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The Triassic-Jurassic (T-J) boundary ca. 200 Ma represents one of the major mass extinction events of the Phanerozoic; however, the cause of this event remains controversial because of a paucity of geological evidence. In this study we present an isotopic record of osmium extracted from a bedded chert succession across the T-J boundary in the Kurusu section of Japan, deposited within a Paleo-Pacific (Panthalassa) deep basin. The data show a gradual decrease in seawater [sup.187]Os/[sup.188]Os values during the Rhaetian, followed by a sharp increase in the latest Rhaetian, and a subsequent stable phase across the T-J boundary. The decreasing trend of [sup.187]Os/[sup.188]Os values during the Rhaetian indicates a gradual increase in the relative supply rate of unradiogenic Os from the mantle associated with emplacement of the Central Atlantic Magmatic Province. The subsequent shift toward radiogenic values reflects an increased supply of radiogenic Os due to enhanced continental weathering. This interval marks more negative isotopic values of organic carbon, the onset of radiolarian faunal turnover, and conodont extinctions, indicating that the rapid increase in continental weathering rate was closely linked to the perturbation of the carbon cycle and the T-J biotic crisis. doi: 10.1130/G31223.1

Whether the downgoing slab in modern subduction zones is able to melt is an important unresolved aspect of plate tectonics. Rare arc lavas with high Sr/Y ratios and low Y and heavy rare earth element concentrations, called adakites, are often attributed to melting of young subducted crust in subduction zones. Osmium isotopic data obtained for 13 adakite samples from Mindanao, Philippines, conflict with the slab-melting model. Ten of the samples have unradiogenic [sup.187Os]/[sup.188Os] ratios inconsistent with partial melting of the ca. 50 Ma Philippine Sea lithosphere subducting beneath Mindanao. The Os isotope signatures are similar to those of young mid-oceanic-ridge basalts and normal arc rocks, consistent with a mantle source. In addition to implications for mass transfer in subduction zones, the apparent association of adakites with Cu-Au deposits makes understanding their origin, and that of the associated metals, economically interesting. This study suggests that a reevaluation is required of the slab-melting hypothesis in general, and that the metals associated with the Mindanao adakites come from the mantle. Keywords: adakites, osmium, Philippines, subduction.

Byline: V. N. Losev (1), Yu. V. Kudrina (1), A. K. Trofimchuk (2), P. N. Komozin (3) Abstract: The sorptive extraction of osmium(VIII, VI, IV) from HCl solutions with silica gels chemically modified with mercapto groups (MPS) and disulfide groups (DPDSS) was studied. The recovery of osmium(VIII) from 0.5--4 M HCl is [proportional to]99 and [proportional to]25% with the sorption equilibration time 5 and 20 min for MPS and DPDSS, respectively. The equilibration time for the extraction of Os(VI) with MPS is no longer than 1 min. The recovery from 0.1--4 M HCl is up to 99.9%. The recovery of osmium(VI) with DPDSS decreases from 96 and 80% when going from 0.5 M to 4 M HCl. The quantitative extraction of osmium(IV) is attained at 95degC in the presence of tin(II) chloride and the equilibration time 60 min. Without tin(II) chloride, osmium(IV) is not extracted with these sorbents. The difference in the sorption ability of chemically modified silica gels with respect to osmium in different oxidation states can be used for the extraction of osmium(VI) and osmium(IV) and their separate determination directly in the MPS phase with the use of diffuse reflectance spectrometry. Author Affiliation: (1) Research Engineering Center Kristall, Svobodnyi pr. 79, Krasnoyarsk, 660041, Russia (2) Shevchenko National University, Vladimirskaya ul. 64, Kiev, 01033, Ukraine (3) Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 117223, Russia Article History: Registration Date: 06/10/2004

The deposition of a 30-[Angstrom]-thick layer of iridium upon a 250-[Angstrom]-thick osmium reflective layer for use as a diffraction grating in the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) satellite observatory has provided sufficient protection from an expected maximum orbital atomic-oxygen fluence of 1 x [10.sup.16] atoms/[cm.sup.2]. The grating parameters of groove constant and depth, efficiencies of zeroth-order, first and second inside orders, and first inside-order efficiency positional uniformity as well as stray light near the first inside order of the Ir-Os-coated grating were measured within a CHIPS spectral bandpass of 90-260 [Angstrom]. Stray-light measurements were also made near the first inside spectral order at 304, 584, and 1216 [Angstrom]. The results make the Ir-Os coat an acceptable grating reflectivity layer for CHIPS and other spaceborne extreme-ultraviolet spectrometers that employ grazing-incidence reflection optics. OCIS codes: 050.2770, 290.5820, 310.1620, 310.6860.

