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PubMed1996

In vitro activity and biochemical effectiveness of new organometallic complexes of osmium(III) against Leishmania donovani and Trypanosoma cruzi.

In the present paper, the in vitro activities of 10 osmium(III) complexes with [OSIII(L)] degrees structure against promastigote forms of Leishmania donovani and epimastigote forms of Trypanosoma cruzi haven been assayed. The complexes OSIII-2,4dinitroimidazole dithiocarbamate, OSIII-4-nitroimidazole dithiocarbamate, OSIII-benznidazole dithiocarbamate and OSIII-2-amino-6-Br-benzothiazole dithiocarbamate induced high percentages of growth inhibition in the parasites. The four compounds showed moderate cell toxicity. The inhibitory effects of these complexes on macromolecule synthesis have been evaluated using [3H]-thymidine, [3H]-uridine and [3H]-leucine incorporation. These metal-drug complexes clearly inhibit the DNA, RNA and protein synthesis, as well as the enzymatic activities of succinate dehydrogenase, malate dehydrogenase and pyruvate kinase.

Animals↗
PubMed1976

Isolation of disaturated phosphatidylcholine with osmium tetroxide.

A simple, rapid, inexpensive method for isolating disaturated phosphatidylcholine from adult rat lung has been devised. Total lipids are reacted with osmium tetroxide dissolved in carbon tetrachloride, and the disaturated phosphatidylcholine is isolated on a column of neutral alumina. More than 99% of the fatty acids in the phosphatidylcholine fraction are saturated and 94% of this material migrates as phosphatidylcholine on subsequent thin-layer chromatography.

Animals↗
PubMed2000

Oxygen and Osmium-A New Alliance for Dihydroxylations?

The activation of oxygen in new synthetic procedures dramatically expands the scope of osmium-catalyzed dihydroxylations [Eq. (1)]. Even air can now be used as the cooxidant in the asymmetric version of this reaction with little loss of selectivity.

Journal Article↗
PubMed2002

Electronic energy transfer and collection in luminescent molecular rods containing ruthenium(II) and osmium(II) 2,2':6',2"-terpyridine complexes linked by thiophene-2,5-diyl spacers.

The electronic absorption spectra, luminescence spectra and lifetimes (in MeCN at room temperature and in frozen n-C3H7CN at 77 K), and electrochemical potentials (in MeCN) of the novel dinuclear [(tpy)Ru(3)Os(tpy)]4+ and trinuclear [(tpy)Ru(3)Os(3)Ru(tpy)]6- complexes (3 = 2,5-bis(2,2':6',2''-terpyridin-4-yl)thiophene) have been obtained and are compared with those of model mononuclear complexes and homometallic [(tpy)Ru(3)Ru(tpy)]4+, [(tpy)Os(3)Os(tpy)]4+ and [(tpy)Ru(3)Ru(3)Ru(tpy)]6+ Complexes. The bridging ligand 3 is nearly planar in the complexes, as seen from a preliminary X-ray determination of [(tpy)Ru(3)Ru(tpy)][PF6]4, and confers a high degree of rigidity upon the polynuclear species. The trinuclear species are rod-shaped with a distance of about 3 nm between the terminal metal centres. For the polynuclear complexes, the spectroscopic and electrochemical data are in accord with a significant intermetal interaction. All of the complexes are luminescent (phi in the range 10(-4)-10(-2) and tau in the range 6-340 ns, at room temperature), and ruthenium- or osmium-based luminescence properties can be identified. Due to the excited state properties of the various components and to the geometric and electronic properties of the bridge, Ru --> Os directional transfer of excitation energy takes place in the complexes [(tpy)Ru(3)Os(tpy)]4+ (end-to-end) and [(tpy)Ru(3)Os(3)Ru(tpy)]6+ (periphery-to-centre). With respect to the homometallic case, for [(tpy)Ru(3)Os(3)Ru(tpy)]6+ excitation trapping at the central position is accompanied by a fivefold enhancement of luminescence intensity.

Journal Article↗
PubMed2003

Synthesis and reactions of terminal osmium and ruthenium complexed phosphinidenes [(eta6-Ar)(L)Md=PMes*].

