenium carbides (OsC and RuC) were investigated by first principles. Nine structures were considered for each carbide. Zinc blende structure has the lowest energy among the considered structures at ambient conditions for both carbides. For OsC at elevated pressures, the most stable phase is zinc blende structure from 0 to 10 GPa, FeSi from 10 to 32 GPa. In these two structures, Os atom is fourfold coordinated. From 32 to 40 GPa, tungsten carbide (WC) and NiAs are energetically competitive with Os atom sixfold coordinated. NiAs becomes energetically the most stable structure above 40 GPa. For RuC, zinc blende structure is the most stable from 0 to 20 GPa. From 20 to 100 GPa, WC structure is the most stable.

Electronic structures and spectroscopic properties of promising highly efficient red phosphorescent Os(II)(LR)2(PH3)2 complexes: a theoretical exploration

The red phosphorescent osmium(II) complexes [Os(LR)2(PH3)2] (L = 2-pyridyltriazole (ptz): R = H (1a), CF3 (1b), t-Bu (1c)); L = 2-pyridylpyrazole (ppz): R = H (2a), CF3 (2b), t-Bu (2c)); L = 2-phenylpyridine (ppy): R = H (3a)) were explored using density functional theory (DFT) methods. The ground- and excited-state geometries of the complexes were optimized at the B3LYP/LANL2DZ and UB3LYP/LANL2DZ levels, respectively. The absorption and phosphorescence of the complexes in CH2Cl2 media were calculated based on the optimized ground- and excited-state geometries using time-dependent density functional theory method with the polarized continuum model. The optimized geometry structural parameters of the complexes in the ground state agree well with the corresponding experimental values. The lower-lying unoccupied molecular orbitals of the complexes are dominantly localized on the L ligand, while the higher-lying occupied ones are composed of Os(II) atom and L ligand. The low-lying metal-to-ligand and intraligand charge transfer (MLCT/ILCT) transitions and high-lying ILCT transitions are red-shifted with the increase in the π-donating ability of the L ligand and the π electron-donating ability of R substituent. The calculation revealed that the phosphorescence originated from 3MLCT/3ILCT excited state. However, the complex 3a displayed different types of MLCT/ILCT excited state compared with that of 1a–2c, and the different types of transition were also found in the absorption. In addition, we found that the phosphorescence quantum efficiency of Os(II) complexes is related to the metal composition in the high-energy occupied molecular orbitals, it will be helpful to designing highly efficient phosphorescent materials.

Hydrogen Atoms Location in Os3(μ-H)(CO)9(μ3, η2-C2H) from Accurate X-Ray Data at 100 K

The structure of the complex Os3(μ-H)(CO)9(μ3, η2-C2H) has been determined using X-ray data collected at low temperature (100 K); all hydrogen atoms have been located. The asymmetric unit is formed by two molecules joined through hydrogen bonds involving the hydrogen atoms of C2H moiety and the oxygen atoms of carbonyl groups. The complex crystallizes in the monoclinic space group P21/c with a = 12.94040(2), b = 15.4705(2), c = 16.0164(2) A, β = 106.0860(10)°, and V = 3,080.85(7) A3, Z = 8. A molecule is formed by a triangular Os3 cluster, with metal atoms bearing terminal CO groups. The acetylenic residual is formally π-bonded to two Os atoms in a perpendicular mode and σ-linked to the third Os atom. A bridging hydride atom completes the coordination. An high resolution X-ray analysis at 100 K has allowed the location of hydrogen atoms in the Os3(μ-H)(CO)9(μ3, η2-C2H) complex; C–H···O hydrogen bonds connect the molecules in the crystal.

Dichlorido(η4-cycloocta-1,5-diene)bis(triphenylphosphine)osmium(II)

The OsII atom in the title compound, [OsCl2(C8H12)(C18H15P)2], is located on a crystallographic twofold axis and adopts a distorted octa­hedral coordination geometry. The two triphenyl­phosphine ligands are trans to each other, while the two chlorine ligands are cis-disposed. The coordination is completed by the cyclo­octa­diene (COD) ligand with bonding to the two olefin double bonds. The C=C bond has a length of 1.403 (6) Å, which is significntly longer than a free olefinic double bond (≃1.34 Å).

