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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.

Application of a dipyrido[3,2-a:2',3'-c]phenazine (DPPZ)-type metal complex as an DNA electrochemical probe was studied. The introduction of electron-donating groups (N[H.sub.2]) was effective for controlling the redox potential and binding affinities of the DPPZ-type osmium complex. The [[Os[(DA-bpy).sub.2]DPPZ].sup.2+] complex (DA-bpy; 4,4'-diamino-2,2'-bipyridine) had a lower half-wave potential ([E.sub.1/2]) of 147 mV (vs Ag|AgCl) and higher binding affinity with DNA (binding constant, K = 3.1 x [10.sup.7] [M.sup.-1]) than those of other complexes. With a single-stranded DNA immobilized gold electrode, the hybridization signal ([DELTA]I) of the [[Os[(DAbpy).sup.2]DPPZ].sup.2+] complex was linear in the concentration range of 1.0 pg [mL.sup.-1] - 0.12 [micro] g [mL.sup.-1] for the targeted DNA with a regression coefficient of 0.999. The detection limit was 0.1 pg [mL.sup.1]. The 400-bp yA[L.sub.3] gene was also detected with good sensitivity and selectivity using the [[Os[(DAbpy).sub.2]DPPZ].sup.2+] complex.

The general model for arc-type basalt genesis is that subducted plates reach a certain depth and release their fluids in a series of dehydration reactions. The fluid migrates into the overlying mantle wedge and initiates melting. High [sup.187]Os/[sup.188]Os ratios in some arc magmas have been attributed to this fluid. Although this interpretation follows logically from the general model for arc-type basalt genesis, it is not supported by experimental data or by Re, Os, or Cl data for arc-type basalt, eclogites, and peridotites. Our new data for basaltic rocks from the Mexican volcanic belt together with data from several other arcs lead us to propose that subduction fluids contain only minimal Re, Os, and CI, and therefore that [sup.187]Os/[sup.188]Os is not increased significantly in the melts above 0.145. The observed low Re concentrations are best explained by initiation of arc-basalt melting in the garnet stability field. Retention of Re by garnet in the source will deplete arc-type basalts in Re relative to oceanic-island basalt and mid-ocean-ridge basalt. Radiogenic Os measured in many arc-type basalts is most likely due to crustal interaction rather than a subduction fluid with high and radiogenic Os concentrations. Keywords: osmium, arc basalt, calc-alkaline, subduction, assimilation.

Research has been conducted on the reaction of porphyrins with osmium tetraoxide. The effect of the electron-donating and electron-withdrawing substituents on these porphyrins has been investigated.

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.

Electrode density effects on the heterogeneous electron-transfer dynamics of monolayers containing osmium, were examined.

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.

Research has been conducted on the mer-M(H) (sub)3 (NO)L (sub)2 (M = Ru, Os) molecules. The characterization of these molecules has been carried out.

MO2 dioxide molecules are important products of an experiment where laser-ablated rhenium, osmium and ruthenium atoms reacted with O2 in excess neon and argon during condensation.

Pyridine-based osmium complexes bearing either a carboxylate or aldehyde group were covalently attached to glucose oxidase and were shown to work as mediators for the reoxidation of the enzyme. For the complex containing the carboxylate group, the binding was made through carbodiimide coupling to the amine residues in the protein. For the complex containing the aldehyde group, the reductive coupling was carried out by condensation with the amino groups on the protein in the presence of sodium cyanoborohydride. Electrochemical studies show evidence for both intramolecular and intermolecular redox mediation for the electrochemical reoxidation of the modified glucose oxidases in the presence of glucose. The modified enzymes adsorbed on glassy carbon and platinum show different electrochemical responses for the two electrode materials, suggesting that orientation of the adsorbed enzyme is induced due to the interaction of the osmium complex with the different surfaces. Construction of enzyme switches based on these modified enzymes was carried out, and their responses were compared with those obtained using native glucose oxidase and a soluble redox mediator.

