Ru Os Research Articles

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.

Redox-responsive molecular switches based on azoterpyridine-bridged Ru/Os complexes.

Three new terpyridine-based dinuclear complexes, [(tpy)Ru(azotpy)Ru(tpy)]4+ (tpy = 2,2':6',2''-terpyridine, azotpy = bis[2,6-bis(2-pyridyl)-4-pyridyl]diazene), [(tpy)Os(azotpy)Os(tpy)]4+, and [(tpy)Ru(azotpy)Os(tpy)]4+ were prepared and their electrochemical and photophysical properties investigated. The bridging ligand, azotpy, in these complexes is reduced at less negative potentials than the unsubstituted tpy ligand. These complexes exhibit absorption bands due to the metal-to-ligand charge-transfer transitions both to the unsubstituted tpy ligand and the bridging azotpy ligand, the latter absorption being observed at the lower energy side of the former. These observations are consistent with the lower lying pi* level of the azotpy ligand than that of the tpy ligand. These complexes are nonluminescent, since the excited electron is trapped in this lower lying pi* level of the azotpy ligand in the excited state. Reduction of this bridging ligand by constant potential electrolysis renders the shape of absorption spectra for these complexes nearly identical to those of the parent complexes, [M(tpy)2]2+ (M = Ru, Os). In this reduced state, the homodinuclear Os complex becomes luminescent at room temperature, whereas the homodinuclear Ru complex becomes luminescent at 77 K, thus establishing their photoswitching behavior. The reduced heterodinuclear complex exhibits luminescence from the Os center, which is sensitized by the Ru center in the same molecule as evidenced by the excitation spectra. Thus, the intramolecular energy transfer can be switched on and off by the redox reaction of the bridging component.

Photophysical properties of TiO(2) surfaces modified with dinuclear RuRu and RuOs polypyridyl complexes.

The photophysical properties of nanoporous TiO(2) surfaces modified with two new Ru(II)-(bpt)-Ru(II) and Ru(II)-(bpt)-Os(II) polypyridyl complexes are reported. These dyads have been prepared by a two-step synthetic pathway. In the first step, [Ru(dcbpy)(2)Cl(2)], where dcbpy is 4,4'-dicarboxy-2,2-bipyridyl, was reacted with the bridging ligand 3,5-bis(pyridin-2-yl)-1,2,4-triazole (Hbpt) to yield the mononuclear precursor Na(3)[Ru(dcbpy)(2)(bpt)].3H(2)O. Subsequent reaction of this compound with either [Ru(bpy)(2)Cl(2)] or [Os(bpy)(2)Cl(2)] yields the Ru(II)-Ru(II) and Ru(II)-Os(II) dyads. Electrochemical data, together with time-resolved transient absorption spectroscopy and the investigation of the incident-photon-to-current-efficiency (IPCE), have been used to obtain a detailed picture of the photoinduced charge injection properties of these dyads. These measurements indicate that for the heterosupramolecular triad based on Ru(II)-(bpt)-Ru(II), the final product species obtained upon charge injection is TiO(2)(e)-Ru(II)Ru(III). For the mixed metal Ru(II)-(bpt)-Os(II) dyad, both metal centers inject efficiently into the semiconductor surface and as a result TiO(2)(e)-Ru(II)Os(III) is obtained as a single charge-separated product.

THE CRYSTAL AND MOLECULAR STRUCTURE OF Ru3(CO)9(PPh3)3

The synthesis of tertiary phosphine and phosphite substituted derivatives of M3(CO)12 {M = Ru(1a) Os(1b)} is discussed and the X-ray crystal and molecular structure of the tris-triphenylphosphine substituted ruthenium cluster Ru3(CO)9(PPh3)3 (2a) is reported. Complex 2a crystallises in the monoclinic space group P21/n with cell parameters a = 14.180(9), b = 21.644(14), c = 18.248(10) Å, β = 92.52(5)°, V = 5595(6) Å 3, Z = 4. The structure was solved by full-matrix least-squares methods based on F 2. The refinement converged at R1 = 0.0564, wR2 = 0.2125 for 4857 observed data [F > 4σ(F)].

