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Previous research has been able to synthesize the high-oxidation-state cyclopentadienyl metal polyhydride known as (pentamethylcyclopentadienyl)osmium(VI) pentahydride. However, whether the complex contains five equivalent hydride ligands or inequivalent hydrides in rapid exchange remains unknown. To remedy this problem, the polyhydride is subjected to ab initio calculations to determine its structure, vibrational spectrum and rearrangement mechanism.

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.

The rotational frequency of the H2 ligand in trans-(Os(H..H)X(L)2)+, where L = phenyl, X = Cl, Br and L = ethyl, X = Cl, is near the Larmor frequency. The complex is octahedral and has an elongated dihydrogen ligand in solid-state and solution. The distance between the hydrogen atoms, d(sub HH), is calculated from coupling constant, J(H,D). The T1(min) value gives the limits for d(sub HH). The acidic character of these complexes is a function of the nature of X ligand.

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. [...]

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.

A study has been conducted to examine the products of osmium-catalyzed asymmetric dihydroxylation reactions. DFT was used to calculate the metallaoxetane ligand complexes. The calculations were compared to those of their corresponding osmium and ruthenium complexes. The results revealed an unusually high level of enantioselectivity. An electrostatic dipole-dipole interaction between the osmaoxetane and the ester moiety of the ligand was also observed.

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 [...]

The monohydride OsHCL(CO)(PiPr3)2 reacts with HCL to form dihydrogen OsCl2(eta squared-H2)(CO)(PiPr3)2. A study of reactivity between hydridoosmium compounds and alkynes shows that specific organometallic compounds can be prepared by reacting these compounds with terminal alkynes when the right number of hydrido ligands and electronic properties of starting material are chosen. New carbene derivatives are produced in the reactions between OsCl2(eta squared-H2)(CO)(PiPr3)2 and terminal alkynes. X-ray crystallography has been used to determine the structure of the carbene derivatives.

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.

Proton and NMR studies of OsH2X2L2 (X = halide and L = PiPr3), synthesized by a halide exchange reaction, show that these molecules exist as two interconverting isomers in solution. One isomer has a C2 symmetry and results from steric interactions between phosphine and chlorine ligands and bonding preference of the chlorine ligands. Replacement of chloride by hydride and slight geometric distortions link the symmetric and nonsymmetric structures.

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.

OsO4 is an efficient catalyst for the stereospecific cis-dihydroxylation of olefins and this asymmetric dihydroxylation (AD) enables the synthesis of diols in quantitative yield. Rate acceleration and selectivity in this nonenzymatic catalyst depend on noncovalent binding, and the AD is an example of 'ligand accelerated catalysis.' Though AD catalysts exhibit few similarities with enzyme catalysts, they exhibit significant selectivity and capacity to produce both enantiomers.

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.

Phenylene spacers connect the Ru(tpy)(sub 2)(super 2+) complex, where tpy is 2,2':6', 2'-terpyridine, and Os(tpy)(sub 2)(super 2+) binding blocks to produce rigid rod-like Ru(II)/Os(II) terpyridine-type complexes. The two building units exhibit slightly different absorption spectra in the dinuclear compounds. Electrochemical measurements of redox potentials reveal metal-metal and ligand-ligand interactions. Time-resolved luminescence spectroscopic analysis of energy transfer reactions shows that electron exchange through the phenylene linker facilitates energy transfer from the Ru-unit to the Os-unit.

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.

Quantum chemical calculations which use effective core potentials calculate spin-spin coupling constants and binding energies of stretched osmium(II) molecular hydrogen complexes. The results agree with experimental data. Population and complex binding energy analyses examine the nature of Os-H2 bonding. The influence of the trans ligand on the properties of the complexes are related to the spectrochemical constant.

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.

X-ray and neutron diffraction, which were used to determine the structure of certain osmium compounds, revealed a cation in the compound having a low J(H-D) value of 9.0 Hertz. The acetate and the H2 ligands of the structure were found at positions on opposite sides of the OsN4 plane and induced an octahedral coordination. The compound's ethylenediamine ligands demonstrated a trans arrangement.