The mono(acetylacetonato) complexes [MCl(O,O'-acac) ([[eta].sup.6]-arene)] (M = Ru, Os, arene = [C.sub.6][H.sub.6], 1,3,5-[C.sub.6][H.sub.3][Me.sub.3], [C.sub.6][Me.sub.6]; M = Os, arene = 1,2-[C.sub.6][H.sub.3][Me.sub.2], 1,2,3-[C.sub.6][H.sub.3] [Me.sub.3]), which are formed from [[M[Cl.sub.2] ([[eta.sup.6]-arene)].sub.2] and thallium or sodium acetylacetonate, react with thallium acetylacetonate to give bis(acetylacetonato) complexes [M(O,O'-acac)([[eta].sup.1]-acac)([[eta].sup.6]-arene)]. The [[eta].sup.1]-acac ligand is bound through the [gamma]-carbon atom for M = Ru, Os, arene = [C.sub.6][H.sub.6]; M = Os, arene = 1,2-[C.sub.6][H.sub.4][Me.sub.2], 1,2,3-[C.sub.6][H.sub.3][Me.sub.3] and through a keto-oxygen atom for M = Ru, Os, arene = 1,3,5-[C.sub.6] [H.sub.3][Me.sub.3], [C.sub.6][Me.sub.6], the difference being attributed to a combination of steric and electronic effects. Cationic ruthenium(II) derivatives [Ru(L)(O,O'-acac)([[eta].sup.6]-arene]+ (arene = [C.sub.6][H.sub.6], 1,3,5-[C.sub.6][H.sub.3][Me.sub.3], [C.sub.6][Me.sub.6]; L = DMSO, MeCN, py, P[Ph.sub.3]) and [Ru(CO) (O,O-acac)([[eta].sup.6]-arene]+ (arene = 1,3,5-[C.sub.6][H.sub.3] [Me.sub.3],[C.sub.6][Me.sub.6]), and neutral osmium(II) [[eta].sup.1]-acetato derivatives [Os([[eta].sup.1]-OAc) (O,O'-acac) ([eta].sup.6]-arene)] (arene = [C.sub.6][H.sub.6], 1,2-[C.sub.6] [H.sub.4][Me.sub.2], 1,2,3-[C.sub.6][H.sub.3][Me.sub.3], 1,3, 5-[C.sub.6][H.sub.3][Me.sub.3], [C.sub.6][Me.sub.6]) are also described. The molecular structures of the following complexes have been determined by X-ray crystallography: [Os(O,O'-acac) ([[eta].sup.1]-C-acac)([[eta].sup.6]-1,2-[C.sub.6][H.sub.4] [Me.sub.2])], triclinic, space group P [bar]1 (No. 2), a = 9.922(2), b = 9.974(2), and c = 11.001(2) [Angstrom], [alpha] = 68.33(1), [beta] = 64.18(1), and [gamma] = 62.38(1)[degrees], V = 849.0(3) [Angstrom], Z = 2; [Os(O,O'-acac)([[eta].sup.1]-O-acac)([[eta].sup.6]-1,3, 5-[C.sub.6][H.sub.3][Me.sub.3])], monoclinic, space group C2/c (No. 15), a = 16.032(4), b = 11.989(3), and c = [2.sub.1].562(7) [Angstrom], [beta]= 108.91(2)[degrees], V = 3921(2) [Angstrom], Z = 8; [Os([[eta].sup.1]-OAc)(O,O'-acac)([[eta].sup.6]-[C.sub.6][H.sub.6])], triclinic, space group P [bar]1 (No. 2), a = 8.368(4), b = 8.402(4), and c = 11.008(4) [Angstrom], [alpha] = 71.68(3), [beta] = 69.35(3), and [gamma] = 69.77(3)[degrees], V = 663.0(6) [[Angstom].sup.3] Z = 2. Key words: arene-ruthenium, arene-osmium, acetylacetone, crystal structures.

