Electrocatalytic hydrogen evolution by cobalt difluoroboryl-diglyoximate complexes

In the presence of moderately strong acids in CH3CN, cobalt complexes with BF2-bridged diglyoxime ligands are active catalysts for the reduction of protons to H2 at potentials as positive as -0.28 V vs. SCE.     

Electrocatalytic hydrogen evolution using triaryl corrole cobalt complex

Three cobalt triaryl corroles bearing an electron-withdrawing or electron-donating group at 10-meso-phenyl were synthesized and characterized. Two of them are new cobalt corroles prepared in this study. These cobalt corroles were characterized using high-resolution mass spectrometry, UV–Vis., nuclear magnetic resonance, X-ray photoelectron spectroscopy, and single-crystal X-ray structure determination. All synthesized cobalt corroles efficiently catalyzed the hydrogen evolution reaction (HER) in neutral aqueous media at an overpotential of 838 mV. The HER activity of these cobalt corroles significantly depended on the virtue of peripheral substituents.     

Electrocatalytic hydrogen evolution in acidic water with molecular cobalt tetraazamacrocycles

A series of water-soluble molecular cobalt complexes of tetraazamacrocyclic ligands are reported for the electrocatalytic production of H(2) from pH 2.2 aqueous solutions. The comparative data reported for this family of complexes shed light on their relative efficiencies for hydrogen evolution in water. Rotating disk electrode voltammetry data are presented for each of the complexes discussed, as are data concerning their respective pH-dependent electrocatalytic activity. In particular, two diimine-dioxime complexes were identified as exhibiting catalytic onset at comparatively low overpotentials relative to other reported homogeneous cobalt and nickel electrocatalysts in aqueous solution. These complexes are stable at pH 2.2 and produce hydrogen with high Faradaic efficiency in bulk electrolysis experiments over time intervals ranging from 2 to 24 h.     

Molybdenum-sulfur dimers as electrocatalysts for the production of hydrogen at low overpotentials

(CpMomu-S)2S2CH2, 2, and related derivatives serve as electrocatalysts for the reduction of protons with current efficiencies near 100%. The kinetics of the electrochemical reduction process has been studied, and the effects of varying the proton source, the solvent, the cyclopentadienyl substituents, and the sulfur substituents on the catalyst have been examined. The reduction of excess p-cyanoanilinium tetrafluoroborate under a hydrogen atmosphere in 0.3 M Et4NBF4/acetonitrile buffered at pH 7.6 is catalyzed by 2 at -0.64 V versus ferrocene, with an overpotential of 120 mV. Protonation of the sulfido ligand in 2 is an initial step in the catalytic process, and the rate-determining step at high acid concentrations appears to be the elimination of dihydrogen. The elimination may occur either from adjacent hydrosulfido sites or from a hydrosulfido-molybdenum hydride intermediate.     

Synthesis and spectral studies of a 12-membered tetraimine macrocyclic ligand and its complexes

[2 + 2] Condensation between 3,4-diaminobenzophenone and benzil in a 1:1 molar ratio in methanol at room temperature resulted in the formation of a novel Schiff base tetraimine macrocyclic ligand, (L): 5,6;11,12-dibenzophenone-2,3;8,9-tetraphenyl-1,4,7,10-tetraazacyclo-dodeca-1,3,7,9-tetraene. The macrocyclic complexes of the type, [FeLCl₂]Cl and [MLCl₂] [M = Co(II) and Cu(II)] have been prepared by reacting iron(III) chloride or metal(II) chlorides with the ligand, L in 1:1 molar ratio in methanol. The stoichiometry corresponding to the formation of the ligand framework, L was ascertained on the basis of results of elemental analyses,¹H-NMR and FAB-mass measurements while that of complexes were ascertained by results of elemental analyses and in solution by Job’s method. The mode of bonding and the geometry of the complexes have been confirmed on the basis of i.r., u.v.–vis spectral findings and magnetic susceptibility measurements which revealed an octahedral geometry for all the complexes. The nature of the complexes was confirmed by conductometric studies.     

Electrocatalytic reduction of organic halides with cobalt bipyridine complexes

The electrocatalytic reduction of organic halides by the [Nibpy]⁺complexes coordinationally unsaturated with bpy (at potentials of the first wave) and by the coordinationally saturated [Nibpy₂]^–complexes (at potentials of the second wave) was observed. The apparent rate constant of the process decreased with an increase in the difference of the reduction potentials of the substrate and catalyst in a large range of the driving force of the process.     

