Co-C Distances Research Articles

Mechanochemical synthesis of Co3C carbide with carbon nanotubes

Nanoscaled (about 15 nm of size) metastable carbide Co3C was synthesized in a high-energy planetary ball mill by mechanical alloying of a mixture of powder cobalt (75 at. %) and multiwalled carbon nanotubes (CNT, 25 at. %). Phase transformation takes place at reaction milling according to the reaction hcp-Co + CNT ® Co3C (reaction time is 120 - 220 min). The crystal structure of the Co3C carbide formed in the milling products was studied by X-ray diffraction method. It has revealed that the Co3C phase crystallizes in a Fe3C-type structure with a = 0.4982(3) nm, b = 0.6715(6) nm, c = 0.4457(7) nm, Pnma space group. The reliability factor RB is equal to 0.065 for 48 reflections presented at diffraction pattern. It is found that the crystal structure of the Co3C carbide obtained by reaction milling of the Co-CNT charge is significantly internally deformed (distortion degree of the CCo6 octahedron is 3.67 %) and contains the reduced interatomic Co-C distances (up to 0.188 nm). It was shown that the use of carbon nanotubes instead of graphite substantially reduces the duration of the Co3C carbide synthesis.

The role of spin-orbit coupling in the photolysis of methylcobalamin.

The photolysis of the methylcobalamin cofactor (MeCbl) in its base-off form was investigated by considering the extent of spin-orbit coupling (SOC). Triplet Co-C photodissociation pathways previously invoked at the density functional theory level using Landau-Zener theory were further validated with ab initio calculations that combine SOC based on multi-state second order perturbation theory. It was determined that SOC is feasible between singlet and triplet states at elongated Co-C distances, leading to photodissociation from the state having dominant σ(dz(2)) character, by either direct coupling with the lowest singlet states or by crossing with SOC mixed triplets.

Testing colour discrimination models with free-flying bumblebees (Bombus terrestris L.): the unexpected effect of inspection time

Event Abstract Back to Event Testing colour discrimination models with free-flying bumblebees (Bombus terrestris L.): the unexpected effect of inspection time Francismeire J. Telles1* and Miguel A. Rodríguez-Gironés1 1 Estación Experimental de Zonas Áridas -EEZA, Departament of Functional and Evolutionary Ecology , Spain Several models have been proposed to explain how bees see and discriminate colours. To investigate the accuracy of two contending models, the colour hexagon and the colour opponent coding model (COC), we trained 64 bumblebees to discriminate between four colour pairs (16 bees per pair), having the same hexagon units (0.05) but differing in their COC distances (0.55-1.5 units). While the proportion of correct choices increased with COC distance, the effect was mediated by an increase in the time that bumblebees spent inspecting colours before choosing one, and the effect of COC distance on performance disappeared after statistically correcting for inspection time. Neither of the models could fully account for the data: the colour hexagon model cannot explain the relationship between COC distance and inspection time, and the COC model predicted that, after correcting for inspection time, performance should increase with COC distance. Figure 1 Acknowledgements Spanish National Research Council – CSIC and Estación Experimental de Zonas Áridas – EEZA. This work was supported by CGL2010-16795 References Backhaus, W. (1991). Color Opponent Coding in the Visual System of the Honeybee. Vision Res., 31(7), 1381–1397. Chittka, L. (1992). The colour hexagon: a chromaticity diagram based on photoreceptor excitations as a generalized representation of colour opponency. Journal of Comparative Physiology A, 170(5), 533–543. doi:10.1007/BF00199331 Keywords: Bumblebees, vision models, Colour discrimination, search time, Colour Hexagon Model, Colour Opponent Coding Model Conference: International Conference on Invertebrate Vision, Fjälkinge, Sweden, 1 Aug - 8 Aug, 2013. Presentation Type: Poster presentation preferred Topic: Colour and polarisation vision Citation: Telles FJ and Rodríguez-Gironés MA (2019). Testing colour discrimination models with free-flying bumblebees (Bombus terrestris L.): the unexpected effect of inspection time. Front. Physiol. Conference Abstract: International Conference on Invertebrate Vision. doi: 10.3389/conf.fphys.2013.25.00108 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Apr 2013; Published Online: 09 Dec 2019. * Correspondence: Miss. Francismeire J Telles, Estación Experimental de Zonas Áridas -EEZA, Departament of Functional and Evolutionary Ecology, Almería, Almería, 04120, Spain, meirecuesta@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Francismeire J Telles Miguel A Rodríguez-Gironés Google Francismeire J Telles Miguel A Rodríguez-Gironés Google Scholar Francismeire J Telles Miguel A Rodríguez-Gironés PubMed Francismeire J Telles Miguel A Rodríguez-Gironés Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

