Syntheses and structures of Osmium(II) and Osmium(VI) <Emphasis Type="Italic">meso</Emphasis>-tetra(benzo-15-crown-5)porphyrinates according to the spectral data

The reaction of meso-tetra(benzo-15-crown-5)porphyrin (H₂TCP) with the osmium carbonyl complex Os₃(CO)₁₂ yieds the corresponding osmium(II) porphyrinate OsTCP(CO). The oxidation of OsTCP(CO) with air oxygen and hydrogen peroxide in neutral and acidic media was studied. A preparative method for the synthesis of osmium(VI) meso-tetra(benzo-15-crown-5)porphyrinate (OsO₂) TCP by the oxidation of OsTCP(CO) with 50% hydrogen peroxide in acetic acid was developed. The structures of new osmium porphyrinates were determined by IR, ¹H NMR, and UV/Vis spectroscopies.     

Study of the system Os(IV)-chloride-brilliant green: Extraction-spectrophotometric determination of osmium

A sensitive extraction-spectrophotometric method of the determination of osmium, taking advantage of the ion-associate of the chloride osmium anion with brilliant green has been developed. The complex is extracted from aqueous phase with a mixture of C₆H₅Cl + CCl₄ (3 + 1). Molar absorptivity () at 640 nm is 1.95 × 10⁵ liters mol⁻¹cm⁻¹ (specific ABSORPTIVITY = 1.03). The relative standard deviation is 1–3%. The mole ratio of Os:BG in the complex is 1:3. Platinum metals interfere with the determination of osmium. The determination can be highly selective after preliminary separation of osmium by distillation as OsO₄.     

A Terminal Osmium(IV) Nitride: Ammonia Formation and Ambiphilic Reactivity

Low‐valent osmium nitrides are discussed as intermediates in nitrogen fixation schemes. However, rational synthetic routes that lead to isolable examples are currently unknown. Here, the synthesis of the square‐planar osmium(IV) nitride [OsN(PNP)] (PNP=N(CH₂CH₂P(tBu)₂)₂) is reported upon reversible deprotonation of osmium(VI) hydride [Os(N)H(PNP)]⁺. The Os^IV complex shows ambiphilic nitride reactivity with SiMe₃Br and PMe₃, respectively. Importantly, the hydrogenolysis with H₂ gives ammonia and the polyhydride complex [OsH₄(HPNP)] in 80 % yield. Hence, our results directly demonstrate the role of low‐valent osmium nitrides and of heterolytic H₂ activation for ammonia synthesis with H₂ under basic conditions.     

Photometric determination of osmium with thiourea after extraction of the tetroxide

A general method for the determination of 5–1000 γ of osmium involves extraction of osmium tetroxide with chloroform or carbon tetrachloride, followed by shaking the organic solvent with a sulfuric acid solution, of thiourea to form red Os(NH₂CSNH₂)₆⁺³, whose color intensity is measured photometrically. A sharp separation of osmium from ruthenium can be obtained by reducing Os(VIII) and Ru(VIII) with ferrous sulfate and then oxidizing Os(IV) to Os(VIII) with nitric acid; ruthenium remains reduced and is not extracted by chloroform or carbon tetrachloride.     

Investigations of changes in the oxidation state of the catalyst during the OsO4-catalysed decomposition of hydrogen peroxide

By using different methods, such as spectrophotometry, potentiometric titration, polarography and extraction, it was found that at pH 8.5 osmium (VIII) is reduced by hydrogen peroxide to osmium(VI) to various extents. At pH 10.6, where the rate of the OsO₄-catalysed decomposition of hydrogen peroxide reaches its maximum, the concentration ratio of osmium (VIII) and osmium (VI) was found to be nearly one. This favours the explanation that the maximum rate of hydrogen peroxide decomposition is found at the pH where the rate of reduction of osmium (VIII) by hydrogen peroxide just becomes equal to the rate of oxidation of osmium (VI) by hydrogen peroxide.     

