Osmium Atoms Research Articles

A balance of redox and ligand-exchange processes in the reaction of H2[OsCl6] with thiourea: Isolation and characterization of a novel osmium complex [(NH2)2CSSC(NH2)2]2[OsIVCl6]Cl2·3H2O

A novel complex with the stoichiometry [(NH2)2CSSC(NH2)2]2[OsIVCl6]Cl2·3H2O (1) is isolated as a product of the reaction of H2[OsCl6] with thiourea in concentrated HCl under deliberately optimized conditions favoring a partial thiourea oxidation to α,α′-dithiobisformamidinium dication but preserving hexachloroosmate [OsCl6]2- anions. A bromide analogue [(NH2)2CSSC(NH2)2]2[OsIVBr6]Br2·3H2O 2 is afforded by a similar reaction. A counter synthesis of 1 is accomplished via the direct ion-exchange reaction between H2[OsCl6] and [S2C2(NH2)4]Cl2. Crystal structures of 1 and 2 are unambiguously established by synchrotron radiation-based single-crystal X-ray diffraction at 100 K. The two compounds are isostructural and are crystallized in the orthorhombic space group Cmcm, Z = 4. Unit cell parameters are for 1:a = 11.279(2) Å, b = 13.611(3) Å, c = 16.731(3) Å; for 2: a = 11.695(2) Å, b = 14.005(3) Å, c = 17.015(3) Å. The osmium atoms in [OsX6]2− (X = Cl or Br) anions adopt slightly distorted octahedral coordination. The α,α′-dithiobisformamidinium cations are paired into rings via the NH…Cl− hydrogen bonds. The rings are further linked into a spatial network by H-bonds with water molecules and S…Cl nonvalence interactions.

To Be Bridgehead or Not to Be? This is a Question of Metallabicycles on the Interplay between Aromaticity and Ring Strain

Transition-metal-containing metallaaromatics have attracted considerable interest from both experimental and computational chemists because they can display properties of both organometallic compounds and aromatic organic compounds. In general, the transition metal in a metallabicycle prefers a nonbridged position to the bridgehead one because of the larger ring strain caused by the rigidity in the bridgehead position, as exemplified by metallanaphthalene and metallanaphthalyne. On the contrary, the osmium atoms in recently synthesized osmapentalyne and osmapentalene are located at the bridgehead position. To probe the origin of the difference between these metallabicycles, we carried out density functional theory calculations. The metal-bridgehead osmanaphthalene and osmanaphthalyne are computed to be less stable by 17.9 and 26.3 kcal mol–1 than the non-metal-bridged ones, respectively. In addition, the metal-bridgehead osmapentalene and osmapentalyne are more stable by 11.8 and 22.8 kcal mol–1 than the ...

Ionization cross section, pressure shift and isotope shift measurements of osmium

In-gas-cell laser resonance ionization spectroscopy of neutral osmium atoms was performed with the use of a two-color two-step laser resonance ionization technique. Saturation curves for the ionization scheme were measured, and the ionization cross section was experimentally determined by solving the rate equations for the ground, intermediate and ionization continuum populations. The pressure shift and pressure broadening in the resonance spectra of the excitation transition were measured. The electronic factor for the transition nm to the intermediate state was deduced from the measured isotope shifts of stable Os isotopes. The efficient ionization scheme, pressure shift, nuclear isotope shift and are expected to be useful for applications of laser ion sources to unstable nuclei and for nuclear spectroscopy based on laser ionization techniques.

Clustering of transmutation elements tantalum, rhenium and osmium in tungsten in a fusion environment

The formation of transmutation solute-rich precipitates has been reported to seriously degrade the mechanical properties of tungsten in a fusion environment. However, the underlying mechanisms controlling the formation of the precipitates are still unknown. In this study, first-principles calculations are therefore performed to systemically determine the stable structures and binding energies of solute clusters in tungsten consisting of tantalum, rhenium and osmium atoms as well as irradiation-induced vacancies. These clusters are known to act as precursors for the formation of precipitates. We find that osmium can easily segregate to form clusters even in defect-free tungsten alloys, whereas extremely high tantalum and rhenium concentrations are required for the formation of clusters. Vacancies greatly facilitate the clustering of rhenium and osmium, while tantalum is an exception. The binding energies of vacancy–osmium clusters are found to be much higher than those of vacancy–tantalum and vacancy–rhenium clusters. Osmium is observed to strongly promote the formation of vacancy–rhenium clusters, while tantalum can suppress the formation of vacancy–rhenium and vacancy–osmium clusters. The local strain and electronic structure are analyzed to reveal the underlying mechanisms governing the cluster formation. Employing the law of mass action, we predict the evolution of the relative concentration of vacancy–rhenium clusters. This work presents a microscopic picture describing the nucleation and growth of solute clusters in tungsten alloys in a fusion reactor environment, and thereby explains recent experimental phenomena.

