Double-Layer Effects in the Electroreduction of Cobalt(III) Trioxalate Complexes to Cobalt(0) Atoms on a Dropping Mercury Electrode

A polarographic investigation of solutions containing trioxalate complexes of Co(III) reveals that the overall electrode process Co(III) Co(0) is accompanied by slow formation of ionic associates between aquacomplexes of Co(II) and trioxalate complexes of Co(III). Use of a relatively high concentration of oxalate ions (0.001 M) quells this association. Under these conditions, it is possible to divide the measured current into two constituents related to the primary electroreduction Co(III) Co(II) and the subsequent process Co(II) Co(0). The earlier data on the rate constant and apparent transfer coefficient for the process Co(II) Co(0) are used for calculating corrected Tafel plots for the electrode reaction Co(III) Co(II). The plots are practically linear and independent of the concentration of the supporting-electrolyte cation in a wide range of potential drops (1 V) across the dense layer. A theoretically expected parallel shift of the plots is observed in solutions with a variable concentration of discharging species. This observation and similar data obtained for a mixed potassium–sodium supporting electrolyte bear testimony to good agreement between the obtained results and the theory.     

Sulfitoamine Complexes of Cobalt(III)

Abstract

Monosulfito and bis(hydrogensulfito) cobalt(III) complexes were prepared using sodium sulfite and sodium metabisulfite salts respectively. The two types of products showed different and characterizing patterns of IR and UV-visible spectra. They both contain Co-SO₃ linkages and the sulfite groups have similar or different site symmetries in the same compound.     

Kinetics and Mechanism of Electroreduction of Ammonia Complexes of Cobalt(II) on a Dropping Mercury Electrode

Effects of concentrations of ammonia (0.3–5.8 M) and supporting electrolytes (NaF, NaClO₄; 0.1–0.5 M) on the kinetics of electroreduction of ammonia complexes of cobalt(II) at a dropping mercury electrode are studied. Most experiments are performed with low concentrations of cobalt(II) complexes (1 × 10^–5 to 2 × 10^–5 M) in the absence of a polarographic maximum. The dependence of the half-wave potential of the reversible cathodic wave pertaining to the reduction of ammonia complexes of cobalt(II) on the concentration of ammonia molecules is obtained. It is found from the dependence that, at ammonia concentrations of 0.5–2.6 M, the slow electrochemical stage involves predominantly complexes Co(NH₃)₂ ²⁺. At higher ammonia concentrations, the stage involves complexes Co(NH₃) _k ²⁺ (k > 2), which form in preceding chemical stages from complexes Co(NH₃) _i ²⁺ (i = 3–6) that are predominant in solution. Values of the diffusion coefficients for complexes Co(NH₃) _i ²⁺, apparent transfer coefficients, and rate constant of the process of electroreduction of ammonia complexes of cobalt(II) are determined. The reasons for the complicating effect the insoluble products of reduction of cobalt(II) complexes have on the shape of polarographic waves are discussed.     

Cobalt(III) Complexes of D‐Galactosylamine

The β‐pyranose isomer of D ‐galactosylamine ( 1 ) formed complexes with three different cobalt(III) fragments. Crystals containing the dication [Co(tren)(β‐D ‐Galp1N2H_–1‐κ²N¹,O²)]²⁺ ( 3 ) showed coordination through the anomeric amino group (N1) and the deprotonated hydroxy group (O2) of the ⁴C₁ β‐pyranose form, which is also the major isomer of free galactosylamine. The cationic complexes [Co(fac‐dien)(β‐D ‐Galp1N2H_–1‐κ²N¹,O²)]²⁺ ( 4 ) and [Co(phen)₂(β‐D ‐Galp1N2H_–1‐κ²N¹,O²)]²⁺ ( 5 ) were analysed by NMR spectroscopy and showed the same coordination mode as 3 . In terms of available ligand isomers it was shown that 1 exhibits an anomeric equilibrium in solution of both pyranose and both furanose forms as is typical for the parent glycose, galactose.     