Complexes of osmium with tertiary arsines and carbonmonoxide

Osmium halides (Cl and Br) react with monotertiary arsines Ph₂RAs (R=Me, Et, Pr and Bu) in alcoholic medium to give paramagnetic octahedral complexes of the type OsX₃L₃ (X=Cl, Br; L=Ph₂RAs) which further react with carbonmonoxide to give dihalo dicarbonyl complexes of osmium(II) of the type OsX₂ (CO)₂ L₂. Similarly, osmium halides react with tertiary arsines in the presence of formaldehyde to give monocarbonyl complexes of osmium(II) of the type OsX₂ (CO)L₃. Structures have been assigned to all these compounds on the basis of IR and NMR studies.     

Chemistry of osmium in N2P2Br2 coordination sphere: Synthesis,structure and reactivities

A family of three mixed-ligand osmium complexes of type [Os(PPh₃)₂(N-N)Br₂], where N-N=2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (Me₂bpy) and 1,10-phenanthroline (phen), have been synthesized and characterized. The complexes are diamagnetic (low-spin d⁶, S=0) and in dichloromethane solution they show intense MLCT transitions in the visible region. The two bromide ligands have been replaced from the coordination sphere of [Os(PPh₃)₂(phen)Br₂] under mild conditions by a series of anionic ligands L (where L=quinolin-8-olate (q), picolinate (pic), oxalate (Hox) and 1-nitroso-2-naphtholate (nn)) to afford complexes of type [Os(PPh₃)₂(phen)(L)]⁺, which have been isolated and characterized as the perchlorate salt. The structure of the [Os(PPh₃)₂(phen)(pic)]ClO₄ complex has been determined by X-ray crystallography. The PPh₃ ligands occupy trans positions and the picolinate anion is coordinated to osmium as a bidentate N,O-donor forming a five-membered chelate ring. The [Os(PPh₃)₂(phen)(L)]⁺ complexes are diamagnetic and show multiple MLCT transitions in the visible region. The [Os(PPh₃)₂(N-N)Br₂] complexes show an osmium(II)–osmium(III) oxidation (−0.02 to 0.12 V vs. SCE) followed by an osmium(III)–osmium(IV) oxidation (1.31 to 1.43 V vs. SCE). The [Os(PPh₃)₂(phen)(L)]⁺ complexes display the osmium (II)–osmium (III) oxidation (0.26 to 0.84 V vs. SCE) and one reduction of phen (−1.50 to −1.79 V vs. SCE). The osmium (III)–osmium (IV) oxidation has been observed only for the L=q and L=Hox complexes at 1.38 V vs. SCE and 1.42 V vs. SCE respectively. The osmium(III) species, viz. [Os^III(PPh₃)₂(N-N)Br₂]⁺ and [Os^III(PPh₃)₂(phen)(L)]²⁺, have been generated both chemically and electrochemically and characterized in solution by electronic spectroscopy and cyclic voltammetry.     

On the structure of H2Os3(CO)12

Infrared, far-infrared and Raman data are reported and discussed for H₂Os₃(CO)₁₂. ¹³C NMR studies for H₂Os₃(CO)₁₂ are also reported. These data are consistent with a linear arrangement of the three osmium atoms with terminal hydrides occupying equatorial positions on the end osmium atoms.     

Preparation and Characterization of Mixed‐Valent Osmium Hexacyanoferrate/Silicomolybdate Hybrid Films and Their Electrocatalytic Properties

A polynuclear mixed‐valent osmium hexacyanoferrate/silicomolybdate film electrode has been prepared using repetitive cyclic voltammetry. The cyclic voltammograms have been recorded for the deposition of a mixed‐valent osmium hexacyanoferrate/silicomolybdate hybrid film directly from the mixture of Os³⁺, Fe(CN₆)^3?, and SiMo₁₂O₄₀^4? ions from the acidic aqueous solutions. The polynuclear mixed‐valent osmium hexacyanoferrate/silicomolybdate film exhibited four redox couples. The electrocatalytic properties of the osmium hexacyanoferrate/silicomolybdate film electrode have been studied. The modified electrode has shown good electrocatalytic properties towards the oxidation of dopamine, ascorbic acid, epinephrine, norepinephrine, and reduction of IO₃^?, Fe³⁺.     

