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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.

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 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+.

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 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 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.

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 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.

The analysis of NMR spectra for Os(II) complexes shows the consistency of structural formulations with relaxation time period and H-D coupling constant values. The complex (Os(bpy)(PPh3)2(CO)(H2))2+ is strongly acidic, as a result of which H2 is prone to heterolytic cleavage and undergoes ready deprotonation. The H2 ligand does not undergo deuterium exchange since it is strongly bound to the central metal atom. Another dicationic complex (Os(bpy)2(CO)(H2))2+ on spectral analysis shows lesser activity of H2 towards heterolytic cleavage and a higher rate of deuterium exchange.

Previous research has established a general method for the preparation of osmium complexes. This method is used to prepare osmium complexes of 1,4,7-triazacyclononane and 1,4,7-trimethyl-1,4,7-triazacyclononane. The substitution and redox chemistry of these complexes are determined. Also determined is the X-ray crystal structure of a salt containing the pi-arene complex.

The synthesis and characterization of neutral and anionic osmium carbonyl clusters are described. The scheme involves the reductive carbonylation or hydrogenation of OsCl3 or alpha-(Os CO sub 3 Cl2)2 supported on silica in the presence of alkali carbonates. The selectivity of the reaction has been found to be influenced by the alkali carbonate added to silica, temperature reaction time and the gas-phase composition.

The reaction of the dihydrido-olefin complex OsH2(eta2-CH2=CHEt)(CO)(P(super i)Pr3)2 with H2SiPh2 produced OsF3(SiHPh2)(CO)(P(super i)Pr3)2. The complex also reacted with H2GePh2, H2GePh3, and HGEt3 to form trihydrido-germyl derivatives, and with HSnPh3 and HSn(super n)Bu3 to form trihydrido-stannyl derivatives. The orientation of the ligand around the osmium atom was similar in all three products with the resulting structure described as a severely damaged pentagonal bipyramid. All compounds were fluxional in solution with the hydrido ligands exchanging positions.

The synthesis and characterization of bimetallic complexes (tpy)(M)(tpp)(RuCl3) (PF6) and (tpy)(M)(tpp)Ru(tpp) (PF6)4, where tpy = 2,2':6',2'-terpyridine; tpp = 2,34,5,6-tetrakis(2-pyridyl)pyrazine; M = RuII or OsII, are presented. The scheme involves a building block approach starting at the tpy end of the molecule, with the components being added in a sequential series of synthetic steps. The complex systems were found to possess long-lived excited states at room temperature with lifetimes of ca. 100 ns.

Metalation of bis(diphenylphosphino)osmium(II) complex produces a series of 1,2,4,5-tetrakis(diphenylphosphino)benzene-bridged Os(II)-M(II) (M = Ni, Pd, Pt) dimetallic complexes. Cyclic voltammetric and spectroscopic studies of these complexes reveal the existence of significant interaction between metal centers in the excited states of the complexes and of moderate interactions in the ground states of these complexes. Comparison of these dimetallic complexes with corresponding monometallic complex indicates the lower quantum yields and shorter excited state lifetimes of the dimetallic complexes, and these observations support the strong electronic coupling between metal centers.

Structural studies of OsH5L(sub 3)(super +) (L=PMe2Ph) by neutron diffraction experiments reveal the compound to be a dodecahedral pentahydride with H/H separations as short as 1.49 angstroms. Labeling studies help determine the mechanism of olefin hydrogenation and the hydroformylation reactions of OsH5(sub 3)(super +). Variable-temperature spectroscopic studies and X-ray diffraction help determine the structure of OsH(C2H4)2L(sub 3)(super +). Extended Huckel calculations reveal the absence of trans influence on Os-C bond lengths in the olefin cation.

Single-crystal X-ray studies help determine the structure of Rb3Os2Br9, a confacial diosmium nonahalide. The internal geometry of this 10 d-electron system agrees with the sigma character of metal-metal interactions. A comparison of SCF-X(alpha)-SW calculations for (Os2Br9)(2-) and (Ru2Br9)(3-) supports high metal-metal interactions in Rb species. Optical spectroscopic studies of (Os2Br9)(3-) and (Ru2Br9)(3-) reveal that both include an electron-exchange term to the order of 8000 per cm.