Infrared Spectra and Density Functional Theory Calculations of Group 8 Transition Metal Sulfide Molecules

Small sulfur molecules were reacted with laser-ablated Fe, Ru, and Os atoms in excess argon and condensed at 7 K. Reaction products were identified from matrix infrared spectra through sulfur-34 isotopic shifts, spectra of sulfur isotopic mixtures, and frequencies from density functional calculations. The strongest absorptions of the MS(2) disulfide molecules are observed at 540.2, 535.5, and 537.5 cm(-1), respectively, for the group 8 metals, and a 523.2 cm(-1) band is assigned to the FeS vibrational fundamental in solid argon. The FeS(2)(-) anion was detected in the spectrum at 542.1 cm(-1). The RuS(2) absorption exhibited resolved natural ruthenium isotopic splittings. Evidence is also presented for side-bound M(S(2)) isomers and MS(4) molecules with different structures including Fe(S(2))(2), (S(2))RuS(2), and tetrahedral OsS(4). Although OsO(4) is a well-known molecule, this, we believe, is the first experimental observation of OsS(4).

Formation of carbyne complexes in reactions of laser-ablated Os atoms with halomethanes: characterization by C–H(X) and Os–H(X) stretching absorptions and computed structures

Reactions of laser-ablated Os atoms with halomethanes have been investigated. Small carbyne complexes are produced in reactions of Os atoms with fluoromethanes and identified through matrix infrared spectra and vibrational frequencies computed by density functional theory. The preference for the carbon-osmium triple bond is traced to the low energy of the Os carbyne products. The C-H and C-X stretching absorptions of the carbyne complexes are observed on the high frequency sides of the corresponding precursor bands, which result from the high s character in the C-H bond and interaction between the C-X and C-Os stretching modes, respectively. The calculated Os complex structures show a large variation with the ligands and electronic states, similar to the analogous Ru complex structures. The present report also compares previous Fe, Ru, and Os results and supports the general trend that the higher oxidation state complexes become more stable on going down the family group column.

Theoretical studies on electronic structures and spectroscopic properties of a series of novel β-diketonate Os(II) complexes

The geometries, electronic structures, and spectroscopic properties of a series of [Os(II)(CO)3(tfa)(acac(X)2)] (tfa = trifluoroacetate; acac = acetoylacetonate; X = H (1), CF3 (2), C6H5 (3), and C10H7 (4)) complexes have been investigated theoretically. The ground and excited state geometries were optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ levels, respectively. The optimized geometry structural parameters agreed well with the corresponding experimental results. As indicated in this paper, the highest occupied molecular orbitals were dominantly localized on the Os atom, ctfa (abbv. of CO and tfa), and acac ligand for 1 and 2, acac ligand and X substituent for 3 and 4, while the lowest unoccupied molecular orbitals were mainly composed of acac ligand and X substituent. Under the time-dependent density functional theory (TDDFT) level with the polarized continuum model (PCM), the absorption and phosphorescence in CH2Cl2 media were calculated based on the optimized ground- and excited-state geometries, respectively. The calculated results show that the lowest energy absorptions at 317 (1), 342 (2), 377 (3), and 420 nm (4) are attributed to a change of ππ*/MLCT mixing transition to pure ππ* transition for 1–4, while their phosphorescence emission have similar transition properties. This indicates that the absorption and emission transition characters could be altered by adjusting the π electron-donating ability.

X-ray and conformation analysis of the new trinuclear cluster of osmium Os3(μ,η2-OCC6H5)(η3-C3H5)(CO)9

The crystal structure of the Os3(μ,η2-O=CC6H5)(η3-C3H5)(CO)9 cluster synthesized by the reaction of the (μ-H)Os3(μ-O=CC6H5)(CO)10 complex with allylamine in chloroform was determined by X-ray analysis. Prolonged storage of the reaction mixture led to N-C bond cleavage in allylamine and η3-addition of the allyl fragment at one of the Os atoms (Os-C 2.246 A, 2.248 A, and 2.273 A). The unit cell parameters of the complex are a = 9.494(1) A, b = 10.479(1) A, c = 12.474(2) A, α = 84.55(1)°, β = 70.08(1)°, γ = 70.72(1)°, V = 1255.8(4), A3, space group P\( \bar 1 \), Z = 2; C19H10O10Os3; dcalc = 2.922 g/cm3, 3085 Ihkl > 2σI of 3611 collected reflections; R = 0.0252. The structure of Os3(μ,η2-O=CC6H5)(η3-C3H5)(CO)9 is molecular. The plane of the Os3 triangle and the OsCOOs plane are connected according to the “butterfly” principle with an angle of 103.4° between them. The Os-Os distances in the cluster core vary from 2.836(1) A to 2.844(1) A; the Os-Ccarb distances are 1.88(1)–1.97(1) A; the distances to the atoms of the bridging ligands are Os-C 2.11(1) A, Os-O 2.14(1) A; the O-C bridging bond is 1.24(1) A. of the Os3(μ,η2-O=CC6H5)(η3-C3H5)(CO)9 triosmium cluster were studied theoretically. The potential curve of the internal rotation of the allyl ligand relative to the Os(1)-C(9) bond was determined. The rotation barrier of the allyl ligand in crystal relative to the Os(1)-C(9) bond is 8.38 kJ/mol, and the rotation of the ligand is not hindered. The effects of the intra-and intermolecular interactions on the conformation state of the cluster complex are considered.

