Reverse-phase chromatographic separation of Co(II) and Co(III) as the Co(DEDTC)3 and Co(acac)3 complexes

A reverse-phase chromatographic method is described for the simultaneous determination of Co(II) and Co(III) using gradient elution of the Co(DEDTC)₃ and Co(acac)₃ complexes, respectively, with phosphate buffered acetonitrile water mixtures. The separated Co species are detected spectrophotometrically at 322?nm. The analytical range of the method is 0.1 to 1.25?μg/ml for Co(II) and 0.1 to 1.5?μg/ml for Co(III).     

Co(II) and Co(III) complexes of m-benziphthalocyanine

The syntheses and structural elucidations of three different cobalt complexes of m-benziphthalocyanine are reported; both Co(II) and Co(III) complexes can be generated, and the ring undergoes partial oxidation upon metalation with Co(OAc)2x4H2O.     

A study on Cu2Co2SOD and Co2Co2SOD by voltammetry and thin-layer spectroelectrochemistry

The electrochemistry of Co(2)Co(2)SOD and Cu(2)Co(2)SOD on a pyrolytic graphite electrode (PGE) without using mediators was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The reversible and quasi-reversible voltammetric responses were observed for Co(2)Co(2)SOD and Cu(2)Co(2)SOD, respectively. Their formal redox potentials and electron numbers involved in electrode reactions were obtained, and are in agreement with those by spectroelectrochemistry (SEC).     

Basic metals IV. The synthesis of monocyclopentadienylcobalt complexes containing CoZn,CoCu,CoSn and CoHg bonds

The pronounced Lewis basic character of the metal atom in C₅H₅Co(PMe₃)₂ is demonstrated by its reactions with ZnCl₂/PMe₃, [(PMe₃)₂CuCl]₂, SnCl₄, R₃SnCl (R  Me, Ph) and HgCl₂ which lead to stable monocyclopentadienylcobalt complexes containing CoZn, CoCu, CoSn and CoHg bonds.     

The crystal structures of Co3Se4 and Co7Se8

The crystal structures of Co₃Se₄ and Co_6.8Se₈ have been refined from twinned single crystal and powder X-ray diffraction data. The refined structures are isostructural to the Cr_3±xSe₄ and Cr₇Se₈ types, respectively. The structures are described as superstructures of the Cd(OH)₂-type structure, where the empty layers of unoccupied octahedra are replaced with alternating Co filled and empty [100] rods and Co filled Kagomè nets for Co₃Se₄ and Co_6.8Se₈, respectively. The structure of Co₃Se₄ is not a substructure of Co₇Se₈ and the path from Co₇Se₈ to Co₃Se₄ by removing 1/4 of the Co atoms in the Kagomè nets involves both gain and loss of symmetry. Yet the refinements of Co_6.8Se₈ suggest an extended homogeneity field.     

Phenolate and phenoxyl radical complexes of Co(II) and Co(III)

The new phenol-imidazole pro-ligands (R)LH react with Co(BF(4))(2).6H(2)O in the presence of Et(3)N to form the corresponding [Co(II)((R)L)(2)] compound (R = Ph (1), PhOMe (2), or Bz (3)). Also, (Bz)LH, reacts with Co(ii) in the presence of Et(3)N and H(2)O(2) to form [Co(III)((Bz)L)(3)](4). The structures of 1.2.5MeCN, 2.2DMF, 3.4MeOH, and 4.4DMF have been determined by X-ray crystallography. 1, 2, and 3 each involve Co(II) bound to two N,O-bidentate ligands with a distorted tetrahedral coordination sphere; 4 involves Co(III) bound to three N,O-bidentate ligands in a mer-N(3)O(3) distorted octahedral geometry. [Co(II)((R)L)(2)](R = Ph or PhOMe) undergo two, one-electron, oxidations. The products of the first oxidation, [1](+) and [2](+), have been synthesised by the chemical oxidation of 1 and 2, respectively; these cations, formulated as [Co(II)((R)L*)((R)L)(2)](+), comprise one phenoxyl radical and one phenolate ligand bound to Co(II) and are the first phenoxyl radical ligand complexes of tetra-coordinated Co(II). 4 undergoes two, one-electron, ligand-based oxidations, the first of which produces [4](+), [Co(III)((Bz)L*)((Bz)L)(2)](+). Unlike [1](+) and [2](+), product of the one-electron oxidation of [Co(II)((Bz)L)(2)], [3](+), is unstable and decomposes to produce [4](+). These studies have demonstrated that the chemical properties of [M(II)((R)L*)((R)L)(2)](+)(M = Co, Cu, Zn) are highly dependent on the nature of both the ligand and the metal centre.     