HIGH-TEMPERATURE STABILITY OF LAURITE AND Ru Os Ir ALLOY AND THEIR ROLE IN PGE FRACTIONATION IN MAFIC MAGMAS

Experiments were performed to establish the stability limits and mineral – sulfide melt partitioning behavior of the platinum-group minerals laurite (Ru,Os,Ir)S2 and Ru–Os–Ir alloy as functions of temperature and sulfur fugacity. Ruthenium-doped experiments yielded laurite up to ~1275 °C at log f (S2) of −2.0, with laurite replaced by Ru alloy at higher temperature. Similar results were observed at log f (S2) of −2 and −1.3 for compositions doped with multiple PGE, except that Ru–Os–Ir alloy coexisted with laurite at T ≤ 1265°C. Laurite and alloy from these latter experiments were found to be Ru–Os–Ir-rich and Pt–Pd-poor, with grains of alloy containing more Os and Ir than laurite, and both phases becoming (Os + Ir)-rich with increasing f (S2). Concentrations of PGE in sulfide liquid saturated with laurite ± lloy were found to be: Ru: 1–13 wt%; Os and Ir: ≤ 0.6 wt%; Pt and Pd: 0.5–4 wt%. The finding that laurite and Ru–Os–Ir alloy are stable at chromian-spinel-based liquidus temperatures indicates that the commonly observed inclusion of these phases in chromian spinel can be interpreted as a primary magmatic texture. High solubilities for Ru in molten sulfide, combined with low intrinsic abundances of the PGE in igneous rocks, suggest that crystallization of laurite or Ru–Os–Ir alloy in the presence of immiscible sulfide liquid is unlikely. Thus, the extent to which PGE-bearing accessory minerals will affect the final distribution of the PGE within an igneous body may be strongly linked to when, or if, saturation in sulfide liquid occurs.

Geochemical and mineralogical characteristics of Fe–Ni- and bauxitic-laterite deposits of Greece

Contiguous vertical sample profiles from Ni-laterite deposits with in situ features (Kastoria, Profitis Ilias, and Tsouka) and allochthonous Ni- and bauxitic-laterite deposits in contact with basement limestone (Nissi) and bauxitic-laterites lying on peridotite (Parhari) were analyzed for major, trace (including Th and U), rare earth and platinum-group elements (REE and PGE, respectively). In addition, minerals with emphasis to chromite grains found as residual components in these laterites, inherited from the ophiolitic parent rocks, were analyzed by microprobe. Low Al 2O 3, TiO 2, REE, Th and U contents are common features of the Kastoria, Bitincka and Tsouka deposits. In contrast, elevated REE contents are present in the karst-type bauxitic- and Ni-laterite ores of Nissi and bauxitic-laterites of Parhari. The bauxitic-laterite deposit of Nissi attains REE contents of thousands parts per million in samples from the contact between the lowest part of the bauxitic-laterite and the footwall limestone. Highest contents of Th and U are found in the bauxitic-laterites, with Th ranging from 4 to 28 ppm and U from 4 to 66 ppm. In general, increasing Al contents are accompanied by elevated Ti, REE, Th and U contents at the Parhari and Nissi laterite deposits. Goethite, is the dominant mineral in all Ni-laterite profiles studied, while boehmite co-existing with goethite is common in the bauxitic-laterites at Nissi and Parhari. Goethite exhibits variable Al contents, while the Al/Fe ratio increases towards the top of the profiles. The PGE concentrations are generally low, ranging from less than 100 ppb to a few hundred parts per billion. The lowest values — lower than in the bedrock — were recorded in the saprolite zone. A certain enrichment in Pt (up to 48 ppb), Pd (7 ppb), and Au (16 ppb) is recorded in the reddish altered peridotite overlying the saprolite zone at Profitis Ilias. The Fe–Ni ore overlying the reddish altered peridotite has the highest Os values (14 ppb), Ir (32 ppb), Ru (66 ppb), Rh (20 ppb), Pt (86 ppb), and Pd (186 ppb). Gold contents are below 36 ppb. An increasing Pt/Pd ratio from 3.0 in Fe–Ni-laterites to 6.0 in bauxitic-laterites is apparent. Both whole rock compositions and mineral chemistry of laterites indicate that major controlling factors of the composition of the bauxitic-laterites are the conditions during transportation/deposition of the weathered material and during diagenesis/metadiagenesis stage rather than parent mafic ophiolitic rocks. The comparison between the primary composition of chromite in the saprolite zone and the overlying Fe–Ni ore may provide evidence for the discrimination between Fe–Ni ore linked to in situ weathering and ore derived by transportation to some extent of clastic and chemical material.

