Kobalt-Komplexe mit O2-Brücken: Die Struktur der Kationen μ-Hydroxo-μ-peroxo-bis[bis(äthylendiamin) kobalt(III)]3+ und μ-Hydroxo-μ-superoxo-bis[bis (äthylendiamin)kobalt(III)]4+

Cobalt Complexes with O₂ Bridges: The Structure of the Cations μ-Hydroxo-μ-peroxo-bis[bis(ethylenediamine) cobalt (III)]³⁺and μ-Hydroxo-μ-superoxo-bis [bis (ethylenediamine) cobalt (III)]⁴⁺ X-ray structure determinations of one salt of each of the two chemically and structurally closely related dinuclear cobalt cations [(en)₂Co · μ(OH, O₂) · Co(en)₂]³⁺ 1a and [(en)₂Co · μ(OH, O₂) · Co(en)₂]⁴⁺ 1b have been performed. In both cases the cations exist as racemic mixtures of ΔΔ and ΔΔ isomers. The O–O distance in the μ-peroxo cation 1a is 1.465 Å and the Co–O–O–Co torsion angle is 60.7°. The corresponding values for the μ-superoxo cation 1b are 1.339 Å and 22.0°.     

Effect of the Formation of a Charged Intermediate on the Electroreduction of Cobalt(III) Trioxalate Complexes to Cobalt(0) Atoms

Kinetic relationships for the recharge of a cobalt(III) trioxalate complex on a mercury electrode are derived for electrode potentials of 0 to –1.5 V vs. point of zero charge (PZC) of mercury. This wide range includes high negative potentials at which the recharge of Co(C₂O₄)₃ ^3– and discharge of Co²⁺ occur simultaneously. The contribution of the reaction Co(II)/Co(0) (whose kinetic parameters are known) into the overall reduction of Co(C₂O₄)₃ ^3– to metallic cobalt is calculated. Migration fluxes of species present in solution are shown to be insignificant; hence, these can be neglected in the calculations. Relationships, which permit the determination of a partial polarization curve for the Co(III)/Co(II) recharge from the overall rate of the Co(III)/Co(0) process, are found. A quantitative evidence for the appearance of a secondary current drop at potentials near –0.7 V vs. PZC is obtained. The drop is caused by variations in the outer Helmholtz plane potential because of the commence of discharge of Co²⁺.     

Fluorometric Determination of Arsenic(III) with Fluorescein

A rapid, simple, and sensitive fluorometric method has been developed for the determination of arsenic(III) with fluorescein as fluorogenic reagent (λ_ex= 495 nm, λ_em= 516 nm) at pH 5.2–7.0. A linear calibration curve was obtained in the range 0.01–2.5 μg As(III)/25 ml. The detection limit is 0.01 μg As(III)/25 ml. The method was successfully applied to the determination of arsenic(III) in waste- and river water.     

Investigation of A New Catalytic Reaction of Complex Formation of Cobalt (III) With Nitroso-R-Salt for the Determination of Microquantities of Phosphate-Ions

ABSTRACT

The catalytic action of phosphate-ions on the reaction of complex formation of cobalt (III) with nitroso-R-salt in a weakly acid medium has been found. The dependence of the rate of the catalytic reaction on temperature, concentrations of reagents and catalyst, pH of the medium, as well as on the presence of some anion and non-ion surface-active substances and accompanying inorganic minerals was studied. The optimum conditions for the determination of 0.1 μg/ml PO^3- ₄ in water were determined. A technique for the determination of phosphate-ion impurity up to 9×10^-5% in the high-purity sodium iodide and 2×10^-4% cesium iodide used for the single crystals growth is suggested.     

Tetradecyldimethylbenzylammonium thiocyanate adsorbent supported on naphthalene for the preconcentration and determination of cobalt in aluminium alloys and steels using atomic absorption spectrometry

A solid ion-pair material produced from tetradecyldimethylbenzylammonium chloride (TDBA) and ammonium thiocyanate on naphthalene provides a simple, rapid and selective technique of preconcentrating cobalt from up to 200 ml of aqueous solution. Cobalt reacts with sodium 1-nitroso-2-naphthol-3,6-disulphonate (nitroso-R salt) to form a brown, water-soluble chelate anion. The chelate anion forms a water-insoluble Co-nitroso-R salt-TDBA complex on naphthalene packed in a column and trace cobalt is quantitatively retained on the naphthalene in the pH range 2.7–11.0 at a flow-rate of 2 ml min^?1. The solid mass is stripped from the column with 5 ml of dimethylformamide (DMF) and cobalt is measured by atomic absorption spectrometry (AAS) at 241 nm. The calibration graph is linear over the concentration range 0.5–15μg Co in 5 ml of dimethylformamide solution. Seven replicate determinations of 9 μg of cobalt gave a mean absorbance of 0.095 with a relative standard deviation of 1.7%. The sensitivity for 1% absorption was 0.0834μg ml^?1 (0.240 μg ml^?1 for direct AAS on the aqueous solution). The proposed method was utilized for the determination of cobalt in standard aluminium alloys and steel samples.     

“Stat” methods in continuous flow analysis : Determination of Copper,Iron, Iodide and Hydrochloric Acid

A continuous flow “stat” method is described in which a certain arbitrarily imposed state in the flowing stream is automatically maintained by regulating the rate of flow of one of the components. The electronic system is regulated by measuring a physical phenomenon in the flowing solution. The method is illustrated by the examples of a continuous flow absorptiostat [Fe(III)/S₂O₃^2-/Cu(II)]for determinations of copper(II) (1–10 μg ml^-1), iron(III) (25–250 or 12.5–125 μg ml^-1), as well as for determination of iodide (12.8–128 μg ml^-1). A continuous flow conductostat [HCl/NaOH] for determination of 1–2.5 × 10^-4 M HCl is also described. This analytical technique is intended for automatic continuous monitoring of sample streams.     