Co(II) and Co(III) macrocyclic boron-bearing dioximates

Syntheses are reported for CoD₃(BF)₂ and [CoD₃(BF)₂]BF₄,where H ₂ D is dimethylglyoxime, -benzyldioxime, or cyclohexanedione dioxime. The IR spectra at 400–4000 cm ^–1 have been measured, as have the electronic absorption spectra and the¹H,¹³C,and ¹¹BNMR spectra; a comparison is made with the spectra of the analogous iron(II) complexes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 3, pp. 375–377, May–June, 1990.     

Partial Synthesis of CoαCoβ-Dicyano-176-Norcobinamide

Summary. Recent interest in norvitamin B₁₂-derivatives, homologues of complete vitamin B₁₂-derivatives, lacking the methyl group at carbon 176, stems from the identification of the corrinoid cofactor of the tetrachloroethene reductive dehalogenase of Sulfurospirillum multivorans as 176-nor-pseudovitamin B₁₂. Here we report the partial synthesis of the corrinoid Co_αCo_β-dicyano-176-norcobinamide by condensation of cobyric acid and 2-aminoethanol. In addition, the partial synthesis of crystalline Co_α-aquo-Co_β-cyanocobyric acid by acid catalyzed hydrolysis of vitamin B₁₂ is detailed, improving the method and the isolation procedure worked out earlier by Bernhauer et al. The solution structure of Co_αCo_β-dicyano-176-norcobinamide was studied by spectroscopy and was compared with that of the homologue Co_αCo_β-dicyanocobinamide. The title compound, Co_αCo_β-dicyano-176-norcobinamide, represents the dicyano-form of a potential biosynthetic precursor of the 176-nor-B₁₂-derivatives, such as 176-nor-pseudovitamin B₁₂.     

Co_4~Ⅲ四边形和Co~Ⅱ八面体构筑块搭建的一维超分子化合物

在水热条件下,以4,5-咪唑二羧酸作为有机配体,1,10-邻菲咯啉作为端基配体,硝酸钴作为金属源,合成了一维超分子化合物[Co5(C5N2O4H)4(C5N2O4H3)2(C12N2H8)4(H2O)2]·(H2O)6(1)。单晶X-射线衍射分析结果表明,化合物1属于三斜晶系,P1空间群,Mr=2082.09,a=13.104(3),b=13.463(3),c=13.708(3),α=75.03(3)°,β=70.00(3)°,γ=65.39(3)°,V=2046.9(10)3。在化合物1中,CoⅢ4四边形构筑块与CoⅡ八面体构筑块之间通过氢键作用相互连接,沿[111]方向形成一条无限延伸的超分子链。此外,通过粉末X-射线衍射、热重分析、红外光谱和元素分析对化合物1进行了相关表征。     

Interaction of Co+ and Co2+ with glycine. A theoretical study

Cobalt cations are open shell systems with several possible electronic states arising from the different occupations of the 3d and 4s orbitals. The influence of these occupations on the relative stability of the coordination modes of the metal cation to glycine has been studied by means of theoretical methods. The structure and vibrational frequencies have been determined using the B3LYP method. Single-point calculations have also been carried out at the CCSD(T) level. The most stable structure of Co(+)-glycine is bidentate, with the Co(+) cation interacting with the amino group and the carbonyl oxygen of neutral glycine, and the ground electronic state being (3)A. For Co(2+)-glycine, the lowest energy structure corresponds to the interaction of the metal cation with the carboxylate group of the zwitterionic glycine, the ground electronic state being (4)A'.     