Solvent extraction/anion exchange separation and determination of PGEs (Os, Ir, Pt, Pd, Ru) and Re–Os isotopes in geological samples by isotope dilution ICP-MS

A method is described that allows the separation of Re, Os, Pt, Pd, Ir and Ru for determination by isotope dilution via inductively coupled mass spectrometry (ICP-MS) at pg levels, from the same sample aliquot. Samples are digested in Carius tubes, enabling effective attack of PGEs in a wide range of geological materials, including pure chromite separates. Os is isolated by solvent extraction so that it may be precisely analysed for isotopic ratios by ICP-MS or negative-ion thermal mass spectrometry. When Os is analysed by ICP-MS, sample memory is minimised by using a direct injection nebuliser. Following Os extraction, Re, Pt, Pd, Ir and Ru are separated from their sample matrix by anion exchange chromatography. The method thus enables PGE abundances and Os isotopic ratios to be determined on the same sample dissolution, thereby avoiding problems of sample inhomogeneity when comparing data. Furthermore, analysis of Re for the same sample dissolution makes geochronological studies possible. Total procedural blanks are routinely less than 10 pg/g for all elements except Pt (15 to 25 pg/g). Blanks of less than 1 pg/g can regularly be obtained for Ir and Os. We estimate procedural detection limits (3∗STD deviation) of c. 3 pg/g for Os and Ir, 5 pg/g for Re, Ru and Pd, and 15 pg/g for Pt. Such detection limits permit analysis of most bulk rock geological samples. The method is evaluated by replicate dissolution of a komatiite reference material, WITS-1 [Tredoux, M., McDonald, I., 1996. Komatiite WITS-1, low concentration noble metal standard for the analysis of non-mineralised samples. Geostand. Newsl. 20, 267–276] together with unknowns. For WITS-1, concentrations of Os, Ir and Ru reproduce well, within a factor of 2 of that expected based on sampling theory. Potential heterogeneity for Pt, Pd and Re is identified at the 1 g sampling level used, that may be related to alteration. Replicate analyses of picritic basalts in the 1 to 10 ppb range show average 2 σ reproducibilities of better than 5% for Re, Os, Ir, Pt and Pd, with Ru being better than 10%. This compares very favorably with other analytical techniques. We present data for andesites with Ir and Os at the sub 10 ppt level. As expected, reproducibility decreases as sample concentrations decrease but are sufficient at the 10 ppt level to confidently identify inter-element PGE fractionations. The analytical method works well for a wide variety of rocks types.

Electron and energy transfer within dyads involving polypyridyl-ruthenium(II) and -osmium(II) centres separated by rigid alicyclic bridges

Rigid alicyclic frameworks (often referred to as molracs, relating to the molecular rack nature of the frame) have been used to vary the separation between organic electron-acceptor (quinone) moieties and chromophoric polypyridylruthenium(II) centres, and between metal centres in Ru–Ru and Ru–Os dinuclear complexes. Photophysical studies have allowed a preliminary insight into the effectiveness of such alicyclic structures in mediating intramolecular photoinduced energy and electron transfer. In the chromophore–spacer–quinone dyads, solvent-dependent quenching of the ruthenium(II) MLCT emission was observed and attributed to electron transfer processes. Distance and stereochemical dependencies of the quenching suggested that through-bond coupling was a factor in these systems. In the heterodinuclear systems, the photo-excited ruthenium(II) chromophore underwent intramolecular energy transfer to the osmium(II) component. A through-space Forster dipole–dipole mechanism could adequately account for the rate of the energy transfer process observed.