Novel, very stable ruthenium and osmium containing terminal phosphinidene complexes [(eta(6)-Ar)(L)M=Mes*] (Ar=benzene, p-cymene; L=PR(3), CO, and RNC) have been prepared by dehydrohalogenation of novel [(eta(6)-Ar)MX(2)(PH(2)Mes*)] complexes in the presence of a stabilizing ligand. Xray crystal structures are reported for [(eta(6)-C(6)H(6))(PPh(3))Rud=PMes*] (9) and [(eta(6)-pCy)(PPh(3))Os=PMes*] (4). Dehydrohalogenation in the absence of a stabilizing ligand resulted in the new P-spiroannulated Ru(2)P(2)-ring structure 16. Dehydrohalogenation in the presence of but-2-yne gave a novel phosphaallyl complex [(eta(6)-Ar)Ru(eta(3)-R(2)PC(Me)CHMe)] 26, for which an X-ray crystal structure is reported. The mechanism by which 16 and 26 are obtained is presumed to involve the intermediate formation of the 16-electron (eta(6)-benzene)Rud=PMes* phosphinidene complex.

Journal Article↗
PubMed2005

Metal-directed synthesis and photophysical studies of trinuclear v-shaped and pentanuclear x-shaped ruthenium and osmium metallorods and metallostars based upon 4'-(3,5-dihydroxyphenyl)-2,2':6',2''-terpyridine divergent units.

A new series of V-shaped trinuclear metallorods and X-shaped pentanuclear metallostars has been prepared by the reaction of metal complexes bearing pendant phenolic functionalities with complexes containing electrophilic ligands. Specifically, {M(tpy)2} motifs (M=Ru or Os; tpy=2,2':6',2''-terpyridine) bearing one or two pendant 3,5-dihydroxyphenyl substituents at the 4-position of the central ring of the tpy have been reacted with the complexes [Ru(tpy)(Xtpy)]2+ (X=Cl or Br) to form new ether-linked species. The energy transfer from ruthenium to osmium in these complexes has been investigated in detail and the efficiency of transfer shown to be highly temperature dependent; the energy transfer is highly efficient at low temperature, whereas at room temperature nonradiative and nontransfer deactivation of the excited {Ru(tpy)2}* domains is most significant.

Journal Article↗
PubMed1977

An ultrastructural classification of the neuronal cell bodies of the rat dorsal root ganglion using zinc iodide-osmium impregnation.

Zinc iodide-osmium (ZIO) impregnation of rat dorsal root ganglia differentially stained various elements in the neuronal cells, particularly their Golgi bodies. On the basis of this differential ZIO staining dorsal root ganglion neurones have been classified into seven types. The ultrastructure of these is described and the numbers of each type in the L4 dorsal root ganglion have been determined. Prolonged nerve stimulation did not change the relative numbers of the different cell types suggesting that none of the differences between cell types represents differences in their state of activity. The possibility is discussed that differences in morphology may reflect differences in neurotransmitter function.

Animals↗
PubMed2006

Use of tris(2,2'-bipyridine)osmium as a photoluminescence-following electron-transfer reagent for postcolumn detection in capillary high-performance liquid chromatography.

The photoluminescence-following electron-transfer (PFET) technique, developed in our laboratory, is a sensitive chromatographic detection method for oxidizable analytes. Because the oxidations are homogeneous, the technique avoids the problem of electrode fouling. A liquid-phase oxidant reacts with the electrochemically active analytes after separation, becoming capable of photoluminescence. Laser-induced photoluminescence is measured to quantitate the analytes. Thus, the electrochemical properties of the oxidant determine the detection selectivity, and the spectroscopic properties define the sensitivity. The properties of tris(2,2'-bipyridine)osmium (1) were investigated for use as the liquid-phase oxidant in the PFET system. The redox potential of the complex is less positive than that of tris(2,2'-bipyridine)ruthenium (2); thus, on-line generation of 1(3+) by reaction with PbO2, and selective oxidation of catechols by 1(3+), was possible. The mild oxidizing power of 1(3+) led to a lower background signal (compared to 2(3+)) when mixed with acidic mobile phases. Photoluminescence from 1(2+) was much weaker than that from 2(2+); nonetheless, the system achieved subnanomolar detection limits for dopamine, 3-methoxytyramine, and serotonin. Dopamine and 3-methoxytyramine in rat brain striatal dialysates were determined before and after the injection of nomifensine. The pH of the mobile phase can govern the detection selectivity, since oxidation of most organics is accompanied by proton transfer. Reaction of 1 with catechols showed pH-dependent sensitivity resulting from pH-dependent reaction rate changes. Since the reaction rate is also temperature dependent, increased temperature at the mixer resulted in higher sensitivity. However, the noise level also increased at elevated temperature; thus, the detection limit did not improve.