Research has been conducted on the azavinylidene nitrogen-carbon bond formation. The description of the metal nitrite redox reaction is presented.

Research has been conducted on the reducible ligands azopyridines to investigate osmium. Isolation of nonradical congeners formed via electrochemical/chemical oxidation is discussed.

Research has been conducted on the reaction of cis-[M(bpy) (sub)2 Cl (sub)2] and Os(II) with triazine. The formation of dinuclear complexes as a result of this reaction is described.

Research has been conducted on the osmium(VI) nitrido complexes that contain Schiff base ligands. The results of their synthesis in the presence of 2,6-dimethylpyridine are described.

Research has been conducted on the localized-to-delocalized mixed-valence in osmium mixed-valence complexes. The use of infrared and near-infrared measurements in different solvents is described.

Research has been conducted on the osmium-(VI)-bridged macrocycles. Results indicate that they assemble spontaneously due to the mix of olefins, osmium tetraoxide and bispyridyl ligands in CHCl (sub)3.

The use of quantum mechanical reference data to develop a transition state force field for the AD reaction is demonstrated. The force field is validated by prediction of experimental enantioselectivities and by comparison to energetic and structural data.

Research has been conducted on the Ru(II) and Os(II) complexes with a polyphosphine/cumulene spacer. The synthesis, redox characteristics, electronic interactions and X-ray photoelectron spectroscopic study are described.

The article discusses a new approach to the synthesis of mixed-metal ligand-bridged nuclear complexes. The technique to form rigidly linked [ML (sub)2-(rigid spacer)-M'L (sub)2] compounds is described.

Research has been conducted on the triosmium dinitrido-bridged compounds. The preparation of these compounds via the terminal nitrido complex thermolysis is described.

Research was conducted to examine the inner-sphere cluster formation by (Ru(NH3)5H2O)3+ or (Os(NH3)5H2O)3+ in combination with (M(CN)6)4- (M = Fe, Ru, or Os). The electrochemical behavior of the multinuclear centers in close proximity was also investigated. Results demonstrate that when acid is present to eliminate the adverse effect of internal proton transfer, the rate increase is only a factor of 1.5 or so while in the case of protonated anion about cation, the rate increase is a factor of 3.3. Findings provide insight into the stabilization of (M(CN)6)4- relative to (M(CN)6)3- by (M'(NH3)5)3+ and the stabilization by (M(CN)6)4- of (M'(NH3)5)3+ relative to (M'(NH3)5)2+.

A study was conducted to explore the design and construction of a molecular level electronic set, a set of molecular-level systems capable of performing functions which mimic those of macroscopic components in electronic devices. Nine rodlike compounds of nanometric dimension of the general formula [M(bpy)3-(ph)(sub n)-M'(bpy)3]4+ (M = M' = Ru(II); M = M' = Os(II); M = Ru(II), M' = Os(II); bpy = 2,2'-bipyridine; ph = 1,4-phenylene; n = 3,5,7; the central phenylene unit bears two alkyl chains for solubility reasons). Experimental methods, results and conclusions are discussed.

A study was conducted to analyze an osmium and N-methylmorpholine (NMM)-catalyzed dihydroxylation wherein NMM is reoxidized by m-CPBA. 1H and 13C nuclear magnetic resonance spectra were obtained at 400 and 100.6 MHz, respectively. Products were prepared by chromatography on silica gel. Moreover, a syringe pump was utilized for slow additions. Results indicated that N-methylmorpholine N-oxide can be regenerated in situ in the osmium-catalyzed dihydroxylation.