Platinum–Group Minerals in Podiform Chromitite from the Kamuikotan Zone, Hokkaido, Northern Japan

Abstract: Ru–Os–Ir alloys have been found in two podiform chromitites located at the Chiroro and Bankei mines in the Sarugawa peridotite complex in the Kamuikotan zone, Hokkaido, Japan. This is the first report on the occurrence of PGM (= platinum‐group minerals) from chromitites in Japan. The Ru–Os–Ir alloys most typically form polyhedra associated with other minerals (Ni–Fe alloys and heazlewoodite) in chromian spinel. The PGM are possibly pseudomorphs after some primary PGM such as laurite and are chemically highly inhomogeneous, indicating a low‐temperature alteration origin. This is consistent with intense alteration (formation of serpentine, uvarovite and kämmererite) imposed on the Kamuikotan chromitites. High‐temperature primary PGE (platinum–group elements)–bearing sulfides were possibly recrystallized at low temperatures into a new assemblage of PGM, Ni‐Fe alloys and sulfides. Placer PGM around the peridotite complexes are chemically different from the PGM in dunite and chromitite possibly due to the, as yet, incomplete search for the rock‐hosted PGM. The PGE content in chromitites is distinctly higher in those in the Kamuikotan zone than in those in the Sangun zone of Southwest Japan, consistent with the more refractory nature (Cr# of spinel, up to 0.8) of the former than the latter (Cr# of spinel, 0.5).

Synthesis, electrochemistry and photophysics of rigid norbornylogous-bridged complexes of ruthenium and osmium

A series of rigid phenanthroline-annulated ligands incorporating fused 6-bond norbornane bicyclo[2.2.0]hexane bridges have been synthesized. The resulting dipyridoquinoxaline (dpq) ligands with covalently bound 1,4-naphthoquinone (dpq-6-NQ) or 1,4-benzoquinone (dpq-6-BQ) moieties were treated with cis-[Ru(bipy)2Cl2]·2H2O to yield the [Ru(dpq-6-NQ}2+ and [Ru(dpq-6-BQ)]2+ [Ru = Ru(bipy)2] complexes as PF6– salts. The symmetric bis-annulated dpq-6-dpq ligand was similarly metallated to yield the dinuclear [Ru(dpq-6-dpq)M]4+ [Ru = Ru(bipy)2, M = Ru(bipy)2 or Os(bipy)2] species, whose electrochemistry and UV-Vis absorption spectra are consistent with class I or weakly coupled class II (localised) mixed-valence character and weak through-bond coupling across the norbornylogous bridge. Preliminary photophysical measurements using steady-state emission spectroscopy revealed quenching of the RuII-based 3MLCT emissive state in the [Ru(dpq-6-NQ)]2+ and [Ru(dpq-6-BQ)]2+ complexes, which is assumed to arise from intramolecular electron transfer between RuII* and the electron-accepting quinone groups. In contrast, the efficient quenching of the 3MLCT emissive state observed in [Ru(dpq-6-dpq)Os]4+ is consistent with intramolecular electronic energy transfer (kEET = 1.5 × 107 s–1) between the RuII* and OsII centres.

A new trial to search for isotopically anomalous osmium and ruthenium in fine-grained Ca, Al-rich Allende inclusions by radiochemical neutron activation analysis

The ratios of 184Os 190Os and 96Ru 102Ru in five fine-grained Ca, Al-rich Allende inclusions (CAIs) were determined simultaneously and precisely by radiochemical neutron activation analysis (RNAA). The results show that their deviations relative to the terrestrial chemical reagent are within −1.5%v and 1.9%v for 184Os 190Os and 96Ru 102Ru , respectively. It seems unlikely that the isotopic anomalies of Os and Ru exist at a magnitude of more than ±2% in bulk fine-grained Allende CAIs. Whereas the possibility that the fine-grained Allende CAIs measured in this work do not contain presolar components and thus have normal isotopic compositions cannot be excluded, we believe that our data may most plausibly be interpreted as the anomalies carried by submicron-size metal alloys thought to be the presolar grains were homogenized during the processes of sample digestion and chemical separation. Os and Ru concentrations in five fine-grained CAIs were determined by comparison with the activities of the known amounts of Os and Ru standards, respectively. In contrast to the coarse-grained Allende CAIs, Os and Ru were greatly depleted in these five fine-grained CAIs. The mean enrichment factors of Os and Ru relative to C1 chondrite were 2.82 and 2.99, respectively. In addition, Os is depleted relative to Ru in four of five fine-grained Allende CAIs, and a large fractionation between Os and Ru is observed. The C1 chondrite-normalized Os Ru enrichment factor ranges from 0.23 to 2.50 in five fine-grained Allende CAIs. These results support the non-equilibrium incomplete condensation model for the origin of fine-grained Allende CAIs. It suggests that the fine-grained Allende CAIs probably contain much less hcp alloy grains, and thus the primordial signatures of isotope and Os Ru ratio might more readily survive the equilibrium process than those in coarse-grained Allende CAIs. Consequently, it is undeniable that the fine-grained Allende CAI is one of the most promising hunting grounds to search for isotopically anomalous Os and Ru.