On the Importance of Ribose Orientation in the Substrate Activation of the Coenzyme B12‐Dependent Mutases

The degree to which the corrin ring portion of coenzyme B(12) can facilitate the H-atom-abstraction step in the glutamate mutase (GM)-catalyzed reaction of (S)-glutamate has been investigated with density functional theory. The crystal structure of GM identifies two possible orientations of the ribose portion of coenzyme B(12). In one orientation (A), the OH groups of the ribose extend away from the corrin ring, whereas in the other orientation (B) the OH groups, especially that involving O3', are instead directed towards the corrin ring. Our calculations identify a sizable stabilization amounting to about 30 kJ mol(-1) in the transition structure (TS) complex corresponding to orientation B (TS(B)CorIm). In the TS complex where the ribose instead is positioned in orientation A, no such effect is manifested. The observed stabilization in TS(B)CorIm appears to be the result of favorable interactions involving O3' and the corrin ring, including a C-HO hydrogen bond. We find that the degree of stabilization is not particularly sensitive to the Co-C distance. Our calculations show that any potential stabilization afforded to the H-atom-abstraction step by coenzyme B(12) is sensitive to the orientation of the ribose moiety.

Bis[1,3-bis(trimethylsilyl)allyl]cobalt(II), a stable electron-deficient allyl complex.

The title compound, bis[(1,2,3-η)-(2E)-1,3-bis(trimethylsilyl)-prop-2-enyl]cobalt(II), [Co(C 9 H 21 Si 2 ) 2 ], is a homoleptic allyl complex with η 3 -bound ligands. The Co-C distances range from 1.996 (3) to 2.096 (3) A and the allyl ligands adopt staggered, nearly parallel, arrangements around the Co atom. The trimethylsilyl groups are in syn-anti conformations; the steric shielding they provide to the metal is probably responsible for the thermal stability of the compound.

NMR Spectroscopic Characterization of Methylcobalt(III) Compounds with Classical Ligands. Crystal Structures of [Co(NH(3))(5)(CH(3))]S(2)O(6), trans-[Co(en)(2)(NH(3))(CH(3))]S(2)O(6) (en = 1,2-Ethanediamine), and [Co(NH(3))(6)]-mer,trans-[Co(NO(2))(3)(NH(3))(2)(CH(3))](2)-trans- [Co(NO(2))(4)(NH(3))(2)

A series of methylcobalt(III) compounds with solely classical ligands such as NH(3), H(2)O, NO(2)(-), CN(-), and 1,2-ethanediamine (en) has been prepared by ligand substitution of the pentaamminemethylcobalt(III) cation. The new compounds have been characterized by (1)H, (13)C, and (59)Co nuclear magnetic resonance spectroscopy and by absorption spectroscopy. Single-crystal X-ray structure determinations at 122.0(5) K were performed on [Co(NH(3))(5)(CH(3))]S(2)O(6) (1), trans-[Co(en)(2)(NH(3))(CH(3))]S(2)O(6) (2), and [Co(NH(3))(6)]-mer,trans-[Co(NO(2))(3)(NH(3))(2)(CH(3))](2)-trans-[Co(NO(2))(4)(NH(3))(2)] (3). Compound 1 is monoclinic, P2(1)/n, with cell dimensions a = 6.4856(9) Å, b = 18.0720(11) Å, c = 9.7854(14) Å, and beta = 98.280(13) degrees. Compound 2 is orthorhombic, P2(1)2(1)2, with cell dimensions a = 12.211(3) Å, b = 10.107(3) Å, and c = 11.514(3) Å. Compound 3 is monoclinic, P2(1)/n, with cell dimensions a = 8.390(2) Å, b = 8.970(3) Å, c = 20.650(9) Å, and beta = 91.29(2) degrees. Virtually identical Co-C distances in the range 1.980-1.984 Å are found in the three compounds. The methyl group exerts a strong trans influence. The largest relative elongation of the bond to the trans ligand is 0.170 Å in the trans-[Co(en)(2)(NH(3))(CH(3))](2+) cation. The structural trans influence appears to decrease with the overall charge of the coordination compound. Estimates of the scalar one-bond cobalt-carbon coupling constants, (1)J(Co)(-)(C), in the pentacyanomethylcobalt(III) anion was obtained by line shape analysis, yielding values of 127, 95, and 62 Hz for the cis cyano groups, the trans cyano group, and the methyl group, respectively.