The relationship of energy-transfer rates and spectroscopic character in the double-complex salts (M(bpy)3)2(Cr(CN)6)Cl.8H2O, where M2+ = Ru2+, Os2+; bpy = 2.12'-bipyridine, has been investigated. The results showed that the luminescence from 3CT state of (M(bpy)3)2+ is partially quenched by (Cr(CN)6)3- at 77 degrees Kelvin and room temperature. The quenching is attributed to intermolecular excitation energy transfer from 3CT state of (M(bpy)3)2+ to the 2Eg state of (Cr(CN)6)3-.

The vibrational spectra of the binuclear propene complexes: [Os2(CO)8(mu2-eta1,eta1-C2H3CH3)]16, its (3,3,3-d3) and (d6) deuterium-substituted isotopologues and [Os2(CO)4(mu2-C2H3CH3)] were determined and the vibrational modes of the alkene ligands had been designated. It was hoped that the effort can be related to the electron energy loss spectroscopy or the reflection-absorption infrared spectroscopy of ethene-osmium complexes chemisorbed on metal single-crystal surfaces.

Combined Ir, Os, Cu, and S concentrations from 18 eastern Australian peridotite xenoliths demonstrate systematic variations in Os concentrations with S loss and require a late-stage process capable of fractionating Os from the geochemically similar Ir. This effect accounts for the greater variability and lower mean Os concentrations observed in peridotite xenoliths as compared with massif peridotites and abyssal peridotites. Late-stage mobility of Os in xenoliths has important implications for interpreting Os isotopic data, and strong correlations between Cu/S and Ir/Os may provide a method for screening Re-Os data to provide more reliable Os isotopic model ages. The ability of cryptic secondary processes to fractionate some platinum-group elements (PGEs), in this case Ir and Os, must be taken into account before attributing fractionated PGE patterns in xenoliths to primary mantle processes.

The reduction-oxidation properties of some ruthenium and osmium complexes were investigated to determine the unusual coordination mode of thiosemicarbazone ligand. Thiosemicarbazones of benzaldehyde and two para substituted benzaldehydes were used to synthesize ruthenium and osmium compounds as well as characterize their structure. Empirical results showed that steric bulk of triphenylphosphine is not a factor in the observed unusual coordination mode of the benzaldehyde thiosemicarbazone ligands.

A study was conducted relating to the investigation of the degree and mechanism of electronic interaction between two redox active metal centers linked by a redox-active bridging ligand of well-defined structure. Specifically, this experiment reports the investigation into the effects of electronic interactions in homo- and heteronuclear ruthenium and osmium bisbipyridyl fragments bridged by O,N-coordination to 1,4-dihydroxy-2,5-bis(pyrazol-1'-yl)benzene (p-L).

The dihydroxylation of commercial polyenes using phenylboronic acid, N-methylmorpholine N-oxide (NMO) and osmium tetroxide in anhydrous solution was described. Narasaka's modified version of the Upjohn procedure for catalytic osmylation was modified wherein water was replaced by phenylboronic acid as the agent for stripping the diolate from the osmium in the NMO/OsO4 dihydroxylation process. Results showed that the chemical reactions could be run at low temperatures due to the absence of water in the solvent mixture.

The wide-angle X-ray scattering technique was successfully used to examine the structure of solid pure osmium phthalocyanine. The solid amorphous material consists of dimeric units (PcOs)2 linked by a direct Os-Os double bond and stacked in columns to form couples of discrete assemblies of formula ((PcOs)2)n. (PcOs)2 is the first example of an Os(II)-Os(II) dimer subjected to a combined structural and magnetic study. Results also affirm that both ruthenium and osmium phthalocyanine could also be dimeric.

The reactivity between trans-[OsVI(tpy)(Cl)2(N)]+ (1) and N3- was investigated. The reaction of 1 with N3- in acetone occurred by electron transfer to give trans,trans-(tpy)(Cl)2-OsII(N2)OsII(Cl)2(tpy). In CH3CN, the compound formed trans-OsII(tpy)(Cl)2(N2) but underwent solvolysis to give trans-OSII (tpy)(Cl)2(CH3CN). Excess N3- in CH3CN reacted with 1 resulting in the formation of OsIII(tpy)(Cl)2(5-CH3-tetrazolate). Furthermore, 1 reacted in the presence of CS2 to give trans-[OsII(tpy)(Cl)2 (NS)]+, SCN- and N2.