Dinuclear Co(III)/Co(III) and Co(II)/Co(III) mixed-valent complexes: synthetic control of the cobalt oxidation level

The reactivity of cobalt(II) salts towards H(3)L (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) was studied in different reaction conditions. Accordingly, the interaction of cobalt(II) acetate with H(3)L in methanol gives rise to the discrete complex [Co(III)(2)L(OAc)(2)(OMe)]*1.5H(2)O.MeOH, 1. Reaction of cobalt(II) acetylacetonate with H(3)L in the presence of dicarboxylic acids was also investigated. Thus, when cobalt(II) acetylacetonate and H(3)L are mixed with terephthalic or malonic acid in 4 : 2 : 1 molar ratios, the mixed valent [Co(II/III)(2)L(acac)(p-O(2)CC(6)H(4)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*2H(2)O*2MeOH, 2 and [Co(II/III)(2)L(acac)(O(2)CCH(2)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*7H(2)O, complexes are isolated. Decreasing the pH of the medium, by addition of a second mol of dicarboxylic acid, leads to [Co(II/III)(2)L(O(2)CCH(2)CO(2))(MeOH)]*2MeOH, 4, while the reaction with terephthalic acid does not proceed. 1, 2 and 4 were crystallographically characterised and all the complexes are dinuclear, with hydrogen bonds that expand the initial nodes. The magnetic characterisation, as well as the NMR spectroscopy, indicates a diamagnetic nature for 1, in agreement with the presence of Co(III), showing the aerial oxidation suffered by the cobalt(II) ions. Nevertheless, are paramagnetic. Temperature variable magnetic measurements were recorded for the crystallographically characterised complexes 2 and 4 and these studies confirm the mixed valence Co(II)/Co(III) nature of the compounds. The best fits of the magnetic data give an axial distortion parameter Delta = 628.7 cm(-1) for 2 and 698.8 cm(-1) for 4, and spin-orbit coupling constant lambda = -117.8 cm(-1) for 2 and -107.0 cm(-1) for 4. Therefore, this study shows that the oxidation degree of the initial cobalt(ii) salt by atmospheric oxygen can be controlled according to the pH of the medium.     

Co(Ⅲ)(Salen)催化的外消旋环氧化合物不对称开环

用较易得到的(R,R)-1,2-二苯基乙二胺(DPEDA)与-2-羟基-5-甲基-3-叔丁基苯甲醛缩合,得到手性Salen,再与Co络合,氧化后得到Salen型手性催化剂(R,R)-2。(R,R)-2可催化外消旋环氧化物的动力学水解拆分,所得手性二醇和手性环氧化合物对映体过量最高分别可达99%和92%。     

Kinetics and Mechanism of Co Substitution by Phosphites of Co4(CO)12

Abstract

The otherwise very fast CO substitution of Co₄(CO)₁₂ by P(OMe)₃ and P(OEt)₃ in aprotic solvents, affording phosphite-monosubstituted products was retarded by the use of CHCI₃ as solvent. This made it possible to investigate these reactions by conventional methods. Kinetic data were obtained by following changes in IR spectra during reaction. The rates show predominantly a ligand-dependent pathway, with the usual two-term rate law, rate = (k₁ + k₂ [P(OR)₃])C₄(CO)₁₂. It is suggested that the rates are retarded in protonic solvents by decreasing the nucleophilicity of phosphites due to a hydrogen bonding interaction between the H atom of CHCI₃ and the O atoms of the ligands.     

Co/HZSM-5催化剂中Co相态和价态的表征

苯乙烯是一种重要的化工原料 ,是合成聚苯乙烯等高分子材料的单体 .目前 ,工业上苯乙烯的生产采用两步法工艺 ,即苯和乙烯在 Al Cl3或 HZSM- 5催化剂上烷基化合成乙苯 ,然后乙苯再在含有助催化剂的氧化铁系催化剂上脱氢得到苯乙烯 .在另一部分工作中 ,我们采用金属负载 HZSM- 5分子筛催化剂研究了苯和乙烯一步合成苯乙烯反应 ,结果表明 ,Co/HZSM- 5是较好的催化剂[1] ,并提出了反应是经过中间物乙苯脱氢生成苯乙烯的机理 [2 ] .实验还发现 ,催化剂的焙烧和还原温度对苯乙烯的收率有很大影响 .本工作结合 XRD,TPR和 DRS等方法对 Co…     

Dinuclear Co(II)Co(III) mixed-valence and Co(III)Co(III) complexes with N- and O-donor ligands: characterization and water oxidation studies