Reaction of [Os[O.sub.4]] with [C.sub.7][H.sub.7]MgBr ([C.sub.7][H.sub.7] = 2-methylphenyl) followed by column chromatography afforded the reported osmium tetraaryl [Os([[C.sub.7][H.sub.7]).sub.4] along with the oxo-osmium(VI) ([OsO([[C.sub.7][H.sub.7]).sub.4]]) (1) (13%) and the dioxoosmium(VI) ([Os[O.sub.2]([[C.sub.7] [H.sub.7]).sub.2]]) (2) (25%) complexes. Treatment of [Os[O.sub.4]] with [C.sub.8][H.sub.9]MgBr ([C.sub.8][H.sub.9] = 2,5-dimethylphenyl) gave a mixture of [Os([[C.sub.8][H.sub.9]).sub.4]] (3) (34%) and [OsO ([[C.sub.8][H.sub.9]).sub.4]] (4) (4%) while that with [C.sub.8] [H.sub.9]OMgBr ([C.sub.8][H.sub.9]O = 4-methoxy-2-methylphenyl) afforded [OsO([[C.sub.8][H.sub.9]O).sub.4]] (5) in 20% yield. Oxidation of 3 with 3-chloroperoxybenzoic acid afforded 4 in good yield. The solid-state structures of 1 and 4 have been established by X-ray crystallography. Crystals of 1 are tetragonal with a = 13.080(1) and c = 6.6506(5) [Angstrom] V = 1137.9(1) [[Angstrom].sup.3], Z = 2, and space group of P4/n; while those of 4 are tetragonal with a = 13.593(2) and c = 7.377(2) [Angstrom], V = 1363.0(5) [[Angstrom].sup.3], Z = 4, and space group of P4/n. The geometry around osmium in both complexes is square pyramidal with the oxo ligand occupying apical position. The Os--O and Os--C distances in 1 are 1.652(2) and 2.084(1) [Angstrom], respectively, while those in 4 are 1.688(7) and 2.088(4) [Angstrom] respectively. The cyclic voltammograms of the monooxo aryl osmium(VI) compounds show reversible Os(VI/V) couple at around -1.4 V vs. ferrocene/ferrocenium couple. Key words: osmium(VI), oxo aryl complexes.

The fluoride ion acceptor properties of OsO4 and OsO3F2 were investigated and the OsO4F(super -) anion was fully structurally characterized in the solid state by vibrational spectroscopy and by a single-crystal X-ray diffraction study of [N(CH3)(sub 4)][OsO4F]. The geometries and vibrational frequencies of the OsO2F(super -), cis-OsO4F(sub 2)(super 2-), and fac-OsO3F(sub 3)(super -) anions are calculated using density functional theory.

Peridotite xenoliths from the Cascade arc in the United States and in the Japan arc have neodymium and osmium isotopic compositions that are consistent with addition of 5 to 15 percent of subducted material to the present-day depleted mantle. These observations suggest that osmium can be partitioned into oxidized and chlorine-rich slab-derived fluids or melts. These results place new constraints on the behavior of osmium (and possibly other platinum group elements) during subduction of oceanic crust by showing that osmium can be transported into the mantle wedge., Studies of the isotopic compositions and large-ion lithophile and light element abundances of arc lavas (1-3) have shown the importance of recycled subducted material in the genesis of arc magmas. [...]

Calculations with data for asteroidal cores indicate that Earth's outer core may have a rhenium/osmium ratio at least 20 percent greater than that of the chondritic upper mantle, potentially leading [...]

Rhenium and osmium concentrations and the osmium isotopic compositions of iron meteorites were determined by negative thermal ionization mass spectrometry. Data for the IIA iron meteorites define an isochron with an uncertainty of approximately ± 31 millioon years for meteorites 4500 million years old. Although an absolute rheniumosmium closure age for this iron group cannot be as precisely constrained because of uncertainty in the decay constant of [sup.187.Re], an age of 4460 million years ago is the minimum permitted by combined uncertainties. These age constraints imply that the parent body of the IIAB magmatic irons melted and subsequently cooled within 100 million years after the formation of the oldest portions of chondrites. Other iron meteorites plot above the IIA isochron, indicating that the planetary bodies represents by these iron groups may have cooled significantly later than the parent body of the IIA irons., IRON METEORITES ARE DIVIDED INTO groups on the basis of their internal structures and chemical compositions. In most instances, irons of the same group were likely derived from the same [...]

The structural and exchange bias properties of CoFe/IrMn prepared on Si (100) and Si (111) with an Os/Cu buffer layer were investigated. Since the Os (0002) surface mesh has the same atomic arrangement as fcc (111) orientation, and the lattice mismatch between Os (0002) and IrMn (111) is as low as 2.6%, the CoFe/IrMn grown on H-Si(100) showed a strong IrMn (111) diffraction peak, while a very weak IrMn (111) peak appeared on H-Si (111). With increasing Os thickness (do s), the IrMn (200) peak was weakened, while the IrMn (111) became strong on H-Si (100). For the CoFe/IrMn grown on H-Si(111), no obvious structural change appeared. Os plays an important role on tuning the IrMn to result in the exchange bias. On the other hand, CoFe/IrMn showed an exchange field ([H.sub.ex]) on both H-Si(100) and H-Si(111) with the Os buffer layer; however, the magnetization switching process was different due to different the crystalline degree. A sharp magnetization switching process occurs for IrMn(111) on Os/Cu/H-Si(100) with a square hysteresis loop. A 370 and 310 Oe of [H.sub.ex] was found in textured CoFe/IrMn on Os/Cu/H-Si(100) and Os/Cu/H-Si(111), respectively. Index Terms--Buffer layer, osmium, textured film.