2,2'-Dipyridyl↗
PubMed2003

Preparation and characterization of new ruthenium and osmium containing polyoxometalates, [M(DMSO)3Mo7O24](4-) (M = Ru(II), Os(II)), and their use as catalysts for the aerobic oxidation of alcohols.

A new heptamolybdate polyoxometalate structure containing ruthenium(II) or osmium(II) metal centers, [M(II)(DMSO)(3)Mo(7)O(24)](4-) (M = Ru, Os), was synthesized by reaction between (NH(4))(6)Mo(7)O(24) and cis-M(DMSO)(4)Cl(2). X-ray structure analysis revealed the complexes to contain a ruthenium/osmium center in a trigonal antiprismatic coordination mode bound to three DMSO moieties via the sulfur atom of DMSO and three oxygen atoms of the new heptamolybdate species. The heptamolybdate consists of seven condensed edge-sharing MoO(6) octahedra with C(2v) symmetry. Three Mo atoms are in classic type II octahedra with a cis dioxo configuration. Two Mo atoms are also type-II-like, but one of the short Mo-O bonds is associated with bridging oxygen atoms rather than terminal oxygen atoms. Two molybdenum atoms are unique in that they are in a trigonally distorted octahedral configuration with three short Mo-O bonds and two intermediate-long M-O bonds and one long Mo-O bond. The [M(II)(DMSO)(3)Mo(7)O(24)](4-) polyoxometalates were effective and in some cases highly selective catalysts for the aerobic oxidation of alcohols to ketones/aldehydes. The integrity of the polyoxometalate was apparently retained at high turnover numbers and throughout the reaction, and a variation of an oxometal type mechanism was proposed to explain the results.

Journal Article↗
PubMed2003

Tuning the properties of the osmium nitrido group in TpOs(N)X2 by changing the ancillary ligand.

TpOs(N)(OAc)2 (2) is formed upon reaction of TpOs(N)Cl2 (1) with excess silver acetate (Tp = hydrotrispyrazolylborate). Treatment of 2 with protic acids HX gives the osmium(VI) complexes TpOs(N)X2, where X = trifluoroacetate (TFA, 3), trichloroacetate (TCA, 4), tribromoacetate (TBA, 5), bromide (6), oxalate (X2 = O2C2O2, 7), or nitrate (ONO2, 8). Cyclic voltammetry studies of 1-8 show irreversible reductions of OsVI to OsV, varying over a range of 0.63 V. Much smaller relative variations are observed in 15N NMR chemical shifts, v(Os identical to N) stretching frequencies, and optical absorbances. Compounds 1-8 all react with PPh3 by nucleophilic attack at the nitride ligand, yielding TpOs(NPPh3)X2. The reactions are accelerated by more electron withdrawing ligands X. The relative rates correlate with the peak reduction potentials although the effect is small: the rates vary by only 10(2) while the 0.63 V change in Ep,c corresponds to a change in equilibrium constant for electron transfer of approximately 10(11). Compounds 1-8 also react with triphenylboron, BPh3, with formation of borylanilido complexes TpOs[N(Ph)BPh2]X2. However, rate constants for reactions with BPh3 to yield OsIV boryl-amido complexes do not in general correlate with one-electron-reduction potentials. This is likely due to the mechanism of the BPh3 reactions being a two-step process and not simply nucleophilic attack.

Journal Article↗
PubMed2003

Crystal growth of novel osmium-containing triple perovskites.