Electroreduction of Ru(III) Oxalate Complexes on DME at Variable Supporting-Electrolyte Concentration

The recharging of Ru(III) oxalate complexes is studied on DME in mixed sulfate–oxalate electrolytes of variable concentration. The discovered deceleration of the process with decreasing supporting-electrolyte concentration qualitatively agrees with the expected effect of the EDL structure on the recharging kinetics, but the obtained quantitative data are at severe variance with theory. At low supporting-electrolyte concentrations the process rate in freshly-prepared solutions depends on the concentration of oxalate ions. The dependence has nothing to do with trioxalate complexes of Ru(III) coexisting in the bulk solution with Ru(III) complexes, which have a reduced number of coordinated ligands, as such complexes emerge only after 2–3 days of storing the solutions. The most probable factor responsible for such a dependence seems to be a volume reaction of charge transfer from the formed Ru(II) complexes onto trioxalate complexes of Ru(III). The reaction has a catalytic effect on the hydration of the latter and seems to be responsible for the discrepancy between experiment and theory.     

Formation and Crystal Structure of Stable Five‐coordinate Diorgano Cobalt(III) Complexes

The mer‐octahedral complexes(2‐carbonyl)(4‐Me)(6‐tBu)phenolato[C,O]hydridotris(trimethylphosphine)cobalt(III) ( 1 ) or ‐(1‐carbonyl)(2‐oxo)(1,2‐diphenylethene)[C,O]hydridotris(trimethylphosphine)cobalt(III) ( 2 ) via formal insertion of propynoic acid ethyl ester into Co‐H functions afford pentacoordinate vinylcobalt(III) 3 and 4 , respectively, that are diamagnetic and attain a square pyramidal structure as exemplified by an X‐ray diffraction analysis of 3 .     

Dinuclear Cobalt(III) Complexes Showing a Co2O2 Metallacycle

The heptadentate Schiff base H₃L reacts with cobalt(II) acetate in methanol to form the discrete dinuclear complex Co₂L(OAc)₂(OMe)(H₂O)₂ ( 1 ·2H₂O). The reaction of 1 ·2H₂O with NMe₄OH·5H₂O in methanol gives rise to displacement of the acetate by methanolate groups, yielding Co₂L(OMe)₃(H₂O) ( 2 ·1H₂O). Recrystallizations of the Schiff base, 1 ·2H₂O and 2 ·H₂O in different solvents, produce single crystals of H₃L, 1 ·2.5H₂O and 2 ·2MeOH, respectively. The crystal structures of 1 ·2.5H₂O and 2 ·2MeOH show the cobalt atoms double bridged by and endogenous phenol oxygen atom and an exogenous methanolate oxygen donor, giving rise to Co₂O₂ cores with Co···Co distances of ca. 2.87 Å.     

咪唑钴(III)配合物还原动力学机理研究

配合物间的电子转移反应是近代化学中重要的一类反应［‘，’J，对于大多数反应来说，由于前驱配合物离子对形成常数较小，难以独立分离出各基元步骤动力学参数问；给研究带来困难问．为了丰富电子转移反应研究内容，寻找更多可供详细研究的反应体系，在前文报导［Fe（CN）6p还原高位阻［Co（tmen）3p”的反应动力学研究基础上＊，本文进一步合成了含有生物体系中常见配体咪哩（IInll）的Co仰）配合物［Co（NH。）。（ImH）］（CIO小和t，an。－［Co（NH。）（en）。（IInH）］（C104）。，再以［Fe（CN）6p为还原剂，考察了两C…     

Partial Molar Volumes of Cobalt(III) Complexes. Part 3: Homologous Series of Aminopentaamminecobalt(III) Complexes

Partial molar volumes (V ₂°) have been determined at infinite dilution in aqueous solution at 20 °C for a series of octahedral N₆-coordinated cobalt(III) species having five-coordinated ammonia ligands along with an N-coordinated linear alkyl amine whose alkyl chain was varied from ethylamine to octylamine. The experimental values for V ₂° are consistent with the relative sizes of the ligands but show increasing deviations from those predicted by computer modeling, as the size of the cation increases, presumably due to the void space of the cation that increases with the size of the amine ligand. The value of the partial molar volume at infinite dilution increased by about 16 mL⋅mol⁻¹ with each added methylene group.     