Decacarbonyl-1κ3C,2κ3C,3κ4C-μ-hydrido-1:2κ2H:H-(μ-quinoline-2-thiolato-1:2κ2S:S)diosmium(I)osmium(0)(3Os—Os)

The title compound, [Os3(C9H6NS)H(CO)10], contains a nearly equilateral triangle of Os atoms. Two of the Os atoms are bridged by an S atom of the quinoline-2-thiol­ate ligand. Ten carbonyl groups complete the cluster, resulting in a distorted octa­hedral geometry for each Os atom. The hydride atom, which was located in a difference Fourier map and refined isotropically, bridges the shortest Os–Os edge.

Methylidyne Complexes Prepared by Reactions of Laser-Ablated Os Atoms with Methane, Methyl Halides, and Ethane: Observation of the C—H and Os—H Stretching Absorptions

Simple Os carbyne complexes (HC≡OsH3, HC≡OsH2F, HC≡OsH2Cl, HC≡OsH2Br, and CH3C≡OsH3) are produced in reactions of laser-ablated Os atoms with small alkanes and methyl halides via oxidative C−H insertion and α-hydrogen migration. The diagnostic methylidyne C—H stretching absorptions of HC≡OsH3 and its halide derivatives are observed about 200 cm−1 above the precursor C—H stretching bands, and the frequencies are consistent with s character in hybridization in the C—H bond. The methylidyne complexes all have computed Cs structures, and particularly the HC≡OsH3 and CH3C≡OsH3 complexes have two equivalent shorter and one longer Os—H bonds, parallel to the case of Re in similar complexes. The strong unique Os—H stretching absorption at an exceptionally low frequency is traced to the stretching mode of the long Os—H bond and antibonding character in the doubly occupied HOMO.

Determination of quantitative distributions of heavy-metal stain in biological specimens by annular dark-field STEM

It is shown that dark-field images collected in the scanning transmission electron microscope (STEM) at two different camera lengths yield quantitative distributions of both the heavy and light atoms in a stained biological specimen. Quantitative analysis of the paired STEM images requires knowledge of the elastic scattering cross sections, which are calculated from the NIST elastic scattering cross section database. The results reveal quantitative information about the distribution of fixative and stain within the biological matrix, and provide a basis for assessing detection limits for heavy-metal clusters used to label intracellular proteins. In sectioned cells that have been stained only with osmium tetroxide, we find an average of 1.2+/-0.1 Os atom per nm(3), corresponding to an atomic ratio of Os:C atoms of approximately 0.02, which indicates that small heavy atom clusters of Undecagold and Nanogold can be detected in lightly stained specimens.

Two modes of C–H bond activation of tris(2-thienyl)phosphine in trinuclear osmium carbonyl clusters

Tris(2-thienyl)phosphine, P(C 4H 3S) 3, reacts with [Os 3(CO) 12] at 110 °C to give the phosphine-substituted derivatives [Os 3(CO) 11{P(C 4H 3S) 3}] ( 1), [Os 3(CO) 10{P(C 4H 3S) 3} 2] ( 2) and [Os 3(CO) 9{P(C 4H 3S) 3} 3] ( 4), as well as the C–H activated product [Os 3(μ-H)(CO) 9{μ-P(C 4H 2S)(C 4H 3S) 2}{P(C 4H 3S) 3}] ( 3), in which the bridging ligand is equatorially coordinated to two osmium atoms. Thermolysis of 2 in refluxing toluene results in the formation of 3. Compound 1 can also be prepared in high yield from [Os 3(CO) 11(NCMe)]. The reaction of [Os 3(μ-H) 2(CO) 10] with tris(2-thienyl)phosphine at room temperature afforded [Os 3(μ-H) 2(CO) 9{P(C 4H 3S) 3}] ( 5) and [Os 3H(μ-H)(CO) 10{P(C 4H 3S) 3}] ( 6), with the ligand coordinated through the phosphorus atom whereas at elevated temperature the cyclometallated compounds [Os 3(μ-H)(CO) 9{μ 3-P(C 4H 2S)(C 4H 3S) 2}] ( 7) and [Os 3(μ-H)(CO) 8{μ 3-P(C 4H 2S)(C 4H 3S) 2{P(C 4H 3S) 3}] ( 8) were obtained in addition to 5. Heating 6 in refluxing heptane furnished 5 via loss of one carbonyl ligand. Thermolysis of 1 and 3 in refluxing toluene gives 7 and 8, respectively, in good yields. In 3, the μ-P(C 4H 2S)(C 4H 3S) 2 ligand is coordinated through the phosphorus to one Os atom and through a σ–Os–C bond to the second osmium atom. Compound 7 contains the μ 3-P(C 4H 2S)(C 4H 3S) 2 ligand bound through phosphorus to one Os atom, through a σ–Os–C bond to another and by an η 2 (π)-interaction to the third osmium atom. Compounds 1, 2 and 4 contain the ligand coordinated exclusively through the phosphorus atom. The crystal and molecular structures of 2, 3, 5, 6 and 7 are reported.