Single crystals of two new osmium-containing triple perovskites, Ba(3)LiOs(2)O(9) and Ba(3)NaOs(2)O(9), were grown from reactive molten hydroxide fluxes in sealed silver tubes. They crystallize in the space group P6(3)/mmc with lattice parameters of a = 5.8025(1) A, c = 14.1468(4) A for Ba(3)LiOs(2)O(9) and a = 5.8858(1) A, c = 14.3451(5) A for Ba(3)NaOs(2)O(9). The magnetic susceptibility of these osmates indicates significant Os-Os coupling within the octahedra pair.

Journal Article↗
PubMed2003

Unprecedented chemical transformation of benzaldehyde semicarbazone mediated by osmium.

para-Nitrobenzaldehyde semicarbazone (O(2)N(para)-C(6)H(4)C(H)=N-NH-CO-NH(2)) undergoes unprecedented chemical transformation during its reaction with [Os(PPh(3))(2)(CO)(2)(HCOO)(2)] in different alcoholic (R'OH, R' = CH(2)CH(2)OCH(3), CH(2)CH(3), CH(2)CH(2)CH(3), and CH(2)CH(2)CH(2)CH(3)) solvents whereby the NH(2) group of the semicarbazone ligand is displaced by a OR' group provided by the solvents. The transformed semicarbazone ligand binds to osmium as a bidentate N,O-donor forming five-membered chelate ring to afford complexes of type [Os(PPh(3))(2)(CO)(H)(L-OR')], where L-OR' refers to the transformed semicarbazone ligand. Structure of the [Os(PPh(3))(2)(CO)(H)(L-OCH(2)CH(2)OCH(3))] complex has been determined by X-ray crystallography. All the [Os(PPh(3))(2)(CO)(H)(L-OR')] complexes are diamagnetic and show characteristic (1)H NMR signals. They also show intense absorptions in the visible and ultraviolet region. Cyclic voltammetry on the complexes shows an irreversible oxidative response within 0.69-0.88 V versus SCE.

Journal Article↗
PubMed2004

Ternary rare earth osmium aluminides R(7+)(x)Os(12)Al(61+)(y) belonging to a structural family with layered topology.

The 10 intermetallic compounds R(7+)(x)Os(12)Al(61+)(y) (R = Y, Nd, Sm, Gd-Tm) were prepared by arc-melting of the elemental components. They crystallize with a hexagonal structure very similar to that of Y(7.28)Re(12)Al(61.38). The structure was determined from four-circle diffractometer data of Y(7+)(x)Os(12)Al(61+)(y): P6(3)/mcm, a = 1301.5(2) pm, c = 903.0(2) pm, Z =1. Four atomic sites, all located on the 6(3) axis, show fractional occupancy, resulting in the composition Y(7.86(1))Os(12)Al(61.51(4)), corresponding to the Pearson symbol hP90-8.63. The structure may be viewed as consisting of alternating atomic layers of two kinds, although chemical bonding within and between the layers is of similar character as can be judged from the near-neighbor environments, where all of the 11 atomic sites have high coordination numbers. One kind of layers (A). is relatively loosely packed and contains the yttrium and some aluminum atoms. The other kind (B). consists of the osmium and the remaining aluminum atoms in a nearly hexagonal close-packed arrangement. These layers are stacked in the sequence ABAB. A similar building principle has recently been recognized for several other structures of ternary intermetallic compounds of rare earth and transition metals with a high content of aluminum or gallium, where the structures of CeOsGa(4), Ho(3)Ru(4)Ga(15), and Y(2)Pt(6)Al(15) are the most recent examples. This structural family is briefly reviewed. The cell volume of Yb(7+)(x)Os(12)Al(61+)(y) indicates a mixed or intermediate valence character +2/+3 for the ytterbium atoms of this compound.

Journal Article↗
PubMed2006

Synthesis and characterization of triazenide and triazene complexes of ruthenium and osmium.