Synthesis and Reactivity of [PPh4][Ru(N)Me3(SSiMe3)], a Ruthenium(VI) Trimethylsilanethiolate Complex

The anionic organoruthenium complex [PPh4][Ru(N)Me3Br] reacts with NaSSiMe3 to give the trimethylsilanethiolate complex [PPh4][Ru(N)Me3SSiMe3], 1. Reactions of 1 with CsF or with PPh4Cl in nitromethane or acetonitrile produce [PPh4][Ru(N)Me3(SH)], 2. The molecular structure of 2 was determined by X-ray diffraction. Complex 1 reacts with [Os(N)(CH2SiMe3)2(μ-Cl)]2 to form a heterobimetallic complex, [PPh4][Me3(N)Ru(μ-S)Os(N)(CH2SiMe3)2(NCCH3)], 3.

Intramolecular triplet energy transfer in alkyne-bridged Ru–Os multinuclear complexes: switching between dipole–dipole and electron-exchange mechanisms

Intramolecular triplet energy transfer occurs from a ruthenium(II) centre to an osmium(II) centre in heteropolynuclear polypyridine complexes at room temperature in acetonitrile solution. When the metal complexes are linked together by way of a butadiynyl bridge (polypyridine = 2,2′: 6′,6″-terpyridine), energy transfer is extremely fast and takes place via Dexter-type (through-bond) electron exchange. This process is facilitated by selective electron donation to the bridging ligand in the MLCT triplet state of the RuII complex, the electron residing in an extended π*-orbital that partially encompasses the bridge. In marked contrast, insertion of a PtII centre into the butadiynyl bridge (polypyridine = 2,2′-bipyridine) serves to inhibit through-bond electron exchange so that triplet energy transfer occurs slowly. It is considered that the PtII centre decreases the magnitude of the electronic coupling matrix element (HDA < 0.2 cm–1) for electron exchange, in part because of the high energy of its LUMO and HOMO states, relative to the butadiynyl bridge (HDA≈ 12 cm–1). The PtII centre, which donates charge to the bridging ligand, also induces localisation of the promoted electron at an unsubstituted 2,2′-bipyridyl ligand in the triplet excited state. The corresponding cis isomer (with respect to the PtII centre) gives a slightly slower rate of intramolecular triplet energy transfer. The importance of Coulombic energy transfer in these systems is discussed.

Preparation, voltammetry, coulometry and electrochemical quartz crystal gravimetry of [Os(bipy)2(PVPS) n ClRu(edta)] redox polymers

Mixed-metal polymers [Os(bipy)2(PVPS)nClRu(edta)](n= 10,15,20) have been prepared by reaction of [Os(bipy)2(PVPS)nCl]Cl coated electrodes with K[Ru(edta)(H2O)](n= 10,15,20) in solutions of various electrolytes (PVPS = polyvinylpyridine–co-styrene, 10% styrene; edta = ethylenediaminetetraacetato; bipy = 2,2′-bipyridyl). Incorporation of the [Ru(edta)]– unit and binding to the pyridine ligands of P VPS takes place with displacement of water from the coordination sphere of the Ru centre. The resulting [Os(bipy)2(PVPS)nClRu(edta)](n= 10,15,20) polymers are reasonably stable, although reduction at –0.4 V causes gradual loss of Ru centres over 1 h. Slow-scan voltammetry (5 mV s–1) of thin films in aqueous and acetonitrile solvents confirms the approximate 1:1 Os: Ru stoichiometry. Charge-transport characteristics have been investigated by chronocoulometry and rotating disk voltammetry. The behaviour of [Os(bipy)2(PVPS)nCl]X towards other anionic complexes has been investigated: [Mo(CN)8]4– and [Fe(bathophen)3]4–(bathophen = 4,7-diphenyl-l,10-phenanthrolinedisulfonate) bind electrostatically to [Os(bipy)2(PVPS)nCl]X. Ion-exchange studies of the mixed Os-Ru polymers towards complex anions and cations shows that methyl viologen (MV2+) induces a decrease in the electroactivity of the covalently bound [Ru(edta)]– units, and additionally, a decrease in the electroactivity of the Os sites. The fraction of electroactive Os sites in the thick films is increased by the presence of coordinated Ru owing to an enhanced rate of charge transport. No evidence was found that reduction of the [Ru(edta)]– units of the mixed Os-Ru polymer induces incorporation of MV2+; instead, loss of [Ru(edta)(H2O)]– from the polymer rather than MV2+ incorporation dominates. Oxidation of the [Os(bipy)2Cl]+ units of the mixed Os-Ru polymer does, however, induce incorporation of [Fe(bathophen)3]4–; alternatively, quaternization of the polymer dramatically increases its affinity for anions. It is possible to incorporate MV2+ and [Fe(bathophen)3]4– simultaneously, yielding a multiple redox polymer containing six different redox states. In aqueous 0.1 mol dm–3 NaNO3 solution in the absence of added Ru complex, quartz crystal microbalance experiments show rapid loss of the Ru complex from the polymer, leaving an Os polymer which takes up anions on oxidation. In acetonitrile solvent the stability of the attached Ru is much greater and quartz crystal microbalance experiments suggest that the mixed Os–Ru polymer shows a mass increase on Ru reduction, associated with both cation ingress and anion egress. The RuIII/II potential in acetonitrile becomes more negative, indicating stronger preferences of the polymer and cations for the oxidized Ru IIhalf of the redox couple.