Theory of enhanced magnetic anisotropy induced by Pt adatoms on two-dimensional Co clusters supported on a Pt(111) substrate

Calculations are reported of the magnetic anisotropy energy of two-dimensional (2D) Co nanostructures on a Pt(111) substrate. The perpendicular magnetic anisotropy (PMA) of the 2D Co clusters strongly depends on their size and shape, and rapidly decreases with increasing cluster size. The PMA calculated is in reasonable agreement with experimental results. The sensitivity of the results to the Co-Pt spacing at the interface is also investigated and, in particular, for a complete Co monolayer we note that the value of the spacing at the interface determines whether PMA or in-plane anisotropy occurs. We find that the PMA can be greatly enhanced by the addition of Pt adatoms to the top surface of the 2D Co clusters. A single Pt atom can induce in excess of $5\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ to the anisotropy energy of a cluster. In the absence of the Pt adatoms the PMA of the Co clusters falls below $1\phantom{\rule{0.3em}{0ex}}\mathrm{meV}∕\mathrm{Co}$ atom for clusters of about 10 atoms whereas, with Pt atoms added to the surface of the clusters, a PMA of $1\phantom{\rule{0.3em}{0ex}}\mathrm{meV}∕\mathrm{Co}$ atom can be maintained for clusters as large as about 40 atoms. The effect of placing Os atoms on the top of the Co clusters is also considered. The addition of $5d$ atoms and clusters on the top of ferromagnetic nanoparticles may provide an approach to tune the magnetic anisotropy and moment separately.

A New Tris(diphenylstannylene)triosmium Carbonyl Cluster Complex and Its Reactions with Pt(PBut3)2and Pt(PPh3)4

The reaction of Os3(CO)12 with Ph3SnH yielded the bimetallic Os−Sn cluster complexes Os3(CO)11(SnPh3)(μ-H) (16) and Os3(CO)9(μ-SnPh2)3 (17) in 20 and 21% yields, respectively. Compound 16 consists of an Os3 triangle with a terminal SnPh3 group on one of the Os atoms and a bridging hydrido ligand across one of the Os−Os bonds. Compound 17 consists of a central Os3 triangle with SnPh2 groups bridging each of the three Os−Os bonds. Pt(PBut3)2 reacts with compound 17 to afford Os3(CO)9[Pt(PBut3)](μ-SnPh2)3 (18), a Pt(PBut3) adduct of 17, in 29% yield by adding a Pt(PBut3) group across one of the Os−Sn bonds. The osmium and tin atoms lie in a plane, while the Pt(PBut3) group is displaced slightly out of that plane. Pt(PPh3)4 reacts with 17 to give the cluster complex Os3(CO)9[Pt(Ph)(PPh3)2](μ-SnPh2)2(μ3-SnPh) (19) in 21% yield by insertion of a Pt(PPh3)2 into one of the Sn−C bonds to one of the phenyl groups. The osmium and tin atoms are coplanar, and there is a Pt(Ph)(PPh3)2 group terminally bonded to one of ...

Trisodium dihydroxotetraoxoosmate(VII), Na3[OsO4(OH)2

Na3[OsO4(OH)2] contains osmium(VII) coordinated octa­hedrally by four oxide and two hydroxide groups. The OsO4(OH)2 octa­hedra form zigzag chains parallel to [010], linked by hydrogen bridges. Two O atoms, one Na and the Os atom lie on a mirror plane.