Monolayer of the 5d transition metal trichloride OsCl3 : A playground for two-dimensional magnetism, room-temperature quantum anomalous Hall effect, and topological phase transitions

Based on density functional theory (DFT) calculations, we predict that a monolayer of OsCl$_3$---a layered material whose interlayer coupling is weaker than in graphite---possesses a quantum anomalous Hall (QAH) insulating phase generated by the combination of honeycomb lattice of osmium atoms, their strong spin-orbit coupling (SOC) and ferromagnetic ground state with {\em in-plane} easy-axis. The band gap opened by SOC is \mbox{$E_g \simeq 67$ meV} (or \mbox{$\simeq 191$ meV} if the easy-axis can be tilted out of the plane by an external electric field), and the estimated Curie temperature of such {\em anisotropic planar rotator} ferromagnet is $T_\mathrm{C} \lesssim 350$ K. The Chern number $\mathcal{C}=-1$, generated by the manifold of Os $t_{2g}$ bands crossing the Fermi energy, signifies the presence of a single chiral edge state in nanoribbons of finite width, where we further show that edge states are spatially narrower for zigzag than armchair edges and investigate edge-state transport in the presence of vacancies at Os sites. Since $5d$ electrons of Os exhibit {\em both} strong SOC and moderate correlation effects, we employ DFT+U calculations to show how increasing on-site Coulomb repulsion $U$: gradually reduces $E_g$ while maintaining $\mathcal{C} = -1$ for $0 < U < U_c$; leads to metallic phase with $E_g = 0$ at $U_c$; and opens the gap of topologically trivial Mott insulating phase with $\mathcal{C}=0$ for $U > U_c$.

NbOsSi and TaOsSi – Two new superconducting ternary osmium silicides

The new equiatomic silicides NbOsSi and TaOsSi as well as ZrOsSi, TIrSi (T = Zr, Hf, Nb, Ta) and TPtSi (T = Nb, Ta) were prepared from the elements by arc-melting. These silicides crystallize with the orthorhombic TiNiSi type structure, space group Pnma. Irregularly shaped crystals of ZrOsSi, NbOsSi, TaOsSi, ZrIrSi and HfIrSi were separated from the annealed samples and investigated by single-crystal X-ray diffraction (a = 640.46(7), b = 404.07(5), c = 743.66(8) pm, wR2 = 0.0285, 390 F2 values, 20 variables for ZrOsSi; a = 629.78(6), b = 388.72(4), c = 727.48(7) pm, wR2 = 0.0350, 397 F2 values, 20 variables for NbOsSi, a = 626.80(6), b = 389.36(4), c = 726.22(7) pm, wR2 = 0.0501, 385 F2 values, 20 variables for TaOsSi, a = 653.48(8), b = 395.35(4), c = 739.19(8) pm, wR2 = 0.0427, 413 F2 values, 20 variables for ZrIrSi and a = 646.34(12), b = 393.57(7), c = 736.8(14) pm, wR2 = 0.0582, 371 F2 values, 20 variables for HfIrSi). The striking structural motifs in the new osmium compounds are three-dimensional [OsSi] networks (Os–Si: 240–251 pm) in which the osmium atoms have strongly distorted tetrahedral silicon coordination. High-pressure/high-temperature experiments (9.5 GPa/1520 K) on TaOsSi gave no hint for a structural phase transition. Temperature dependent measurements of the magnetic susceptibility and the electrical conductivity of NbOsSi and TaOsSi showed superconductivity below TC = 3.5 and 5.5 K, respectively. 29Si solid state MAS NMR investigations of the prepared silicides approved the structural models and showed a correlation between the observed 29Si resonance shifts and the electronegativity of the involved refractory metal.