New glyoxime derivatives and their transition metal complexes

Two new vic-dioxime ligands and their complexes with Co⁺², Ni⁺², Cu⁺², Cd⁺², and Zn⁺² ions were synthesized. Primer amines (3,4-methylenedioxaaniline and 4-methylbenzylamine) reacted with antichloroglyoxime to give 3,4-methylenedioxaphenylaminoglyoxime (H₂L¹) and N-(4-methylbenzyl)aminoglyoxime (H₂L²) ligands. Structures of the ligands and their complexes are proposed based on elemental analyses, IR, UV-Vis, and ¹H NMR spectra, magnetic susceptibility measurements, and thermogravimetric analyses (TGA). The article was submitted by the authors in English.     

Isomeric distribution and catalyzed isomerization of cobalt(III) complexes with pentadentate macrocyclic ligands. importance of hydrogen bonding

We have investigated the isomeric distribution and rearrangement of complexes of the type [CoXLn]2+,3+ (where X = Cl-, OH-, H2O, and Ln represents a pentadentate 13-, 14-, and 15-membered tetra-aza or diaza-dithia (N4 or N2S2) macrocycle bearing a pendant primary amine). The preparative procedures for chloro complexes produced almost exclusively kinetically preferred cis isomers (where the pendant primary amine is cis to the chloro ligand) that can be separated by careful cation-exchange chromatography. For L13 and L14 the so-called cis-V isomer is isolated as the kinetic product, and for L15 the cis-VI form (an N-based diastereomer) is the preferred, while for the L14(S) complex both cis-V and trans-I forms are obtained. All these complexes rearrange to form stable trans isomers in which the pendent primary amine is trans to the monodentate aqua or hydroxo ligand, depending on pH and the workup procedure. In total 11 different complexes have been studied. From these, two different trans isomers of [CoClL14(S)]2+ have been characterized crystallographically for the first time in addition to a new structure of cis-V-[CoClL14(S)]2+; all were isolated as their chloride perchlorate salts. Two additional isomers have been identified and characterized by NMR as reaction intermediates. The remaining seven forms correspond to the complexes already known, produced in preparative procedures. The kinetic, thermal, and baric activation parameters for all the isomerization reactions have been determined and involve large activation enthalpies and positive volumes of activation. Activation entropies indicate a very important degree of hydrogen bonding in the reactivity of the complexes, confirmed by density functional theory studies on the stability of the different isomeric forms. The isomerization processes are not simple and even some unstable intermediates have been detected and characterized as part of the above-mentioned 11 forms of the complexes. A common reaction mechanism for the isomerization reactions has been proposed for all the complexes derived from the observed kinetic and solution behavior.     

X-ray photoelectron spectra of tetraaza macrocyclic complexes of cobalt with molecular oxygen

X-ray photoelectron spectroscopy has been used to determine the electronic state of the cobalt-molecular-oxygen fragment, the type of coordination, and, in some cases, the nature of the bond between the central ion and the axial ligand in the complexes [Co^II(htd)(NCS))C10₄, [-O₂{Co(htd((X)}₂](ClO₄)₂ (X=NCS^–, N₃ ^–, NCO^–, OH^–), and [O₂{Co(htd)(Im)}₂](ClO₄)₄. It has been established that the NCO^– and NCS^– ligands are coordinated as electron donors in an axial position by means of their nitrogen atoms. A conclusion regarding the electronic structure of the Co^III-O₂ ^2–-Co^III fragment has been drawn on the basis of an analysis of the binding energy (E_b) of the Co 2p_3/2 electrons in the oxygenated complexes and in the corresponding low-spin cobalt(II) compounds and cobalt(III) compounds.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 437–442, July–August, 1990.     

氮掺杂碳包埋钴纳米粒子电催化合成过氧化氢

电催化还原氧是一种新兴的可持续生产过氧化氢(H2O2)的合成技术,寻找低成本、高活性和高选择性的电催化剂是该技术实际应用的关键.钴氮掺杂的碳材料因含有钴氮(Co-Nx)催化活性位,成为一类新兴的可促进H2O2电化学合成的材料.本文采用低能耗干式球磨外加控制热解的方法来制备包含许多Co-Nx结构的钴氮掺杂碳材料.该方法使用材料廉价,即将醋酸钴、2-甲基咪唑和Ketjenblack EC-600JD高纯度且导电的碳黑分别作为金属、氮和碳的前体.在酸性介质中的电化学测试结果表明,该材料的氧还原反应电流密度明显增加,同时起始电位向正方向移动.该催化剂在较大电位范围内对H2O2的选择性约为90％.H2O2整体电解实验表明,H2O2产率达到100mmol gcat?1 h?1,H2O2法拉第效率达到85％(0.3Vvs.RHE条件下2h).耐久性测试(在0.3Vvs.RHE条件下6h)表明,催化剂表现出相对稳定的性能,且在整个测试循环中,法拉第效率达到约85％,表明催化剂在实际应用中具有良好的耐久性.催化剂表现出较高的电催化合成H2O2活性和选择性可能是由于形成了Co-Nx活性位,以及酸性环境和应用电位等其它因素的影响.     