Triazenide [M(eta2-1,3-ArNNNAr)P4]BPh4 [M = Ru, Os; Ar = Ph, p-tolyl; P = P(OMe)3, P(OEt)3, PPh(OEt)2] complexes were prepared by allowing triflate [M(kappa2-OTf)P4]OTf species to react first with 1,3-ArN=NN(H)Ar triazene and then with an excess of triethylamine. Alternatively, ruthenium triazenide [Ru(eta2-1,3-ArNNNAr)P4]BPh4 derivatives were obtained by reacting hydride [RuH(eta2-H2)P4]+ and RuH(kappa1-OTf)P4 compounds with 1,3-diaryltriazene. The complexes were characterized by spectroscopy and X-ray crystallography of the [Ru(eta2-1,3-PhNNNPh){P(OEt)3}4]BPh4 derivative. Hydride triazene [OsH(eta1-1,3-ArN=NN(H)Ar)P4]BPh4 [P = P(OEt)3, PPh(OEt)2; Ar = Ph, p-tolyl] and [RuH{eta1-1,3-p-tolyl-N=NN(H)-p-tolyl}{PPh(OEt)2}4]BPh4 derivatives were prepared by allowing kappa1-triflate MH(kappa1-OTf)P4 to react with 1,3-diaryltriazene. The [Os(kappa1-OTf){eta1-1,3-PhN=NN(H)Ph}{P(OEt)3}4]BPh4 intermediate was also obtained. Variable-temperature NMR studies were carried out using 15N-labeled triazene complexes prepared from the 1,3-Ph15N=N15N(H)Ph ligand. Osmium dihydrogen [OsH(eta2-H2)P4]BPh4 complexes [P = P(OEt)3, PPh(OEt)2] react with 1,3-ArN=NN(H)Ar triazene to give the hydride-diazene [OsH(ArN=NH)P4]BPh4 derivatives. The X-ray crystal structure determination of the [OsH(PhN=NH){PPh(OEt)2}4]BPh4 complex is reported. A reaction path to explain the formation of the diazene complexes is also reported.

Journal Article↗
PubMed2006

Osmium(VII) fluorine compounds.

Of the four published osmium fluorine compounds in the oxidation state +7, OsO3F, OsO2F3, OsOF5, and OsF7, only one (OsOF5) is a real Os(VII) compound. OsO(3)F has obviously been OsO4. OsO2F3 in its two modifications is a mixed-valence Os(VI)/Os(VIII) compound, whereas a new compound Os2O3F7 is a mixed-valence OsV/Os(VIII) compound. The molecular structures of OsO3F, OsO2F3, and OsO3F2 are calculated. OsO3F2 seems to exist in two forms, with D3h and Cs symmetry. The original preparation of OsF7 could not be reproduced, only OsF6 has been obtained.

Journal Article↗
PubMed1996

The Osmium(VIII) Oxofluoro Cations OsO(2)F(3)(+) and F(cis-OsO(2)F(3))(2)(+): Syntheses, Characterization by (19)F NMR Spectroscopy and Raman Spectroscopy, X-ray Crystal Structure of F(cis-OsO(2)F(3))(2)(+)Sb(2)F(11)(-), and Density Functional Theory Calculations of OsO(2)F(3)(+), ReO(2)F(3), and F(cis-OsO(2)F(3))(2)(+).

Osmium dioxide tetrafluoride, cis-OsO(2)F(4), reacts with the strong fluoride ion acceptors AsF(5) and SbF(5) in anhydrous HF and SbF(5) solutions to form orange salts. Raman spectra are consistent with the formation of the fluorine-bridged diosmium cation F(cis-OsO(2)F(3))(2)(+), as the AsF(6)(-) and Sb(2)F(11)(-) salts, respectively. The (19)F NMR spectra of the salts in HF solution are exchange-averaged singlets occurring at higher frequency than those of the fluorine environments of cis-OsO(2)F(4). The F(cis-OsO(2)F(3))(2)(+)Sb(2)F(11)(-) salt crystallizes in the orthorhombic space group Imma. At -107 degrees C, a = 12.838(3) Å, b = 10.667(2) Å, c = 11.323(2) Å, V = 1550.7(8) Å(3), and Z = 4. Refinement converged with R = 0.0469 [R(w) = 0.0500]. The crystal structure consists of discrete fluorine-bridged F(cis-OsO(2)F(3))(2)(+) and Sb(2)F(11)(-) ions in which the fluorine bridge of the F(cis-OsO(2)F(3))(2)(+) cation is trans to an oxygen atom (Os-O 1.676 Å) of each OsO(2)F(3) group. The angle at the bridge is 155.2(8) degrees with a bridging Os---F(b) distance of 2.086(3) Å. Two terminal fluorine atoms (Os-F 1.821 Å) are cis to the two oxygen atoms (Os-O 1.750 Å), and two terminal fluorine atoms of the OsO(2)F(3) group are trans to one another (1.813 Å). The OsO(2)F(3)(+) cation was characterized by (19)F NMR and by Raman spectroscopy in neat SbF(5) solution but was not isolable in the solid state. The NMR and Raman spectroscopic findings are consistent with a trigonal bipyramidal cation in which the oxygen atoms and a fluorine atom occupy the equatorial plane and two fluorine atoms are in axial positions. Density functional theory calculations show that the crystallographic structure of F(cis-OsO(2)F(3))(2)(+) is the energy-minimized structure and the energy-minimized structures of the OsO(2)F(3)(+) cation and ReO(2)F(3) are trigonal bipyramidal having C(2)(v)() point symmetry. Attempts to prepare the OsOF(5)(+) cation by oxidative fluorination of cis-OsO(2)F(4) with KrF(+)AsF(6)(-) in anhydrous HF proved unsuccessful.