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.

A study was done on the syntheses, absorption spectra, luminescence properties and electrochemical behavior of supramolecular Ru and/or Os complexes of tris(bipyridine) bridging ligands. All the complexes display very intense, ligand centered absorption bands in the UV region and moderately intense metal-to-ligand charge-transfer bands in the visible. Luminescence data show that electronic energy transfer takes place from the Ru-based to the Os-based components.

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.

The reaction of complex cis-(Os(bpy)2(CO)H)+ (bpy = 2,2'-bipyridine) and some related complexes with CO2 in acetonitrile was investigated. The twice- reduced form of the osmium complex was found to be reactive with CO2. Cyclic voltammograms showed a greater current-CO2 concentration proportionality than with H2O. The kinetics of reduction of CO2 by related complexes showed a current increase upon reduction in the bpy wave. Two pathways resulted in the formation of separate intermediates.

The reactions of (mu-H)Os3(CO)10(mu-OCNHCHMe2) with bromine and iodine yield dinuclear compounds (mu-X)Os2(CO)6(mu-OCNHCHMe2)X2 with two halogens in the cis form which in a solution slowly transforms to its trans-isomer. Kinetic studies show that bromide analogue isomerize faster than the iodocomplex, both of which follow first-order rate law. The photodecarbonylation reactions and the crystal structures of the two complexes and their transformation intermediates were also discussed.

Supramolecular systems were synthesized fromthe Os(ttp)2(super 2+) photosynthesizer, the electron donors PTZ and DPAA and the electron acceptor MV2+. The Os(ttp)(super 2+) systems were investigated at low temperature with lifetimes of 4mus for Ru(ttp)2(super 2+) and 540 ns for Os(ttp)2(super 2+). There was no evidence supporting electron transfer quenching for the PTZ-P and DPAA-P dyads. However, exoergonic electron transferquenching in the P-MV2+ dyads resulted in P1+-MV1+.

The addition of (NH4)2OsBr6 to a solution of 2,3-diamino-2,3-dimethylbutane (tmen) resulted in the (Os tmen-H 2 t-men)2+ complex. Likewise, the addition of OsCl3.3H2O to tmen resulted in the chloride complex and its subsequent reaction with CF3SO3H yielded (Os tmen-H tmen 2)(CF3SO3)3.0.5H2O. The pH dependence of the reduction potential of (Os tmen-H 2 t-men)2+ revealed that reduction occurs simultaneously with a gain of two electrons to form the protonated (Os tmen3)2+ complex.

Three osmium tetraoxide (OsO4) fixation methods for studying the microstructure of milkfat globules and its membranes by transmission and scanning microscopy were compared. Commercial dairy whipping cream with agarose gel was treated with glutaraldehyde, OsO4 vapors and a mordant. This was then stained with imidazole buffered OsO4 (IBO), ferricyanide OsO4 (FO) or tricomplex OsO4 (TO). FO- and TO-treated specimens had better contrast and intact milkfat globules and membrane structures than IBO-treated specimens. Transmission electromicroscopy gave realistic micrographs while scanning electromicroscopy gave a more graphic three-dimensional view of the specimens.

The reaction of (OsRh4 CO 15)2- with (Rh CO 2 MeCN 2)1+ or (Rh CO 2 Cl)2 produces the anions (OsRh5 CO 16)1- and (OsRh3 CO 12)1-. The crystal structure of (PPN)(OsRh5 CO 16) consists of (PPN)1+ cations and (OsRh5 CO 16)1- anions in a 1:1 molar ratio. The average metal-metal bond distance is 2.776(3) Angstrom. Meanwhile, the crystal structure of (PPN)(OsRh3 CO 12) consists of (PPN)1+ cations and (OsRh3 CO 12)1- anions in a 1:1 moalr ratio. The anion has a tetrahedral metal skeleton encompassed by 12 carbonyl groups, seven terminal and five bridging all except one of the M-M edges.