Cobaltocenium bis[(4,5-dimercapto-S4,S5)-1,3-dithiole-2-thionato]nickelate

The coordination anions of the title compound [Co(C 5 H 5 ) 2 ][Ni(dmit) 2 ] are planar with a shuttleshaped D 2h configuration. The cobaltocenium cations take an eclipsed D 2h conformation with an average Co-C distance of 2.037 (16) A. The crystal consists of sheets of S...S connected anionic stacks with pairs of cations between them

Diolefinbis(trimethyIphosphine)cobalt(0) Compounds: Stable Organometallic Radicals with Distorted Ground State Structures

Abstract Diolefincobalt(O) complexes Co(L2)(PMe3)2 {L2 -[CH2 = CHSi(OMe)2]2O (1), [CH2 =CHSi(OEt)2]2O (2), (CH2 =CHCH2)2SiMe2 (3), [(CH2 =CHCH2)2N]2CH2 (4)} have been synthesized from Co(C5H8)(PMe3)3 and diolefins at ambient temperatures. Reactions with allyl ethers or with allyltin or allylphosphorus compounds involve transfer of allyl groups to the cobalt, while allylamine simply replaces cyclopentene (C5H8) to give Co(CH2 =CHCH2NH2)(PMe3)3 (5). Cationic cobalt(I) complexes containing olefin ligands as in 1-4 could not be obtained under conditions where norbornadiene readily gave [Co(C7H8)(PMe3)3 ]BF4 (6). Paramagnetic 4 shows a magnetic moment μeff = 2.0 μв (between 3.6 and 293 K), corresponding to one unpaired electron per cobalt atom. Compound 4 crystallizes in the space group P21/c with Z = 4, a = 14.986(4), b = 17.223(5), c = 15.436(3) Å,β = 117.98(2)°, V = 3518.4 Å3 . Each cobalt atom is η4-coordinated to a diolefin involving the smaller of two possible chelating rings. The Co-C distances range only from 2.029(6) to 2.058(6) Å for the olefin ligands, whereas Co-P bond lengths at each cobalt differ significantly: Co1-P1 2.188(2), Co1-P2 2.248(2); Co2-P3 2.185(2), Co2-P4 2.258(2) Å. This feature of two significantly different Co-L bond lengths is hitherto seen in all structurally characterized (bisolefin)CoL2 complexes (L = PMe3, CH3CN) and can be rationalized by molecular orbital calculations (Extended Hückel) on the 17 electron model system (PH3)2Co(C2H4)2.

The structure of (1,2:5, 6?-cyclononatetraene) (?-cyclopentadienyl)cobalt, CoC14H15

The title compound crystallizes in the monoclinic space groupP21/a,a=11.50(2),b=7.724(1),c=12.599(3) A,β=102.22(5)°,Z=4. The structure was solved by direct methods and refined by full-matrix least squares toR=0.049 for 1032 observed reflections. The cobalt atom is π-bonded to the cyclopentadienyl ring, with a mean Co-C distance of 2.07(1) A, and also π-bonded to the cyclonoatetraene ring at C(2)-C(3) and at C(6)-C(7), with a mean Co-C distance of 2.00(1) A.

Yttrium cobalt carbide (YCoC): a simple organometallic polymer in the solid state with strong cobalt-carbon .pi. bonding

Gerss and Jeitschko recently synthesized YCoC, which contains well-isolated infinite linear CoC/sup 3 -/ chains, marked by a short Co-C distance. The authors have examined the bonding in this polymer. It has substantial ..pi.. character, and that bonding could be strengthened by decreasing the electron count or oxidation. They think the chains should be magnetic.