Kinetic-catalytic determination of osmium by fluorescence quenching with salicylfluorone and hydrogen peroxide

A highly sensitive and selective fluorescence-quenching kinetic method is proposed for the determination of trace osmium(IV), based on the catalytic effect of osmium(IV) on the salicylfluorone (_ex = 510 nm, _em = 535 nm)-H₂O₂ system at pH 9.3–9.6. Using the fixed time method, osmium(IV) in the range 0.008–0.6 ng/ml can be determined. The detection limit is 0.006 ng/ml. Over thirty anions and cations, including other platinum metal ions, do not interfere, even when present in large excess. The method has been applied successfully for the determination of osmium in a series of synthetic mixtures and refined ore with relative standard deviations of 2–6%.     

Synthesis and Structures of cis- and trans-[Os(Bcat)(aryl)(CO)2(PPh3)2]: Compounds of Relevance to the Metal-Catalyzed Hydroboration Reaction and the Metal-Mediated Borylation of Arenes

Support for key steps of the mechanism for the transition metal catalyzed hydroboration reaction is provided by the characterization and reactions of 1 , a cis-(boryl)(aryl) complex of osmium(II ). This compound readily eliminates o-tolylBcat to give the osmium(0) intermediate 2 , which in the presence of HBcat reestablishes the osmium–boron bond by forming 3 . R=o-tolyl, H₂cat=catechol=1,2-(HO)₂C₆H₄.     

Iridium‐ and Osmium‐decorated Reduced Graphenes as Promising Catalysts for Hydrogen Evolution

Renewable energy sources are highly sought after as a result of numerous worldwide problems concerning the environment and the shortage of energy. Currently, the focus in the field is on the development of catalysts that are able to provide water splitting catalysis and energy storage for the hydrogen evolution reaction (HER). While platinum is an excellent material for HER catalysis, it is costly and rare. In this work, we investigated the electrocatalytic abilities of various graphene–metal hybrids to replace platinum for the HER. The graphene materials were doped with 4f metals, namely, iridium, osmium, platinum and rhenium, as well as 3d metals, namely, cobalt, iron and manganese. We discovered that a few hybrids, in particular iridium‐ and osmium‐doped graphenes, have the potential to become competent electrocatalysts owing to their low costs and—more importantly—to their promising electrochemical performances towards the HER. One of the more noteworthy observations of this work is the superiority of these two hybrids over MoS₂, a well‐known electrocatalyst for the HER.     

Sorption–Photometric Determination of Osmium after Its Extraction from the Gas Phase with Silica Gel Chemically Modified with Mercapto Groups

The sorption of osmium(VIII) from H₂SO₄ solutions and from the gas phase with silica gels chemically modified with mercapto or disulfide groups was studied. A procedure is proposed for the sorption–photometric determination of osmium including the oxidation of osmium, the sorption of OsO₄ from the gas phase with silica gel chemically modified with mercapto groups, and the determination of osmium in the sorbent phase by diffuse reflectance spectrometry. The detection limit is 0.5 g of Os per 0.2 g of the sorbent. The calibration plot is linear up to 700 g Os/0.2 g. The relative standard deviation in the determination of more than 15 g is no larger than 6%. The procedure was used for the determination of osmium in standard reference samples of platinum concentrates.     

Spectrophotometric determination of osmium with phthalimide dithiosemicarbazone by means of complex formation and catalytic reactions

Phthalimide dithiosemicarbazone forms a 1:1 complex with osmium at pH 3.3–4.5 (?₄₅₀ = 1.3 · 10⁴ l mol^?1 cm^?1 ) which is applied to the photometric determination of osmium; Beer's law is obeyed for the range 1–12 μg Os ml^?1. The oxidation of the reagent with cerium(IV) is catalyzed by osmium(VIII), and this reaction allows a more sensitive procedure for the determination of osmium; the calibration curve is linear over the range 0.05–0.4 μg Os ml^?1. The interferences in both procedures are described.     