Nitrogen atmosphere helps prepare bis(acrylic acid)tetraammineosmium(II) bis(hexafluorophosphate). NMR spectrum and elemental analysis demonstrate the bis-substituted formulation. Acid-base titrations determine pKa values. Spectrophotometric measurements determine the rate of aquation. Magnetic susceptibility measurements reveal the paramagnetic nature of the products obtained in the acid catalyzed aquation.

Luminescence and UV absorption of specific dinuclear complexes comprise osmium(II) and ruthenium(II)terpyridine type chromophores. The Ru yields Os energy transfer step exothermically, which corresponded with an exchange-type mechanism. A rigid biocyclometalating ligand bridged the two metal centers in the dinuclear complex.

Studies of polynuclear Os(II)/Ru(II) polypyridine complex luminescence behavior reveals a decanuclear complex with six Os2+ and four Ru2+ metal ions. In compounds possessing both components, only the Os-based luminescence is seen in the 850 - 1000 nm spectral region. The intercomponent energy transfer in the polynuclear metal complexes may lead to supramolecular structures with controlled energy migration patterns.

A dihydrogen derivative, (OsCl(eta 2-H2)(H2bim)(P-i-Pr3)2)Cl is obtained by the reaction of 2,2'-biimidazole (H2bim) with the dihydrido-dichloro complex OsH2Cl2(P-i-Pr3)2. X-ray investigation techniques are used in the determination of the molecular structure of the derivative. When the derivative is subjected to a triclinic space group, the addition of dichloromethane molecule crystallizes the derivative. Dihydrogen ligands are present in the derivative.

The reaction of nitridoosmium(VI) complexes with tertiary phosphines yields stable nitridoosmiun(VI) phosphine complexes. Without metal reduction, neutral complexes are thermally stable and immune to excess phosphine. Chloride ligands abstract in Os(N)-(CH2SiMe3)2(PMe3)2Cl and Os(N)-(CH2SiMe3)2(dppe)Cl, yielding cationic phosphine complexes.

Studies on Os(II) chromophores containing 2,3,5,6-tetrakis(2-pyridyl) pyrazine(tpypz) reveal that the complexes contain a bridging ligand with a very high energy metal-to-ligand charge transfer (MLCT) excited state. The tpypz systems have room temperature excited state lifetimes of up to 200 nanoseconds. The tpypz ligand in the Os(II) complexes is nonbridging and bound to a single metal center. The high MLCT values for the tpypz system validates its use as building blocks for supramolecular systems.

Aqueous media reveal the presence of an *OsVIO2(tmc)2+/OsVO2(tmc)+ pair, whose properties are determined. The aqua-ion quenchers reveal a steady behavior and a self-exchange rate. Small anions participate in the self-exchange rates of numerous pairs, and their properties are determined by employing a highly oxidizing excited state. The quenching data and the halogen pairs reveal different self-exchange rates. A powerful electronic reaction is assumed to participate in the interaction between the halides and the outer-sphere pairs.

The homobimetallic Os(II) complexes of the type (((bpy)2Os)2(BL))4+, where bpy = 2-2'-bipyridine and BL = bridging ligand, were synthesized and characterized. The polyazine compounds 2, 3-bis(2-pyridyl)quinoxaline, 2,3-bis(2-pyridyl)pyrazine and 2, 3-bis(2-pyridyl)benzoquinoxaline were used as bridging ligands in the synthesis. Spectroscopic and electrochemical analyses show that adding a second metal center to the (Os(bpy)2(BLT))2+ parent specie would result in the shifting of the metal-to-ligand charge-transfer absorption maxima to lower energies and a decrease in the bridging-ligand-based reduction potential.

The synthesis and characterization of ((PP3)OsH(eta2-H2))BPh4 and related mono- and dihydrido complexes are described. A rare example of a cis-hydride-eta1-O-OCRR complex is obtained. H/D isotope exchange reactions showed the Os complex to be more acidic than acetone and the reaction may proceed by a keto-enol tautomerization of acetone as catalyzed by the Os complex. This mechanism involves a proton transfer to acetone, resulting in the formation of a dihydride. Extraction of deuterium results in an equilibrium mixture.