The compound (Ru2 chp4 2 pyz)(BF4)2 was prepared from the product of Ru2(chp)4Cl and Ag(CH3CN)4BF4 in dichloromethane dissolved in pyrazine. The compound (Ru2 chp4 py)(BF4).hexane.py was prepared from an analogous manner with pyrizine added to (Ru2 chp4 CH3CN)(BF4). Two diruthenium(II,III) tetrakis(mu-6-chloro-2-hydroxy)pyridinate units with Ru-Ru bond distances of 2.267(1) Angstrom and one axially bridging pyz molecule with Ru(1)-N(pyz) distances of 2.275(5) Angstrom constitute the first compound. Both compounds exhibited similar magnetic behavior and Curie-Weiss behavior.

The complexes Os3(CO)10(NCMe)(Si OR 3)(mu-H) and Os3(CO)11(Si OR 3)(mu-H) were synthesized from the reactions of Os3(CO)10(NCMe)2 and Os3(CO)11(NCMe) with HSi(OR)3, where R = Et and Me. The synthesis of these complexes have proven that trialkoxysilyl ligands may act as triply bridging eta3 ligands in trinuclear complexes via the use of the oxygen atoms from two of the alkoxy groups attached to the silicon. A molecule of Os3(CO)10(NCMe)(SiOEt 3)(mu-H) consists of a cluster of three osmium atoms with nine linear terminal carbonyl ligands distributed around the cluster.

The pyrolysis of Pt2Os3(CO)10(COD)2 at 128 degrees C generated three high-nuclearity platinum-osmium carbonyl cluster complexes. These complexes were Pt4Os6(CO)22(COD), Pt2Os6(CO)21(COD)2 and Pt4Os6(CO)19(COD)2. The cluster of the first complex consists of two Pt3Os3 octahedra sharing the triplatinum triangular face. The mean Pt-Pt and Os-Os bond distance are 2.65 and 2.90 Angstrom, respectively. The second complex has a structure similar to the first except for the bridging CO which is replaced by a Pt(COD) group. The last compound is a meta-bicapped Pt2Os4 octahedron.

The stereochemical nonrigidity of the mu3-benzene/pi-alkene complexes (Os3(CO)8(eta2-CH2CHR)(mu3:eta2:eta2:eta2-C6H6)), where R = H, Me, Ph and (super t)Bu, is investigated using one- and two-dimensional NMR experiments in solution. Of the five processes detected by NMR for the complex with R = H, four are in the solid state. 13C(1H) two-dimensional exchange spectroscopy illustrates a 1,2 ring-hopping motion that alters the nuclei in the face-capping benzene ligands. On the other hand, the pi-bound olefins are fluxional.

Trinuclear metal complexes with benzene in a the face-capping bonding mode mu3:eta2:eta2:eta2-C6H6 are synthesized. The ligand in the triosmium complex Os3(CO)9(mu3:eta2:eta2:eta2-C6H6) is generated from the sequential H-abstraction of the complex (mu-H)Os3(CO)9(mu3-eta2:eta2:eta2-C6H7). The triphenylmethyl cation eliminates the hydride from the dienyl ring in the complex to give ((mu-H)Os3(CO)9(mu3-eta2:eta2:eta2-C6H6))1+. The triosmium complex crystallizes in the space group Im, with the benzene-capped triosmium cluster having a C3v symmetry.

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 phenol-dienone equilibrium for a series of eta2-phenol complexes of pentaamineosmium(II) was examined to investigate the degree of dearomatization in these systems. The complexes with the form (Os(NH3)5(2, 3-eta2-phenol))2+ were characterized by 1H NMR spectroscopy and compared with an anisole derivative. Protonation and deprotonation were favored at the ring face opposite the metal accounting for the stereoselectivity of the tautomerization processes.

The isostructural compounds Y4Br4Os and Er4Br4Os were synthesized and characterized by single-crystal X-ray crystallography. The structures consisted of osmium-centered square antiprisms of the host metals with the bromine atoms capping the four adjoining metal triangles. Magnetic susceptibility data for Er4Br4Os followed the Curie-Weiss law while the yttrium analogue proposed a Pauli magnetism.