The reaction of Os3(CO)12 with triphos {MeC(CH2PPh2)3}: A case of multiple C-P and C-H bond activations

The reaction of Os3(CO)12 with the tripodal ligand 1,1,1-tris(diphenylphosphinomethyl)ethane, triphos, results in the formation of the 48e trinuclear cluster complex Os3[μ-Ph2PCH2C(Me)(CH2PPh)CH2PC6H4](CO)7(η1-Ph). This new complex has been characterized by X-ray crystallography as well as by IR and NMR spectroscopy. The activation of the triphos ligand to yield the novel 9e donor ligand Ph2PCH2C(Me)(CH2PPh)CH2PC6H4 is unprecedented. The triphos ligand does not cap the triangular Os3 face; instead, the three phosphorus atoms are coordinated to only two of the metal atoms with the remaining osmium atom coordinated by an ortho-metalated aryl group. The triphos ligand is also transformed in several ways. Two C–P bonds are cleaved during the reaction, yielding an η1 phenyl ligand in the product and free benzene. The bonding in 1 has been examined by electronic structure calculations.

Current status of GALS setup in JINR

This is a brief report on the current status of the new GAs cell based Laser ionization Setup (GALS) at the Flerov Laboratory for Nuclear Reactions (FLNR) of the Joint Institute for Nuclear Research (JINR) in Dubna. GALS will exploit available beams from the U-400M cyclotron in low energy multi-nucleon transfer reactions to study exotic neutron-rich nuclei located in the “north-east” region of nuclear map. Products from 4.5 to 9 MeV/nucleon heavy-ion collisions, such as 136Xe on 208Pb, are thermalized and neutralized in a high pressure gas cell and subsequently selectively laser re-ionized. In order to choose the best scheme of ion extraction the results of computer simulations of two different systems are presented. The first off- and online experiment will be performed on osmium atoms that is regarded as a most convenient element for producing isotopes with neutron number in the vicinity of the magic N = 126.

Reactions of the face-capped benzothiazolate-substituted clusters Os3(CO)9(μ3,η2-C7H3NSR)(μ-H) (R = H, Me) with PPh3: Kinetic formation of Os3(CO)9(PPh3)(μ,η2-C7H3NSR)(μ-H) and thermally induced ligand isomerization

The reaction of the benzothiazolate-capped triosmium clusters Os3(CO)9(μ3,η2-C7H3NSR)(μ-H) (1a, R = H; 1b, R = Me) with PPh3 proceeds readily at room temperature with a μ3,η2 → μ,η2 hapticity change in the benzothiazolate heterocycle to furnish Os3(CO)9(PPh3)(μ,η2-C7H3NSR)(μ-H) (2a, R = H; 2b, R = Me) in high yields. X-ray crystallography has confirmed the regiospecific nature of this reaction where the PPh3 ligand is bound to the osmium atom that serves as the coordination site for the hydride and the metalated-carbon atom associated with the edge-bridged benzothiazolate ligand. The thermolysis of 2a and 2b in boiling toluene affords several new Os3 clusters as a result of ligand isomerization, decarbonylation, and ortho metalation of the ancillary PPh3 ligand. The new products have been isolated and characterized by a combination of spectroscopic methods and X-ray crystallography in the case of 3b, 4b, 5b and 6b. Clusters 3b and 4b are isomers of 2b and differ in the location of the hydride and PPh3 ligands relative to the benzothiazolate moiety. Electronic structure calculations on the isomeric clusters 2b, 3b, and 4b confirm that 2b is the kinetic product of ligand substitution, accounting for its rearrangement to the latter two isomers upon heating. Cluster 5b contains a face-capping benzothiazolate moiety and is shown by DFT calculations to derive from a site-selective loss of an axial CO group in 4b. Cluster 6a,b formed from 5a,b as a result of further decarbonylation with concomitant ortho metalation of one of the phenyl groups of the coordinated PPh3 ligand.

Electronic correlations in the ferroelectric metallic state ofLiOsO3

LiOsO$_3$ has been recently identified as the first unambiguous "ferroelectric metal", experimentally realizing a prediction from 1965 by Anderson and Blount. In this work, we investigate the metallic state in LiOsO$_3$ by means of infrared spectroscopy supplemented by Density Functional Theory and Dynamical Mean Field Theory calculations. Our measurements and theoretical calculations clearly show that LiOsO$_3$ is a very bad metal with a small quasiparticle weight, close to a Mott-Hubbard localization transition. The agreement between experiments and theory allows us to ascribe all the relevant features in the optical conductivity to strong electron-electron correlations within the $t_{2g}$ manifold of the osmium atoms.