Iridosmine grains from placer deposits associated with peridotite-bearing ophiolites in the Klamath mountains have extremely radiogenic [sup.186]Os/[sup.188]Os ratios and old Re-Os minimum ages, from 256 to 2644 million years. This indicates the existence of an ancient platinum group element reservoir with a supra-chondritic Pt/Os ratio. Such a ratio may be produced in the outer core as a result of inner core crystallization that fractionates Os from Pt. However, if the iridosmine Os isotopic compositions are a signature of the outer core, then the inner core must have formed very early, within several hundred million years after the accretion of Earth., Osmium has two radiogenic isotopes, [sup.186]Os and [sup.187]Os. [sup.190]Pt decays to [sup.186]Os with a half-life of ~449.4 billion years (Gy) (1), and [sup.187]Re decays to [sup.187]Os with a half-life of [...]

Two depth profiles of the osmium concentration and the [sup.187]OS/[sup.186]OS isotopic ratio in the Indian Ocean showed that the osmium concentration seems to be unaltered by chemical or biological processes occuring in seawater; accordingly, osmium is conservative. These data were obtained from an experimental method that eliminated the problems related to osmium preconcentration. This method led to a new evaluation of the concentration of osmium in seawater; the mean concentration of osmium and the [sup.187]Os/ [sup.186]Os ratio are equal to 10.86 ± 0.07 picograms per kilogram and 8.80 ± 0.07, respectively. The results suggest the existence of an organocomplex that dominates the speciation of osmium in seawater., The [sup.187]Os/[sup.186]Os ratios in marine sediments are considered to indicate the relative variations of continental, mantle, and meteoritic input to seawater and to provide a record of continental weathering. However, [...]

The synthesis and structural characterization by NMR and X-ray analysis of various mononuclear, homodinuclear, and heterodinuclear complexes are described, along with the study of their absorption, electrochemical, and near-IR emission properties.

Infrared spectroelectrochemistry explores the vibrational properties of a pyrazine-bridged osmium-polypyridine dimer as a function of its formally metal-centered oxidation states. The infrared spectrum of the mixed-valence complex is quite interesting, exhibiting a highly active totally symmetric mode from the bridging pyrazine ligand (V (sub 8a)) and total coalescence of at least four modes from the peripheral bipyridine ligands.

A remarkably diverse reactivity between the series of nitrido complexes at room temperature is reported. The products depend upon the electron content of the starting nitrido complexes.

An unparalleled chemical transformation of 2-(2',6'-dimethylphenylazo)-4-methylphenol was observed upon its reaction with [M(PPh3)3X2] (M=Ru, Os; X=Cl, Br) whereby one methyl group from the phenyl ring of the arylazo fragment migrates to the metal center through oxidation to carbon mono-oxide.

The mechanism of the addition of osmium tetra oxide, and rhenium (VII) oxides across C=C bonds was controversial. Early work indicated a [3+2] addition, and later kinetic studies suggested, an initial [2+2] addition, whereas recent quantum-chemical calculations showed the [3+2] addition to be favored.

An efficient preparative protocol of 3-D networked osmium nanomaterial is shown by utilizing the capillary action of mesopores of MCM-48 toward molten organometallic precursors as well as high catalytic activity and excellent reusability in certain oxidation reactions. Other 3-D networked nanostructured metals could also be prepared by a similar method.

New divalent osmium complexes that feature strong red metal-to-ligand-charge-transfer (MLCT) phosphorescence and electrophosphorescence are reported. The best external quantum efficiency of 2.2% is achieved when PVN:PBD is used as the host matrix.

The theoretical studies of electronic structures and related chemical properties of isoelectronic complexes M(bpy)(sub 3)(super n+) (M=Re, Os and Ir; n=1,2, and 3, respectively) are carried out with density functional theory (DFT) method at B3LYP/LanL2DZ level.

The unusual transformation of N-arylbenzohydroxamic acids mediated by an osmium complex, [Os(bpy)(sub 2)Br(sub 2), affording a family of cyclometalates of osmium)III) where the transformed hydoxamic acids are coordinated as doubly deprotonated benzanilides are reported. The findings show that benzanilides are capable of functioning as bidentate, C,N-donor ligands.

A series of osmium polypyridyl complexes having various ground-state reduction potentials are synthesized and used to sensitize nanoporous titanium dioxide electrodes to solar illumination, the responses of which are compared with the behavior of their ruthenium analogues. The osmium complexes appear to be promising candidates for further optimization in operating photoelectrochemical cells for solar energy conversion applications.

Given a new tool similar to a hammer, a carpenter will quickly learn how to use it. Learning to use an unfamiliar new tool, on the other hand, takes some [...]