The synthesis, electrochemistry and absorption spectra of the complexes (bpy)2M(dpt-cy'-dpt)M(bpy)2(super 4+) and (bpy)2M(dpt-cy')2+ (M = Ru2+, Os2+; bpy = 2,2'-bipyridine; dpt-cy'-dpt = trans-1,4-cyclohexanebis(N4- 3,5-bis(2-pyridyl)-1,2,4-triazole)amide; dpt-cy' = N4-cyclohexane-3,5-bis(2- pyridyl)-1,2,4-triazole) were reported. The potential applicability of the synthesized compounds as multielectron transfer catalysts can be attributed to the weak interaction of the metal units across the cyclohexyl-bridged spacer.

The reaction of Os2(O2CCH3)4Cl2 and 2-phenylbenzoic acid yielded Os2(2-PBZ)4Cl2 (2-PBZ = 2-phenylbenzoate ion). The structure consisted of two independent but essentially identical molecules with the inner core Os2(O2C-)Cl2 possessing D4h symmetry. The magnetic susceptibility plot for the complex showed a slightly greater paramagnetism compared with other Os2(O2CR)4X2 (R = CH3, C2H5, C3H7; X = Cl) compounds. The magnetic susceptibility and electronic structure of Os2(hp)4Cl2 were also determined for comparison.

Two geometrical isomers of (OsL2(PPh3)2)PF6.nH2O, a green (1) and red one (2), were obtained from the oxidation of OsL2(PPh3)2 by cerium(IV). Complex 1 was formed on a large proportion compared to 2 which constituted only about 1 percent. Complex 1 consisted of cations of single type with the atoms occupying general positions while 2 had two almost identical cations. The donor pair triad (N,N)-(S,S)-(P,P) was cis-cis-trans in 1 and trans-trans-trans in 2. The reduction potentials and distortion parameters of the complexes were compared.

The reaction of Os3(CO)12 with phosphine ligands L (L = PMe3, PMe2Ph) gave (Os(CO)4L), (Os(CO)3L2) and (Os(CO)3L3)3. The reaction of methyl iodide with Os(CO)4L yielded (Os(CO)4LCH3)I and with Os(CO)3L2, (Os(CO)3L2CH3)I was obtained. The two products in non-halide solution react to form Os(CO3)LCH3I and Os(CXO)2L2CH3I. The structures were characterized by X-ray diffractometric analysis.

Ruthenium and osmium complexes containing tetra-2-pyridyl-1,4-pyrazine (tppz) ligands were prepared and characterized using electrochemical measurements and fast atom bombardment massspectrometry. The tppz ligands effectively functioned as bridges in forming dimetallic and trimetallic complexes. Results showed that the monometallic complexes were luminescent at both room and very low temperatures. In addition,varying metal-based oxidation potentials in the metal centers of dimetallic andtrimetallic complexes indicated the occurrence of metal to metal interactions along the tppz bridge.

The reactivity of the octahedral compounds MH(eta2-H2BH2)(CO)(PiPr3)2, where M = Os or Ru, toward electrophiles such as HBF4, Hpz, and R*CO2H, where pz = pyrazole and R* = (S)-CH(NaphOMe)Me, (R)-CH(OMe)Ph, (R)-C(CF3)(OMe)Ph, (S)-CHOC(double bond-O)CH2CH2, is reported. Results reveal that these octahedral compounds are catalyst precursors for hydrogen transfer reactions from 2-propanol to unsaturated organic substrates. These compounds are also precursors to six-coordinated hydridocarbonylosmium and -ruthenium compounds with the triisoprpopylphosphine ligand.

X-ray structure determination of the monomeric dialkoxymetalloporphyrins diethoxy-, diphenoxy- and bis(2-propanolato)(meso-tetraphenylporphyrinato)osmium(IV) is reported. These were synthesized from the reaction of Os(Por)(N2)(THF), where Por = TPP or (MeO)12TPP, with alcohols in THF. Os(TPP)(OEt)2, Os(TPP)(OCH(CH2)2)2 and Os(TPP)(OPh)2 are characterized by an Os atom occupying the distorted porphyrin plane. The dpi(Os)-ppi(O) interaction is used to account for the Os-Or distances of 1.915(4), 1.909(4), 1.909(4) and 1.983(2) A, which are shorter than a normal Os-O single bond.