Reactivity of 1.4-benzoquinone with trinuclear ruthenium and osmium clusters: Facile hydrogenation of the quinoid fragment

The reaction of [H2Os3(CO)10] with 1,4-benzoquinone yields initially a complex where the quinone bonds to the metal framework, both through a carbon atom of the ring and through an oxygen atom. Evidence suggests that this complex is a kinetic product which then transforms into complexes in which the quinone bonds through the oxygen atom. In one case, an oxygen atom of a hydroquinone moiety, bridges one of the metal–metal bonds, and in the other, a benzoquinone group acts, coordinated through the oxygen atoms, as a bridge between two trinuclear fragments. Similar products are obtained from the reaction of [Ru3(CO)12] with the same quinone in a hydrogen atmosphere although the presence of hydrogen leads to a partial hydrogenation of the benzoquinone ring. The reaction of [Os3(CO)10(MeCN)2] with the same quinone, formed a compound where the quinone is coordinate η2 through one of the double bonds of the ring to one of the osmium atoms. The products were characterized spectroscopically and; for four of the compounds; by X-ray crystallography.

Fluxional behaviour of phosphole and phosphine ligands on triosmium clusters

The unsaturated cluster [Os3(μ-H)2(CO)10] reacts with a variety of π-conjugated phosphole ligands: 2,5-bis(2-thienyl)-1-phenylphosphole, 2,5-bis(2-pyridyl)-1-phenylphosphole, and 1,2,5-triphenylphosphole, to give the monosubstituted [Os3(μ-H)(H)(CO)10(P)] and [Os3(μ-H)2(CO)9(P)] derivatives. Variable-temperature 1H NMR studies for the decacarbonyltriosmium complexes show that the hydride ligands undergo fluxional behavior and its decarbonylation gave the nonacarbonyl unsaturated species with equivalent hydrides. An X-ray crystallographic analysis of [Os3(μ-H)2(CO)9(P)] (2b) (P = 1,2,5-triphenylphosphole) is reported. From 2,5-bis(2-pyridyl)-1-phenylphosphole four isomers are obtained, the 1H NMR spectrum at low temperature indicates that the phosphole ligand may occupy pseudoaxial and equatorial sites at one of the osmium atoms bearing the bridging hydride. The reaction of [Os3(CO)10(CH3CN)2] with cyanoethyldiphenylphosphine affords mono- and bis(phosphine)-substituted clusters. The X-ray crystal structure of the monosubstituted [Os3(CO)11(η1-PC15H14N)] (3) derivative is discussed. The dynamic behavior observed for [Os3(CO)10(η1-PC15H14N)2] (4) is studied by variable-temperature 1H and 31P{1H} NMR spectroscopy. The latter studies show a mixture of two geometric isomers, which are in dynamic equilibrium at room temperature where the 1,2-trans–trans isomer (4a) is favored, whose molecular structure has been determined by X-ray crystallography.

High nuclearity clusters containing methyl groups. Synthesis and structures of pentaosmium-gold carbonyl cluster compounds

The compounds Os5(CO)15(μ3-AuPPh3)2, 2 and Os5(CO)14[μ4-Au3(PPh3)3](μ3-AuPPh3), 3 were obtained from the reaction of [PPN]2[Os5(CO)15] using [Au(PPh3)][NO3]. Compound 2 contains two triply-bridging Au(PPh3) groups. Compound 3 contains one triply-bridging Au(PPh3) group and a quadruply-bridging Au3(PPh3)3 group. When the same reaction was performed in the presence of CH3Au(PPh3), the new trigold compound Os5(CO)14(CH3)(μ3-AuPPh3)3, 4 was obtained. Compound 4 contains three triply-bridging Au(PPh3) groups and one methyl group coordinated to one of the apical osmium atoms of the trigonal bipyramidal pentaosmium cluster. Compound 4 was not obtained by the direct reaction of 2 with CH3Au(PPh3) but it was obtained when [Au(PPh3)][NO3] was added to the reaction solutions. Cationic digold species such as [CH3Au2(PPh3)2]+ have been proposed as a possible mechanism for the activation of CH3Au(PPh3) by [Au(PPh3)][NO3]. Compound 4 was also obtained albeit in a lower yield from the reaction of Os6(CO)18 with MeAu(PPh3) following treatment with Me3NO. Each of the pentaosmium products was characterized structurally by a single-crystal X-ray diffraction analysis.