Strategies for the assembly of homo- and hetero-nuclear metallosupramolecules containing 2,2′ : 6′,2″-terpyridine metal-binding domains

A new strategy for the convergent synthesis of metallosupramolecular oligomers has been elaborated. The key step is the formation of the ligand-complexes[Ru(X-terpy)(dpqtpy)][PF6]2(X-terpy = terpy, eoterpy, cterpy or msterpy) from the reaction of [Ru(X-terpy)Cl3] with 6′,6″-di(2-pyridyl)-2,2′ :4′,4″ :2″,2‴-quaterpyridine (dpqtpy) in ethane-1,2-diol. These complexes have one non-co-ordinated terpyridine (terpy) domain, and reacted instantaneously with iron(II) salts to give the heterotrinuclear complexes [(X-terpy)Ru(dpqtpy)Fe(dpqtpy)Ru(X-terpy)][PF6]6. Similar reactions with cobalt(II) acetate gave the paramagnetic d7 cobalt(II) complexes [(X-terpy)Ru(dpqtpy)Co(dpqtpy)Ru(X-terpy)][PF6]6 which may be oxidised to the kinetically inert diamagnetic d6 cobalt(III) complexes [(X-terpy)Ru(dpqtpy)Co(dpqtpy)Ru(X-terpy)][PF6]7. The reaction of [Ru(X-terpy)(dpqtpy)][PF6]2 with ‘RuCl3·nH2O’ yielded the homotrinuclear complex [(terpy)Ru(dpqtpy)Ru(dpqtpy)Ru(terpy)][PF6]6. The ruthenium–osmium heterodinuclear complex [(terpy)Ru(dpqtpy)Os(terpy)][PF6]4 was readily obtained from the reaction of [Ru(terpy)(dpqtpy)][PF6]2 with [Os(terpy)Cl3]. Some representative mixed-ligand homodinuclear complexes [(X-terpy)Ru(dpqtpy)Ru(Y-terpy)][PF6]4 containing both electron-releasing and electron-withdrawing terminator ligands were prepared from the reaction of [Ru(X-terpy)(dpqtpy)][PF6]2 with an equimolar quantity of [Ru(Y-terpy)Cl3]. The specific examples with mixed terminator ligands were [(terpy)Ru(dpqtpy)Ru(dmterpy)][PF6]4, [(terpy)Ru(dpqtpy)Ru(msterpy)][PF6]4 and [(dmterpy)Ru(dpqtpy)Ru(msterpy)][PF6]4. All of the compounds were fully characterised, and detailed spectroscopic, spectrometric and electrochemical studies are described.