氮掺杂碳包埋钴纳米粒子电催化合成过氧化氢

电催化还原氧是一种新兴的可持续生产过氧化氢(H2O2)的合成技术,寻找低成本、高活性和高选择性的电催化剂是该技术实际应用的关键.钴氮掺杂的碳材料因含有钴氮(Co-Nx)催化活性位,成为一类新兴的可促进H2O2电化学合成的材料.本文采用低能耗干式球磨外加控制热解的方法来制备包含许多Co-Nx结构的钴氮掺杂碳材料.该方法使用材料廉价,即将醋酸钴、2-甲基咪唑和Ketjenblack EC-600JD高纯度且导电的碳黑分别作为金属、氮和碳的前体.在酸性介质中的电化学测试结果表明,该材料的氧还原反应电流密度明显增加,同时起始电位向正方向移动.该催化剂在较大电位范围内对H2O2的选择性约为90％.H2O2整体电解实验表明,H2O2产率达到100mmol gcat?1 h?1,H2O2法拉第效率达到85％(0.3Vvs.RHE条件下2h).耐久性测试(在0.3Vvs.RHE条件下6h)表明,催化剂表现出相对稳定的性能,且在整个测试循环中,法拉第效率达到约85％,表明催化剂在实际应用中具有良好的耐久性.催化剂表现出较高的电催化合成H2O2活性和选择性可能是由于形成了Co-Nx活性位,以及酸性环境和应用电位等其它因素的影响.     

Photocatalytic activity of CdS nanocrystals stabilized by a polymer shell and promoted by cobalt and nickel complexes in the reaction of hydrogen evolution

Nanocrystals (NCs) of CdS with oleate surface (NC-1) and octadecyl thiolate surface (NC-2), stabilized by a polycation shell, were doped with nickel bis(2-aminobenzenethiolate) (1), cobalt(III) chlorobis(dimethylglyoximato)(2-mercaptopyridine) (2), and also with 1,2-ethanedithiol and didodecylsulfide clathrochelates of cobalt(II) (3 and 4). The influence of doping on the photocatalytic activity in the hydrogen evolution reaction was investigated. Complex 1 appeared to be the most effective cocatalyst for H₂ evolution with the reaction rate increased by the factor of 8—11. Accomodating the complex in a polymer shell yields the best result. The rate of H₂ evolution increases monotonically with increasing concentration of this complex until the concentration achieves the ratio of one complex molecule per single NC. It is shown that the chemical composition of the surface has a significant influence on their photocatalytic activity in the hydrogen evolution reaction. The activity of NC-2 is 200 times that of NC-1. The replacement of oleate groups of the latter with sulfide increases the activity of these photocatalysts by a factor of 2000.     

Catalytic hydrogen production at cobalt centres

The catalytic properties of a wide range of cobalt complexes with respect to proton reduction are discussed. Electrocatalytic as well as photocatalytic systems are addressed and to allow comparison between the different systems reported considerable attention is paid to the reaction conditions used. For the photocatalytic proton reduction a range of ruthenium, iridium and rhenium complexes are discussed as potential photosensitizers. The photocatalytic systems are discussed in detail and issues such as the nature of the sacrificial agent and the solvents used. Both intermolecular and intramolecular photocatalysis are considered. The results obtained are considered with respect to the need to the development of sustainable energy sources.     

Divalent nickel,cobalt and copper complexes of a tetradentate N6 macrocyclic ligand

Summary Divalent nickel, cobalt and copper salts react with 2,6-diaminopyridine and acetylacetone to form complexes containing a 16-membered N₆ tetradentate macrocyclic ligand. The complexes are characterised as distorted octahedra of the M(TML)X₂ type where M=nickel(II), cobalt(II) and copper(II); TML=tetradentate macrocyclic ligand and X=Cl, Br, NO₃ or NCS. The ligand coordinates through all the four azomethine nitrogen atoms which are bridged by acetylacetone moieties. Pyridine nitrogen does not participate in coordination, a fact supported by far i.r. studies. The magnetic, electronic and i.r. spectral studies indicate that the complexes have lower symmetries and the amounts of distortion calculated in terms of DT/DQ applying normalised spherical harmonic Hamiltonian theory indicate that these complexes are moderately distored.     

X-ray electronic spectra of certain tetraaza macrocyclic complexes of cobalt (III)

The electronic structure-Of several tetraaza macrocyclic complexes of cobalt (III), containing different axial acido ligands was studied using X-ray electron spectroscopy. The bond energies of electrons of nitrogen, cobalt, chlorine, bromide, and sulfur atoms were measured. It was shown that the bond energy of isoelectrons of the macrocyclic ligand nitrogen atoms is not a constant value, but depends on the nature of the additionally coordinated axial ligand, which reflects the cis-effect of the ligands in the macrocyclic complexes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 4, pp. 497–500, July–August, 1985.