Osmium Atoms and Os2 Molecules Move Faster on Selenium-Doped Compared to Sulfur-Doped Boronic Graphenic Surfaces.

We deposited Os atoms on S- and Se-doped boronic graphenic surfaces by electron bombardment of micelles containing 16e complexes [Os(p-cymene)(1,2-dicarba-closo-dodecarborane-1,2-diselenate/dithiolate)] encapsulated in a triblock copolymer. The surfaces were characterized by energy-dispersive X-ray (EDX) analysis and electron energy loss spectroscopy of energy filtered TEM (EFTEM). Os atoms moved ca. 26× faster on the B/Se surface compared to the B/S surface (233 ± 34 pm·s–1versus 8.9 ± 1.9 pm·s–1). Os atoms formed dimers with an average Os–Os distance of 0.284 ± 0.077 nm on the B/Se surface and 0.243 ± 0.059 nm on B/S, close to that in metallic Os. The Os2 molecules moved 0.83× and 0.65× more slowly than single Os atoms on B/S and B/Se surfaces, respectively, and again markedly faster (ca. 20×) on the B/Se surface (151 ± 45 pm·s–1 versus 7.4 ± 2.8 pm·s–1). Os atom motion did not follow Brownian motion and appears to involve anchoring sites, probably S and Se atoms. The ability to control the atomic motion of metal atoms and molecules on surfaces has potential for exploitation in nanodevices of the future.

Interactions between osmium atoms dissolved in iron observed by the 57Fe Mössbauer spectroscopy

Abstract The room temperature 57Fe Mössbauer spectra for binary iron-based solid solutions Fe1−x Os x , with x in the range 0.01 ≤ x ≤ 0.05, were analyzed in terms of binding energy E b between two Os atoms in the Fe-Os system. The extrapolated values of E b for x = 0 were used for computation of enthalpy of solution of osmium in iron. The result was compared with that resulting from the cellular atomic model of alloys by Miedema. The comparison shows that our findings are in qualitative agreement with the Miedema's model predictions.

Phenazine-substituted polynuclear osmium clusters: Synthesis and DFT evaluation of the C-metalated derivatives Os3(CO)9(μ3,η2-C12H7N2)(μ-H) and Os3(CO)9(μ3,η2-C12H6N2)(μ-H)2

Os3(CO)12 reacts with phenazine in refluxing xylene to yield the monohydride cluster Os3(CO)9(μ3,η2-C12H7N2)(μ-H) (1) in 18% yield and the dihydride cluster Os3(CO)9(μ3,η2-C12H6N2)(μ-H)2 (2) in 21% yield. Compound 1 reacts reversibly with CO to give the decacarbonyl compound Os3(CO)10(μ,η2-C12H7N2)(μ-H) (3) and with PPh3 to afford the addition product Os3(CO)9(μ,η2-C12H7N2)(PPh3)(μ-H) (4). Compounds 1, 2, and 4 have been structurally characterized. 1 contains a C-metalated phenazine ligand that is coordinated to the cluster by a dative nitrogen bond and a benzylidene-type bond, the latter which bridges the same cluster edge as the bridging hydride. The activated phenazine ligand in 2 derives from a double C–H bond metalation sequence, affording a face-capping heterocyclic ligand that binds adjacent osmium centers through two σ–Os–C bonds and the third osmium atom via an aryl π bond in an η2 fashion. Compound 4 exhibits a closed trimetallic Os3(CO)9 core that contains edge-bridging phenazine (C,N coordination) and hydride moieties, and a triphenylphosphine ligand that is coordinated at the non-phenazine-ligated osmium center. These compounds represent rare examples of polynuclear osmium clusters containing C-metalated phenazine ligands. The potential energy surfaces that afford clusters 1 and 2 from Os3(CO)12 and phenazine have been modeled by DFT calculations, and these data indicate that both product clusters originate from the unsaturated cluster Os3(CO)11.