Poly(tertiary phosphines and arsines). 18. Preparation and structure of bis{.mu.-[(methylamino)bis(dimethoxyphosphine)]}-bis(dicarbonylcobalt), a binuclear complex with approximate square-pyramidal and trigonal-bipyramidal coordination of cobalt atoms in the same molecule

The preparation and the X-ray crystal-structure analysis of bis)..mu..-((methylamino)bis-(dimethoxyphosphine)))-bis(dicabonylcobalt), a binuclear cobalt carbonyl complex containing the ligand CH/sub 3/N(P(OCH/sub 3/)/sub 2/)/sub 2/ is described. A single-crystal X-ray diffraction study of this complex shows a structure with a cobalt-cobalt bond 2.498 angstrom long bridged by two CH/sub 3/N(P(OCH/sub 3/)/sub 2/)/sub 2/ ligands. The two cobalt atoms are both five-coordinate and have identical sets of ligands, each of the two being bonded to the other cobalt atom, to two carbonyl groups, and to two trivalent phosphorus donors. However, the two cobalt atoms are not equivalent; one has trigonal-bipyramidal coordination and the other has square-pyramidal coordination. The trigonal-bipyramidal cobalt atom has the other cobalt atom and a carbonyl group in the axial position. The square-pyramidal cobalt atom has a carbonyl group in the apical position. The difference in coordination of the two cobalt atoms probably results from the packing of a fluxional molecule which has a symmetrical average structure in solution. Although the v(CO) frequencies in the infrared spectrum in solution all appear in the terminal region, the complex in the crystal contains a carbonyl group in a borderline semibridging position with Co-C distances of 1.756 and 2.812 angstrom, probably as the resultmore » of the crystal packing. The atoms of th Co/sub 2/(CO)/sub 4/ unit in the complex are essentially coplanar, and the least-squares best plane through these atoms is an approximate mirror plane for the molecule.« less

The structure of nonacarbonyl-μ3-methylidyne-triangulo-tricobalt. X-ray and neutron diffraction studies

The titlecompound, Co3(CO)9CH , crystallizes in space group P1 (Z = 2). The unit-cell dimensions determined from neutron diffraction data at 102 K are a = 7.936(2), b = 13.656(4), c = 6.856 (2).A, a = 101.60 (2), fl = 109.34 (2) and y = 93.96 (2) °. The structure was solved by Patterson methods with X-ray diffraction data obtained at room temperature, and further refined with low-temperature X-ray and neutron diffraction data. R(F) (neutron) = 0.037 for 3781 observations. The molecule possesses an idealized Cap point symmetry. Three Co(CO)a groups and a CH group form a distorted tetrahedron. The high resolution of the present study reveals significant differences between the axial and equatorial Co-C bond lengths, the average Co-C distances for these being respectively 1.837(2) and 1.798 (1)/~. The C-H bond distance as determined by neutron diffraction is 1.084 (1) ,/~. The Co neutron scattering length has been refined to a value of 2.48 (2) fm.

Stereochemistry of low-spin cobalt porphyrins. 9. preparation and characterization of five-coordinate organocobalt(III) derivatives

Organocobalt(III) derivatives have been prepared by direct aerial oxidation of tetraphenylporphinatocobalt(II) in solutions containing acetone, acetophenone, and malononitrile. The molecular and crystal structure of acetonyl-α, β, γ, δ-tetraphenylporphinatocobalt(III) has been determined by x-ray diffraction techniques. The porphinato core provides the base of a square pyramid, with the acetonyl group at the apex. CH 3C(O)CH 2CoTPP crystallizes in the triclinic system, space group P 1 . The unit cell has a = 12.187 (8) Å, b = 14.157 (5) Å, c = 11.925 (5) Å, α = 94.70 (2)°, β = 111.39 (4)°, and γ = 68.44 (4)°. The calculated and experimental densities are 1.356 and 1.34 g/cm 3 respectively for Z = 2, required crystal symmetry 1 . Final discrepancy indices are R 1 = 0.050 and R 2 = 0.076. The average Co-N distance is 1.948 Å and the Co-C distance is 2.028 Å.