Journal Article↗
PubMed1998

Mono- and Bis(hydrazine) Complexes of Osmium(II): Synthesis, Reactions, and X-ray Crystal Structure of the [Os(NH(2)NH(2))(2){P(OEt)(3)}(4)](BPh(4))(2) Derivative.

Reaction of OsH(2)P(4) [P = P(OEt)(3), PPh(OEt)(2), PPh(2)OEt] with methyl triflate followed by the treatment with hydrazines gave the [OsH(RNHNH(2))P(4)]BPh(4) (1-3) (R = H, CH(3), C(6)H(5), 4-NO(2)C(6)H(4)) derivatives. Instead, the reaction of OsH(2)P(4) first with methyl triflate, then with triflic acid, and finally with an excess of the appropriate hydrazine afforded the bis(hydrazine) [Os(RNHNH(2))(2)P(4)](BPh(4))(2) (4, 5) (R = H, CH(3), C(6)H(5)) complexes. Also the [Os(NH(2)NH(2)){P(OEt)(3)}(5)](BPh(4))(2) (7) derivative was prepared. All the hydrazine complexes were fully characterized by IR and (1)H and (31)P NMR spectra, and a single-crystal X-ray structure determination of the complex [Os(NH(2)NH(2))(2){P(OEt)(3)}(4)](BPh(4))(2).C(2)H(5)OH (4a) is reported. The compound crystallizes in the space group P2(1)/c with a = 20.550(4) Å, b = 19.663(4) Å, c = 20.843(4) Å, beta = 99.84(9) degrees, and Z = 4. The coordination around the osmium atom is octahedral and the orientation of the ligands in the [Os(NH(2)NH(2))(2){P(OEt)(3)}(4)](2+) cation is determined by several strong hydrogen bonds involving hydrazine nitrogen and phosphite oxygen atoms. Amidrazone complexes [Os{eta(2)-NH=C(R1)N(R)NH(2)}{P(OEt)(3)}(4)](BPh(4))(2) (8, 9) (R = H, CH(3); R1 = CH(3), 4-CH(3)C(6)H(4)) were prepared by allowing nitrile complexes [Os(R1CN)(2)P(4)](BPh(4))(2) to react with hydrazine NH(2)NH(2) or methylhydrazine CH(3)NHNH(2). Reaction of complexes containing substituted hydrazine ligands of the type [OsH(RNHNH(2))P(4)]BPh(4) and [Os(RNHNH(2))(2)P(4)](BPh(4))(2) [P = P(OEt)(3); R = CH(3), C(6)H(5)] with Pb(OAc)(4) at -30 degrees C results in the selective oxidation of the hydrazine affording the corresponding diazene [OsH(RN=NH)P(4)]BPh(4) (10) and [Os(RN=NH)(2)P(4)](BPh(4))(2) (11) derivatives. The first bis(methyldiazene) complex [Os(CH(3)N=NH)(2){P(OEt)(3)}(4)](BPh(4))(2) (11b) was thus prepared.

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