Fused metallaborane clusters of group 9 and 8 transition metals

Building on our earlier results, the condensation of rhodium polychlorides with borane reagents (LiBH4·thf, BH3·thf, BHCl2·SMe2 etc.), we continue to explore the chemistry of the same system with metal carbonyl compounds. As a result, the reaction of [(Cp*Rh)2B2H6], generated from fast metathesis of [Cp*RhCl2]2 and LiBH4, with heavier group 8 metal carbonyl compounds, yielded [(Cp*Rh)2B4H4Rh{Cp*RhB3H8}], 1, [(Cp*Rh)B3H7{Ru(CO)2}(Cp*RhCO)2], 2 [(Cp*Rh)2B3H3{Ru(CO)3}2], 3 and [(Cp*Rh)2{Os4(CO)12}(B)H], 4. Further, these reaction also generated two mixed-metal tetrahedral hydrido clusters [(Cp*Rh){Os(CO)3}3(μ-H)4], 5 and [(Cp*Rh)2{Os(CO)3}2(μ-CO) (μ-H)2], 6 as minor products. Compound 1 is an octahedra and a square pyramid fused cluster, whereas for 2 a square pyramid and a triangle are fused through a vertex. Both 1 and 2 follow Mingos's formalism for fused clusters. Cluster 4 is an interstitial boride composed of one boron, two rhodium and four osmium atoms. Based on its compositions, compound 4 is a rare example of heteronuclear borides. All the compounds have been characterized by IR, 1H, 11B, 13C NMR spectroscopy in solution and the solid state structures were established by crystallographic analysis of 1–5.

Stability and mobility of rhenium and osmium in tungsten: first principles study

We report a series of ab initio studies based upon density functional theory for the behavior of rhenium and osmium atoms in body-centered-cubic tungsten crystal. Contrary to the fast one-dimensional migration of self-interstitial atoms, interstitials of these solute elements in tungsten have three-dimensional motion because they form a mixed dumbbell having a low rotation energy barrier. The migration of these solute elements strongly influences the effects of radiation upon the materials, and our results suggest that the low rotation energy barrier leading to three-dimensional migration is a property that is key to the explanation of the radiation effects experimentally observed in tungsten-rhenium and tungsten-osmium alloys.

Fabrication of crystals from single metal atoms.

Metal nanocrystals offer new concepts for the design of nanodevices with a range of potential applications. Currently the formation of metal nanocrystals cannot be controlled at the level of individual atoms. Here we describe a new general method for the fabrication of multi-heteroatom-doped graphitic matrices decorated with very small, ångström-sized, three-dimensional (3D)-metal crystals of defined size. We irradiate boron-rich precious-metal-encapsulated self-spreading polymer micelles with electrons and produce, in real time, a doped graphitic support on which individual osmium atoms hop and migrate to form 3D-nanocrystals, as small as 15 Å in diameter, within 1 h. Crystal growth can be observed, quantified and controlled in real time. We also synthesize the first examples of mixed ruthenium–osmium 3D-nanocrystals. This technology not only allows the production of ångström-sized homo- and hetero-crystals, but also provides new experimental insight into the dynamics of nanocrystals and pathways for their assembly from single atoms.

Magnetic phase transitions and iron valence in the double perovskite Sr 2 FeOsO 6

The insulating and antiferromagnetic double perovskite Sr2FeOsO6 has been studied by 57Fe Mossbauer spectroscopy between 5 and 295 K. The iron atoms are essentially in the Fe3 + high spin \(( {t_{2\mathrm{g}}{^3} e_\mathrm{g}{^2} } )\) and thus the osmium atoms in the Os\(^{5+} ( {t_{2\mathrm{g}}{^3} } )\) state. Two magnetic phase transitions, which according to neutron diffraction studies occur below TN = 140 K and T2 = 67 K, give rise to magnetic hyperfine patterns, which differ considerably in the hyperfine fields and thus, in the corresponding ordered magnetic moments. The evolution of hyperfine field distributions, average values of the hyperfine fields, and magnetic moments with temperature suggests that the magnetic state formed below TN is strongly frustrated. The frustration is released by a magneto-structural transition which below T2 leads to a different spin sequence along the c-direction of the tetragonal crystal structure.