Deposition of osmium and ruthenium thin films from organometallic cluster precursors

Single‐source organometallic precursors based on a number of homometallic clusters as well as heterometallic cluster RuOs₃(CO)₁₃(µ‐H)₂ have been used for the chemical vapor deposition of osmium films and osmium–ruthenium alloy films, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Chemical transformation of cluster osmium thioselenochloride Os<Subscript>3</Subscript>S<Subscript>7</Subscript>SeCl<Subscript>8</Subscript>

The binuclear osmium complex Os₃S₇SeCl₈ was prepared by the reaction of cluster chalcogen chloride K₆Os₂S₂O₆(CN)₈ with an aqueous KCN solution. In the complex, the distance between the osmium atoms is 2.85 Å, and they are linked by μ-SO ₂ ^2? bridges with the OsSOs angle of 75.9°. The osmium coordination number is 6. In the reaction with CN^? ligands under study, the individual fragments of the structure are retained; however, the trinuclear cluster skeleton of Os₃S₇SeCl₈ is destroyed.     

The Coordination Polyhedra OsN n in Crystal Structures

Characteristics of the Voronoi-Dirichlet polyhedra were used to perform the crystal-chemical analysis of 53 compounds containing osmium atoms surrounded by nitrogen atoms. Depending on the metal oxidation state, which varies from Os(II) to Os(VII), the coordination polyhedra formed by osmium atoms can be octahedra or trigonal prisms (OsN₆), square pyramids (OsN₄Os), tetrahedra (OsN₄), or triangles (OsN₃). The parameters of the Voronoi-Dirichlet polyhedra allow one to estimate quantitatively the main stereochemical features of Os atoms, depending on their oxidation state, and in controversial cases, they can be used to determine the oxidation state of osmium in the crystal structures.     

Osmium catalyzed asymmetric dihydroxylation of methyl trans-cinnamate in ionic liquids, followed by supercritical CO2 product recovery

In this work, osmium-catalyzed asymmetric dihydroxylation (AD) of methyl trans-cinnamate was studied. Osmium and chiral ligand catalysts were immobilized in ionic liquid only, without any other reaction solvents, while the recovery of the product was performed by extraction with supercritical CO₂, and compared with results obtained by extractions with organic solvents such as hexane and diethyl ether. In supercritical CO₂ extraction experiments, optimal extraction pressure was found and ionic liquid chosen, so that the highest reaction yields coupled with lowest osmium content in the crude product can be achieved. Finally, recycle experiments of the same (ionic liquid + catalytic system) mixture were successfully conducted. Application of ionic liquids and supercritical CO₂ in osmium catalyzed AD allows for the isolation of the diol basically without contamination with osmium, in high yield and enantiomeric excess, and it makes possible the efficient reuse of ionic liquid solvent and the catalytic system.     

Studies on the separation of osmium by flotation and spectrophotometric determination with Crystal Violet and Malachite Green

A solvent flotation technique was used for the separation of osmium from aqueous solutions in the form of the ion associates of the anionic complexes OsCl^2?₆ and OsCl₂(SnCl₃)^2?₂ with two basic dyes, Crystal Violet and Malachite Green. A sensitive spectrophotometric method for the determination of osmium based on the system osmium-tin(II) chloride—Crystal Violet—cyclohexane (?=2 × 10⁵ l mol^?1 cm^?1) was developed. Aqueous acetone solutions of the ion associate examined obey Beer's law in the range 0.04–1.0 μg Os ml^?1. The relative standard deviation is 1–6%. Ruthenium interferes with the determination of osmium.     

Sensitive spectrophotometric kinetic determination of osmium by catalysis of the pyrogallol red-bromate reaction

Osmium(VIII) is determined by means of its catalytic effect on the oxidation of pyrogallol red (PGR) by potassium bromate at pH 6.0, 30°C and 545 nm. The decrease in absorbance of PGR (2.5 × 10^?5 M) in the presence of KBrO₃ (0.20 M) over a period of 0–150 s is proportional to the concentration of osmium(VIII) over the range 0–1400 ng ml^?1. The limit of detection of osmium was 0.65 ng ml^?1. The precision and accuracy of the method are described. The effects of the presence of 45 cations and anions on osmium determination were studied. The effects of probable interferences were completely removed by a single extraction of osmium as osmium tetraoxide into isobutyl methyl ketone and back-extraction into sodium hydroxide solution.