The solvation and solvent isotope effects on the radiationless decay rates of the intersystem crossing path (ISCP) from the metal-to-ligand charge transfer (MLCT) state were evaluated through the utilization of the osmium(II) complexes. The solute-solvent interaction and hydrogen bonding of the solvent in water-dioxane and water-methanol mixtures were also studied. The solvent effect for the Os(II) complexes primarily occurred in the ISCP from the MLCT state. The rate of energy transfer was influenced by the hydration structure and the number of water molecules per Os(II) complexes.

A study was conducted on the electrochemistry at very positive potentials in liquid SO2 of RuII and OsII dendritic polynuclear complexes and of several of their lower-nuclearity analogues. The experiments resulted in the observation of several metal- and ligand-centered oxidations which were previously inaccessible. The findings also suggest that the redox properties can also be employed as a powerful tool for the chemical characterization of large and highly charged supermolecules.

A model was developed to analyze and define the properties of an energy transfer from luminescent porous silicon (p-Si) to adsorbed osmium(II) and ruthenium(II) polypyridyl complex compounds. The complex's surface adsorption on p-Si wafers quenched the emission. Facile energy transfer shifts from the surface to Ru(II) and Os(II) complexes. Such transfer is faster and more efficient for Os(II) than for Ru(II).

A study was conducted on the reaction of the complex of [Os(NH3)5(eta2-anisole)]2+ with acetals or Michael acceptors to produce 4-methoxystyrene complexes that are exclusively coordinated at the arene (eta2). These styrene complexes are active dienes and are involved in Diels-Adler reactions with electron-deficient olefins to form tetrahydronaphthalene complexes. The cycloadducts are produced as single diastereomers and are essential as precursors to functionalized tetralins and decalins.

The triosmium clusters Os3(CO)10(N-N) (N-N = alpha-diimine ligand) underwent the reversible formation of biradicals in toluene which last for only a number of nanoseconds and zwitterions in acetonitrile which last for a number of seconds, when exposed to visible light. Photochemical investigations showed that the visibl absorption band of these clusters can be attributed to electronic transitions with Os-to-alpha-diimine charge transfer character with a variable degree of pi-delocalization within the Os(alpha-diimine) moiety.

A study was conducted on the reaction chemistry of osmium porphyrins with thionitrites and alkyl nitrites as well as the mode of interaction of RSNO with osmium porphyrins. The findings indicate that the reactions of thionitrites and alkyl nitrites with OsII porphyrins result in nitrosyl thiolates and alkoxides. However, in the case of OsIII, the isolation is limited to the osmium nitrosyl difluorophosphate complex.

The protonation of corresponding monocationic hydrides yielded the dicationic dihydrogen complexes (Os(H2)(PR3)2(bpy)(CO))2+ (PR3 = PPh3, PMePh2), (Os(H2)(PPh3)2(phen)(CO))2+ and (Ru(H2)(PPh3)2(bpy)(CO))2+. The H2 ligand is strongly bound to the metal center, without any exchange with D2 over a number of weeks. The complex (Os(H2)(PR3)2(bpy)(CO))2+ is very stable in solution at room temperature, while the ruthenium analogue (Ru(H2)(PPh3)2(bpy)(CO))2+ is relatively stable at temperatures below 245 K, although it decomposes in solution at room temperature.

The investigation and synthesization of a series of new Ru(II) complexes containing the carboxylatopyridine ligand moiety were conducted using single-crystal X-ray diffraction, nuclear magnetic resonance, electrospray mass spectrometry, cyclic voltammetry, absorption and emission spectroscopy. Results reveal a general correlation of the electrochemical properties and the number of carboxylate groups per complex.