The series Os4(µx-η2-C2Ph2)(CO)14–n(n = 0, 1, 2;x = n+ 2) — Models for site-specific surface catalysts

The cluster Os4(µ-η2-C2Ph2)(CO)14(1) has been prepared from the reaction of Os4(CO)14and C2Ph2in CH2Cl2at 25 °C. Other minor products include the known clusters Os3(µ3-η2-C2Ph2)(CO)10and Os3(µ-η4-C4Ph4)(CO)9. The structure of 1 reveals an approximately planar C2Os4skeleton with a dimetallacyclobutene ring (C—C = 1.32(4) Å) and a flat butterfly Os4unit (Os—Os range = 2.859(2)–2.916(2) Å). The13C{1H} NMR spectrum of 1 indicates the carbonyl ligands are rigid at room temperature. Stirring 1 in CH2Cl2for 2 days (ambient temperature) afforded Os4(µ3-η2-C2Ph2)(CO)13(2). The Os atoms in 2 also have an almost flat butterfly arrangement (Os—Os range = 2.7392(7)–2.8947(6) Å) with the alkyne ligand located over one of the Os3triangles. The13C NMR data for 2 are consistent with rapid rotation on the NMR timescale of the hinge Os(CO)3units at 21 °C, but slow rotation at –50 °C. Heating 2 at 40 °C gave Os4(µ4-η2-C2Ph2)(CO)12(3) after 2 days. Cluster 3 has the common butterfly arrangement of Os atoms with the C2Ph2bound to all four metal atoms (Os—Os range = 2.7457(5)–2.8742(5) Å). The13C{1H} NMR spectra of 3 at 21 and 90 °C indicate there is rapid CO exchange of the carbonyls of the two types of Os(CO)3units, but not between the units. The spectrum at –90 °C indicates one of the rotations (presumed to be that involving the carbonyls of the wingtip Os(CO)3units) is slowed on the NMR timescale. Compounds 1–3 form a unique series of clusters that have an alkyne ligand bound to two, three, and four metal atoms. Compound 1 is a model for a corner, compound 2 for a planar surface, and compound 3 a step site, in site-specific surface catalysts.Key words: osmium cluster, diphenylacetylene, dimetallacyclobutene, carbonyl exchange, surface catalysis.

Decacarbonyl-1κ3C,2κ3C,3κ4C-(μ-pentafluorophenylhydrazine-1κN:2κN′)-triangulo-triosmium: a hydrazino-edge-bridged triangular triosmium cluster

The title compound, [Os3(C6F5NHNH2)(CO)10], contains a near regular triangle of Os atoms. Two of the metal atoms are bridged by the hydrazine group of the C6F5NHNH2 ligand. Ten carbonyl groups complete the cluster, resulting in a distorted octa­hedral coordination for each Os atom.

Helicobacter pylorieradication for the treatment of dyspeptic symptoms in chronic renal failure

From Clinical Hospital Split, *Department of Gastroenterology and Hepatology, †Department of Nephrology, ‡Department of Pathology, §Department of Microbiology, Split, CroatiaCorrespondence:Prof. Izet Hozo MD, PhDDepartment of Internal Medicine,Clinical Hospital Split, Soltanska 1, Split, CroatiaTel: 385-21-55-76-58Fax: 385-21-55-76-58Izet.Hozo@st.htnet.hrAccepted for publicationNovember 2004

Ferromagnetism of OsFe 3N

The iron nitride OsFe 3N is investigated from ab initio calculations of the electronic structure with the full potential-linearized augmented plane wave (FP-LAPW) method. The generalized gradient approximation is used for the treatment of the exchange-correlation energy. The N atom possess a larger moment in the Os-based system, in spite of the decrease of the overall magnetization with the Os substitution. The calculations indicate a large contribution from valence electrons to the magnetic hyperfine field of the Os atom, which arises from a strong polarization of the valence s-electrons and the formation of bonding states between the Fe and Os atoms. The same amount of mixing between the d-band and the conduction band is observed for the Fe atoms in both nitrides.

Nonacarbonyl-μ3-N,N-diethyldithiocarbamato-κ3S:S:S′-μ-hydrido-triosmium(3Os—Os)

The molecular structure of the title compound, [Os3(C5H10NS2)H(CO)9], consists of an Os3 triangle with a bridging dithio­carbamate ligand acting as a five-electron donor; a hydride ligand is located between two Os atoms. Three terminal carbonyl groups on each Os atom complete the structure. There are two independent mol­ecules in the asymmetric unit.