Heteroligand Cobalt(III) Complexes with Triethanolamine and Aminoacetic Acid

Heteroligand cobalt(III) chelates with triethanolamine and glycine, [Co(HTetm)GlyH₂O] · 2H₂O (I) and [Co(HTetm)GlyNH₃] · 2H₂O (II) (H₃Tetm is N(C₂H₄OH)₃ and HGly is glycine), were synthesized. The acidity constants of complex I were determined at an ionic strength of 0.1. The reactions of I with alcoholic solutions of acids, ammonia, and ammonium nitrate were studied. Binuclear complexes were obtained upon the interaction of I and II with CoCl₂ · 6H₂O. The complexes were characterized using UV–VIS (in aqueous and alcoholic solutions) and IR (in the solid state) spectroscopy. The ¹³C NMR spectra of solutions of Iand II were recorded. The plausible structures of the complexes are discussed.     

Formation and transformation of Amminecarbonatocobalt(III) Complexes

The preparation is described of [CoCO₃(NH₃)₅]ClO₄ · H₂O, trans-[CoCO₃(NH₃)₄(¹⁵NH₃)]ClO₄, and trans-[CoCO₃(NH₃)₄(NH₂CH₃)]ClO₄. The transformation reactions of these complexes, in which a chelate carbonate ligand is formed and one NH₃ is eliminated, were studied in solution and in the solid state. ¹H NMR spectroscopy is used for the identification of the products. It is shown that the transformation reactions are not stereospecific.     

Electroreduction of Oxalate Complexes of Ruthenium(III) on a Dropping Mercury Electrode: Effect of Alkali Metal Cations and Solution Acidity

It is established that the reaction of recharging trioxalate complexes of ruthenium(III) occurs in the case of solutions with excess supporting oxalate salts of alkali metals K⁺, Na⁺, and Cs⁺ in reversible conditions, and limiting recharge currents are caused by diffusion. At the same time, values of diffusion coefficients for complex anion [Ru(C₂O₄)₃]^–3 decrease by almost two times upon going from potassium to sodium and cesium electrolytes. Substantial differences in the limiting currents in solutions containing excess amounts of the above salts are explained by the formation, at least in the case of cesium and sodium electrolytes, of ionic associates whose reduction rate at a fixed potential is lower than that of nonassociated anion [Ru(C₂O₄)₃]^–3. With solution dilution by supporting salts, transition is observed from reversible recharge conditions to absolutely irreversible conditions and a change in the above sequence of the effect of supporting cations on the recharge rate; at a fixed potential, the process decelerates in the series Cs⁺ > K⁺ > Na⁺. The reduction wave of the ruthenium(II) oxalate complexes in solutions with excess supporting electrolyte happens to depend on pH and, probably, is determined by simultaneous formation of adsorbed atoms of hydrogen (or ruthenium hydride) on atoms of ruthenium(0).     

Electroreduction of CO2 to Formate with Low Overpotential using Cobalt Pyridine Thiolate Complexes

Electrocatalytic CO₂ reduction to value-added products provides a viable alternative to the use of carbon sources derived from fossil fuels. Carrying out these transformations at reasonable energetic costs, for example, with low overpotential, remains a challenge. Molecular catalysts allow fine control of activity and selectivity via tuning of their coordination sphere and ligand set. Herein we investigate a series of cobalt(III) pyridine-thiolate complexes as electrocatalysts for CO₂ reduction. The effect of the ligands and proton sources on activity was examined. We identified bipyridine bis(2-pyridinethiolato) cobalt(III) hexaflurophosphate as a highly selective catalyst for formate production operating at a low overpotential of 110 mV with a turnover frequency (TOF) of 10 s⁻¹. Electrokinetic analysis coupled with density functional theory (DFT) computations established the mechanistic pathway, highlighting the role of metal hydride intermediates. The catalysts deactivate via the formation of stable cobalt carbonyl complexes, but the active species could be regenerated upon oxidation and release of coordinated CO ligands.     

Features of Cobalt(II) Complexes Formation with Pharmacophore-Modified Apple Pectin

Russian Journal of General Chemistry - Complexation of cobalt(II) chloride with apple pectin modified with organic pharmacophores (nicotinic, salicylic, 5-aminosalicylic, or anthranilic acid) has...     