Refractory inclusions from the Leoville, Efremovka, and Vigarano c3v chondrites: Major element differences between types A and B, and extraordinary refractory siderophile element compositions

We have measured the bulk major and trace element compositions often CAIs from Leoville, Efremovka, and Vigarano, members of the reduced subgroup of C3V chondrites, by INAA. Like CAIs from the reduced subgroup studied previously and unlike CAIs from Allende, a member of the oxidized subgroup, nine of the ten CAIs studied here possess only small amounts of secondary phases and, hence, preserve their pre-alteration bulk major element compositions. Using those compositions and model pre-alteration compositions of Allende CAIs, we cannot distinguish Type B1s clearly from B2s, nor some CTAs from FTAs. All Type As and most Type Bs have superchondritic CaO Al 2O 3 ratios, suggesting that their precursors condensed from a solar gas after ~20% of the Al was removed by high-temperature, Al-rich phases. Type Bs possess higher concentrations of MgO and SiO 2 than do Type As because the precursor phases of Type Bs reacted with the cooling nebular gas to form fassaite, while those of Type As did not. Eight of the ten CAIs have unusual or unique refractory trace element characteristics compared to those seen in Allende inclusions. Vig1, L2, Ef1, and Ef2 have remarkably high concentrations of Re and Os (~57–145 × Cl) because they sampled 4–9 times more hcp condensate metal alloy than did most Allende inclusions. Vig1, L2, Ef1, Ef2, L1, and Vig2 have unusually large Os Ru ratios (up to 6.9 × Cl) because the removal temperatures of their hcp alloy precursors were unusually high (up to ~ 1655 K at 10 −3atm). L2 and L4 have low Zr Hf ratios (~0.4 × Cl); L1 and Ef2, low V/Yb ratios (~0.25 × Cl); Ef2, high Th La (~1.6 × Cl), and Sr Yb (~-2.4 × Cl) ratios; and ED, high Hf Lu (~2.6 × Cl), Sc Lu (~3.1 × Cl), and Zr Lu (~2.8 × Cl) ratios. Most of these fractionations are explained by non-representative nebular sampling of one or more of hibonite, zirconium oxide, perovskite, and melilite, which may be condensates or evaporation residues. Of twenty-five inclusions from the reduced subgroup now studied in this laboratory, seventeen have at least one pair of refractory trace elements which are more fractionated relative to one another compared to Cl chondrites than are the same elements in Allende CAIs, indicating that the host phases of these elements were not as thoroughly mixed together in the nebular region where CAIs of the reduced subgroup accreted as where those in Allende did. Parts of the nebula sampled by C3V chondrites of the reduced subgroup were not well sampled by Allende, and vice versa. Like most coarse-grained inclusions from the reduced subgroup studied previously, most of those analyzed here have lower concentrations of Na, Au, Fe, Zn, and Mn than their Allende counterparts, consistent with the idea that they experienced secondary alteration at a higher temperature or for a shorter time than did Allende inclusions.

Synthesis and electrical conductivity of bridged macrocyclic manganese complexes

Phthalocyaninato( μ- s-tetrazine)manganese(II) [PcMn(tz)] n and 2,3-naphthalocyaninato( μ- s-tetrazine)manganese(II)[2,3-NcMn(tz)] n were synthesized by reacting phthalocyaninatomanganese (PcMn) and 2,3-naphthalocyaninatomanganese (2,3-NcMn), respectively, with tetrazine (tz) in chloroform. In addition, the corresponding pyrazine-bridged systems [PcMn(pyz)] n and [2,3-NcMn(pyz)] n were also prepared for comparison. All compounds were characterized by spectroscopic and TG/DTA methods. The absorption spectrum of [2,3-NcMn(tz)] n shows a weak absorption band in the near infrared region (1700–2100 nm). This band is assigned to metal (manganese)-to-bridging ligand (tetrazine) charge-transfer transition, based on the estimation of energy obtained from the difference between the oxidation potential of manganese naphthalocyanine and the reduction potential of tetrazine. Contrary to other tetrazine-bridged compounds, [MacM(tz)] n (Mac = 2,3-Nc, Pc; M = Fe, Ru Os), the electrical conductivity of the bridging manganese(II)-tetrazine complexes are low despite the high-lying HOMO of manganese and the low-lying LUMO of tetrazine.