The tridentate ligand N-methyl-N,N-bis(2-pyridylmethyl)amine (L) has been employed to synthesize a dinuclear Co(II)Co(III) mixed-valence complex containing μ-methoxo and μ-carboxylato bridging ligands, [LCo(II)(μ-carboxylato)bis(μ-methoxo)Co(III)L](ClO(4))(2). In this complex, the two pseudo-octahedral Co centers have an identical ligand environment, yet the average Co-N and Co-O bond distances at the two Co ions differ significantly. Electrochemical, spectroscopic, and magnetic susceptibility measurements confirm that it belongs to a localized Class II mixed-valence system, despite the presence of a short Co···Co distance of 3.021 ?. Oxidation of this Co(II)Co(III) complex leads to formation of the corresponding Co(III)Co(III) complex that was characterized structurally and spectroscopically. In addition, dinuclear and trinuclear μ-hydroxo Co(III) complexes have been obtained in the presence of phosphate anions and absence of methanol, respectively, suggesting that an additional bridging ligand is needed to stabilize the Co(III)bis(μ-hydroxo)Co(III) fragment. Moreover, the ability of the mixed-valence Co(II)Co(III) complex and the three related Co(III) complexes to electrocatalytically oxidize water was also investigated. The observed limited water oxidation catalytic ability for these systems suggests that a multinuclear Co cluster and/or presence of O-rich ligands may be needed for the generation of efficient molecular Co-based water oxidation catalysts.     

Co/HMS和Co/SiO2催化剂的表征及在费-托合成反应中的催化性能

 HMS介孔分子筛经水热处理得到无定形SiO2,分别以无定形SiO2和HMS为载体,用浸渍法制得了15%Co/SiO2和15%Co/HMS催化剂. 研究表明: 氧化态Co/SiO2和Co/HMS催化剂中的钴物种以Co3O4形式存在,且Co3O4晶粒粒径均较相应催化剂的孔径大,故有部分钴物种存在于催化剂外表面; 氧化态Co/HMS催化剂中的钴物种堵塞孔道较为严重; Co/HMS催化剂中存在较强的金属-载体相互作用,因此Co/HMS催化剂较Co/SiO2催化剂难还原; Co/HMS催化剂还原后具有较高的钴分散度,使其具有优异的费-托合成反应性能.     

Thermodynamic properties of Co3O4 and Sr6Co5O15 from first-principles

The Gibbs energy function of Sr(6)Co(5)O(15) is calculated by first-principles for use in CALPHAD thermodynamic modeling. An efficient method is employed, using the Debye-Gru?neisen model to predict the temperature dependence of the heat capacity and entropy. The equation of state from first-principles and the Debye temperature from harmonic phonon calculations by the supercell approach are taken as input. The effect of using the GGA+U approach on the results is also reported. The properties of Co(3)O(4) are predicted with this method to compare to experiments and quasi-harmonic phonon calculations and are shown to achieve the accuracy necessary for CALPHAD modeling.     

Studies of the hydrogen evolution reaction on smooth Co and electrodeposited Ni–Co ultramicroelectrodes

The hydrogen evolution reaction (HER) was studied on smooth Co and on electrodeposited Ni–Co ultramicroelectrodes (UMEs) in alkaline solutions at several temperatures by steady-state polarisation curves. The real electrochemical area was previously estimated by cyclic voltammetry to account for the large difference in roughness factor of the two surfaces. The values obtained for the Tafel slopes were very close to 2.303RT/βnF while the ‘apparent’ energies of activation were 59 and 41 kJ mol⁻¹ for Co and Ni–Co, respectively. A common Volmer–Heyrovsky mechanism with Heyrovsky as the rate-determining step (RDS) was initially proposed. This was confirmed when the experimental results were mathematically treated by a non-linear fitting procedure using the kinetic equations derived for that mechanism. The calculations revealed that Ni–Co is a more efficient catalyst for the HER then pure Co, with a rate constant value of 0.16×10⁻¹⁰ mol s⁻¹ cm⁻² at 25°C for the slow step. Although this value is more than one order of magnitude smaller than that already reported for deposited Ni, it is considerably larger than the one measured here (0.02×10⁻¹⁰ mol s⁻¹ cm⁻²) for pure Co at 25°C.