Nontoxic Cobalt(III) Schiff Base Complexes with Broad-Spectrum Antifungal Activity

Resistance to currently available antifungal drugs has quietly been on the rise but overshadowed by the alarming spread of antibacterial resistance. There is a striking lack of attention to the threat of drug-resistant fungal infections, with only a handful of new drugs currently in development. Given that metal complexes have proven to be useful new chemotypes in the fight against diseases such as cancer, malaria, and bacterial infections, it is reasonable to explore their possible utility in treating fungal infections. Herein we report a series of cobalt(III) Schiff base complexes with broad-spectrum antifungal activity. Some of these complexes show minimum inhibitory concentrations (MIC) in the low micro- to nanomolar range against a series of Candida and Cryptococcus yeasts. Additionally, we demonstrate that these compounds show no cytotoxicity against both bacterial and human cells. Finally, we report the first in vivo toxicity data on these compounds in Galleria mellonella, showing that doses as high as 266 mg kg⁻¹ are tolerated without adverse effects, paving the way for further in vivo studies of these complexes.     

Partial Molar Volumes and Refractions of Cobalt(III) Complexes, Part 1: Homologous Series of Hexaaminecobalt(III) Complexes

Both the partial molar volumes (V∘_solute) and refractions (R∘_solute) of the solute at infinite dilution have been determined for a series of four octahedral N₆-coordinated cobalt(III) species with increasing ligand size (ammonia, ethylenediamine, sepulchrate, and 1,2-diaminocyclohexane). The experimental values for V∘ _solute are consistent with the relative sizes of the ligands but show larger values than those generated by computer modeling as the size of the cation increases. This suggests that the void space of the cation increases with the size of the cation. It is proposed that increasing hydrophobicity of the alkane ligand frameworks contributes to larger volumes.     

Partial Molar Volumes and Refractions of Cobalt(III) Complexes, Part 2: Homologous Series of Nitrilopentaamminecobalt(III) Complexes

Both the partial molar volumes (V° _2m refractions (R° _2m ) of the solutes at infinite dilution have been determined at 20 °C for a series of six octahedral N₆-coordinated cobalt(III) species featuring five coordinated ammonia ligands along with a sixth N-coordinated organonitrile of increasing ligand size (from acetonitrile to sebaconitrile). The experimental values for V° _2m are consistent with the relative sizes of the ligands but show larger values than those generated by computer modeling as the size of the cation increases, presumably due to the void space of the cation which increases with the size of the nitrile ligand.     

Thermal Analysis Studies on Hydroxobridged Homo and Hetero Trinuclear Cobalt(III) Complexes

The synthesis and thermal analysis studies of several hydroxobridged homo and hetero trinuclear cobalt(III) complexes are reported. The complexes are of the type [M(H₂O)_x{(OH)₂Co(en)₂}₂](SO₄)₂ nH₂O and [M(H₂O)_x{(OH)₂Co(NH₃)₄}₂](SO₄)₂nH₂O where en denotes ethylenediamine and M =Co(II), Ni(II), Cu(II) and Zn(II) with x=0 for Cu(II), and 2 for other metal ions, and n =3, 4 or 5. The TG and DTA studies of these compounds show that one or more intermediate compounds are formed in each case before the metal oxides are produced.     

Syntheses,Structures and Characterization of Cobalt(II) and Cobalt(III) Complexes with N-Benzylated Polyamines and a Terminal Azido Ligand

Mononuclear cobalt(II) and cobalt(III) complexes, [Co(trenb)(N₃)]Cl (1) and [Co(dienb)(N₃)₂(OAc)] (2) (trenb = tris[2-(benzylamino)ethyl]amine, dienb = 1,9-diphenyl-2,5,8-triazanonane) were synthesized and characterized by elemental analyses, IR and electronic spectra. Their crystal structures were also determined by X-ray diffraction analyses. In Complex 1, cobalt(II) is five-coordinate trigonal bipyramidal with one azido nitrogen atom and four nitrogen donors of the tripodal ligand; the chloride interacts weakly with one of the secondary amino groups of trenb via a hydrogen bond. In Complex 2, cobalt(III) is in a distorted octahedral coordination environment, consisting of three nitrogen atoms of the amine ligand, two azide nitrogen atoms and an oxygen atom of the acetate ion; a six-membered ring involving the hydrogen bond may stabilize the complex, which maintains its solid geometry in DMF as indicated by the electronic spectrum.