Synthesis, x-ray structure, and spectroscopic and electrochemical properties of novel heteronuclear ruthenium-osmium complexes with an asymmetric triazolate bridge

The heterodinuclear compounds ((bpy){sub 2}Ru(bpt)Os(bpy){sub 2})(PF{sub 6}){sub 3} (RuOs) and ((bpy){sub 2}Os(bpt)Ru(bpy){sub 2})(PF{sub 6}){sub 3} (OsRu), where Hbpt = 3,5-bis(pyridin-2-yl)-1,2,4-triazole and bpy = 2,2{prime}-bipyridine, have been prepared and characterized. The crystal and molecular structures of ((Ru(bpy){sub 2}){sub 2}(bpt))(CF{sub 3}SO{sub 3}){sub 3}{center dot}4H{sub 2}O and ((bpy){sub 2}Ru(bpt)Os(bpy){sub 2})(CF{sub 3}SO{sub 3}){sub 3}{center dot}4H{sub 2}O have been determined. Only one of the two possible geometrical isomers of the ruthenium dinuclear compound was found in the crystal structure. The two metal centers are coordinated via N(1) and N(4) of the triazole ring. The metal-metal distance is 6.184 (2) {angstrom}. The NMR data revealed that the OsRu isomer has a similar structure, but with the osmium center bound via N(1) and the ruthenium ion coordinated via N(4) of the triazole ring. The electrochemical potentials of the two heterodinuclear compounds are significantly different; for the RuOs compound the oxidation potentials are 0.73 and 1.20 V, while for the OsRu isomer the oxidation potentials are at 0.65 and 1.30 V vs SCE. These differences in electrochemical behavior between the two isomeric RuOs and OsRu compounds suggest that the N(1) atom of the triazole ring is a better {sigma}-donor than N(4). The mixed-valence dinuclear systems all exhibit rathermore » intense intervalence transition (IT) bands in the near-infrared region, suggesting a moderately strong metal-metal interaction for the bpt systems. A correlation between the energy of the IT bands of the mixed-valence dinuclear complexes and the oxidation potentials has been observed.« less

Chemical compositions of siderophile element-rich opaque assemblages in an Allende inclusion

Ten opaque assemblages, or Fremdlinge, weighing 0.17–19 μg, from an Allende Type B, Ca-, Al-rich, coarse-grained inclusion were analyzed by INAA for Ca, Na, Mn, Sc, Ta, Ti, V, Cr, Fe, Ni, Co, W, Re, Os, Ir, Mo, Ru, Pt, Rh, Au, As, Sb and Se. Refractory siderophiles are usually enriched by factors of 10 3–10 4 relative to Cl chondrites, but not uniformly. From sample to sample, C1 chondrite-normalized Re Os , Ir Pt , Os Ru and Pt Rh ratios vary from 0.81–1.03, 0.70–>2.25, 0.67–3.32 and 0.45–1.43, respectively. Attempts to model the abundances of refractory siderophiles by condensation from the solar nebula into a single phase, assuming ideal solution, fail to match the observed combination of subchondritic Re Os and Ir Pt ratios, even allowing for fractionation of the highest-temperature condensates. A different model, in which all metals whose high-temperature crystal structures are hcp condense into one alloy, bcc into another and fcc into a third, is capable of matching virtually all refractory siderophile fractionations in these Fremdlinge. In this model, all isostructural metals are assumed to form ideal solutions with one another and metals of different structure are assumed to be insoluble in one another. After fractionation of high-temperature hcp and fcc alloys, individual proto-Fremdlinge formed by mixing of high- and low-temperature varieties of each of the three alloys, either in the nebula before and during CAI accretion, or during later partial melting of the silicate, oxide and metal components of CAIs.

Emission characteristics and surface composition of dispenser cathodes in realistic vacuum

The emission characteristics of three types of dispenser cathode, i.e. Ir coated, OsRu coated and uncoated have been studied under realistic vacuum. The cathodes were installed in electron guns normally used for CRT. The emission current was measured in dc method under controlled gas pressures of Ar, N 2, or H 2 at 10 −9 to 10 −6 torr. In cases of Ar and N 2, significant decrease in emission current was observed for each cathode. The onset pressure for the emission decrease was several 10 −8 torr for coated cathodes and several 10 −7 torr for uncoated cathodes. For coated cathodes, the Ir coated cathode has been confirmed to have greater tolerance to the gases than the OsRu coated one. In the case of the H 2, no significant decrease in emission current was observed. The surface compositions of cathodes during and after sputtering by Ar ion were observed by SAM. The results showed the differences in the manner of sputtering away of Ba(−O) layer for three types of cathode.