Reaction of Os3(CO)12 with thionylaniline in refluxing methylcyclohexane results in Os3(CO)9(mu3-NPh)(mu3-S) (1) in good yield. Compound 1 and Os3(CO)9(mu3-eta2-(PhN)2SO)(mu3-S) (2) are produced when Os3(CO)10(NCMe)2 is treated with thionylaniline. Compound 1 reacts with trimethylamine oxide in the presence of acetonitrile to produce Os3(CO)8(NCMe)(mu3-NPh)(mu3-S) (3). Compounds 1-3 were characterized by mass, IR and NMR spectroscopies and their structures were determined by single-crystal X-ray diffraction.

A series of Os-Hg clusters with different Os-Hg metal connectivities located between two (Os(CO)10(mu-X)) (X = Cl, Br, I) subclusters were synthesized via Hg-C bond cleavage of the parent organomercurials. A Os-Hg metal framework with a central collinear Hg-Os-Os-Hg metal backbone was isolated. Results provide new examples of Hg-C bond activation and demonstrate that organomercurials are essential in building up of high-nuclearity clusters.

The electrochemistry of a series of complexes with one or more Cp*Ru+, CpRu+ or CpOs+ fragments (Cp=cyclopentadienyl; Cp*=pentamethylcyclopentadienyl) attached to an oligothiophene pi-system, was investigated. Oxidation of the complexes occurred on the uncomplexed thiophene rings while reduction occurred on the metal. The bound thiophene ring was transformed into a (Cp/Cp*M(thiophene))+ unit and removed from conjugation with the remaining uncomplexed rings.

The coordination of the pentaammineosmium(II) metal center to different kinds of anisoles has been found to radically increase the nucleophilicity of the arene. Reactions occur with a large variety of carbon electrophiles in the presence of acidic acetonitrile at -40 degrees C to produce characterizable 4H-anisolium intermediates. Upon deprotonation and decomplexation, the 4-substituted anisole is returned in overall yields usually greater than 80 %.

The first polyhydrido derivatives that contain donor ligands and which exhibit quantum mechanical exchange coupling between the hydrogen nuclei of the OsH3 group were prepared and characterized. Specifically, OsH6(P(sup i)Pr3)2 was reacted with 2,2-biimidazole (H2biim) to obtain the trihydrido OsH3(Hbiim)(P(sup i)Pr3)2. The latter's quantum mechanical exchange coupling was increased via reaction with the dimers (M(mu-OMe)(COD))2 to replace the acidic proton of the (Hbiim)- ligand with the metallic M(COD) where M = Rh,Ir. This resulted in the heterobimetallic complexes (P(sup i)Pr3)2H3Os(mu-biim)M(COD).

Two-dimensional NMR spectroscopy was employed to investigate the kinetics of coupled two electron/halide transfer reactions between (Cp2MX)+ and Cp2M where M = Ru,Os and X = Cl,Br in CD3CN at 298 K. The results demonstrated a strong dependence of the exchange rate on the identity of the halide atom on the order of I > Br > Cl and Ru > Os. In addition, the reactant state free energy ordering was found to be Cl < Br < I.

A value for the osmium isotopic composition of the modern 'primitive upper mantle' (PUM), a hypothetical undifferentiated upper-mantle reservoir, is reported. A minimum (super 187)Os/(super 188)Os ratio for PUM of 0.1290 +/- 0.0009 is derived from suites of melt-depleted mantle xenoliths from three continents through a correlation between (super 187)Os/(super 188)Os and geochemical indices of 'fertility' to extrapolate to the Os isotope ratio of undepleted mantle. A comparison with the (super 187)Os/(super 188)Os ratios in different classes of chrondritic meteorite leads to the conclusion that the late veneer has siderophile element abundances similar to those of enstatite or ordinary chrondrites.