Pre-column chelation liquid chromatographic separation and determination of trace V,Cu, Co,Pd, Fe and Ni

Conditions for the separation by reversed-phase liquid chromatography (LC) of V(V), Cu(II), Co(III), Pd(II), Fe(III) and Ni(II) chelates with 2-(5-bromopyridylazo)-5-diethylaminophenol (5-Br-PADAP) were studied. Six species of metal chelates were separated successfully with methanol-acetonitrile-water (72:12:16, v/v/v) containing 0.13 M NaCl and 0.29 mM cetyltrimethylammonium bromide (pH 5.0) as the mobile phase on a Nucleosil C₁₈ (5 μm) column (250 × 4 mm i.d.).The conditions of the determination of these metal chelates are discussed. A simple and rapid method for the determination of trace amounts of V(V), Cu(II), Co(III), Pd(II) and Ni(II) simultaneously by reversed-phase LC has been developed. The detection limits are 5 × 10^?12, 1 × 10^?10, 3 × 10^?11, 5.3 × 10^?9 and 2 × 10^?10 g, respectively. The method is applied to the determination of these metals in natural waters and mineral samples.     

Synthesis and characterization of cobalt(III) tetraaza macrocyclic complexes containing chloro and azido ligands

The complexes [Co(L)Cl₂]Cl · 4H₂O (1) and [Co(L)(N₃)₂]N₃ · 2H₂O (2) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo [14,4,0^1.18,0^7.12]docosane) have been synthesized, and structurally characterized by X-ray crystallography, spectroscopy and cyclic voltammetry. The crystal structure of (1) is centrosymmetric and the cobalt(III) atom has an axially elongated octahedral geometry with four nitrogen atoms of the macrocycle and two chloride ligands. The cobalt(III) ion in (2) is coordinated to four nitrogen atoms from the macrocycle, and two azide ligands in an octahedral environment, which forms the 1D polymer through hydrogen bonding contacts involving the cation, azide anion and solvent water molecules. Electronic spectra of the complexes also exhibit a low-spin octahedral environment. Cyclic voltammetry of the complexes undergoes a one-electron wave corresponding to Co(III)/Co(II) processes. The electronic spectra and electrochemical behaviors of the complexes are significantly affected by the nature of the axial ligands.     

The simultaneous determination of As,Cd, Co,Hg, Mo,and Zn in fresh water by neutron activation analysis

A radiochemical neutron activation method for the simultaneous determination of arsenic, cadmium, cobalt, mercury, molybdenum, and zinc in fresh water is described. The method is based on anion-exchange separation in hydrochloric acid media followed by simple precipitations. The determination limits, based on analysis of a 5-ml sample without preconcentration, and with a well-type NaI(Tl) detector, are as follows: As, 10^-3 μg l^-1 ; Cd, 6 × 10^-2 μg l^-1 ; Co, 4 × 10^-3 μg l^-1 ; Hg, 7 × 10^-3 μg l^-1 ; Mo, 10^-1 μg l^-1 ; Zn, 2 × 10^-1 μg l^-1. The method is adequate for the analysis of natural fresh waters.     

Spectrophotometric Determination of Diphenadione Via its Metal Complexes

Abstract

Spectrophotometric procedure is described for the quantitative determination of diphenadione [2-(diphenylacetyl)-1,3-indandione], based on direct spectrophotometric measurements of the absorbances of its iron (III), iron (II) and cobalt (II), metal complexes at 488 nm, 505 nm and (334 nm, 372 nm), respectively. The drug reacts with metals in the ratio of 3:1 and 2:1 for iron (III) and for both iron (II) and cobalt (II) respectively. The obtained complexes have apparent molar absorptivities of 1.48 × 10³ 1 mol^?1 cm^?1, 0.714 × 10³ 1 mol^?1cm^?1 and (1.70 × 10³ 1 mol^?1cm^?1, 1.93 × 10³ 1 mol^?1cm^?1) for iron (III), iron (II) and cobalt (II) complexes, respectively. The procedure is suggested for the determination of 51–400 μg.ml^?1 diphenadione via the iron (II) complex and 35–170 μg.ml^?1 diphenadione via both cobalt (II) and iron (III) complexes. The suggested procedure has accuracies of 99.79 ± 0.67%, 99.64 ± 0.37% and (100.09 ± 0.53%, 99.99 ± 0.42%) for the metal complexes of iron (III), iron (II) and cobalt (II), respectively.     

Simultaneous Determination of Nickel and cobalt in Manganese Sulphate Electrolyte by DMGH2-Sensitized Differential Pulse Polarography

Abstract

A method is described for the simultaneous determination of nickel and cobalt in manganese sulphate electrolyte by the dimethylglyoxime (DMGH₂) sensitized differential pulse polarography. The high manganese sulphate background (1.2M) in the concentrated process plant electrolyte interferes only with the nickel determination and precludes its direct determination. A 50% v/v dilution and an excessive amount (2 × 10^?3M) of the chelating agent are required at pH7.7 for the reliable determination of both elements. Under these conditions, the linear concentration ranges are 0-110 μg/1 for nickel and 0-140 μg/1 for cobalt. The minimum detectable amounts above the levels present in the process plant electrolyte are 2 μg/1 and 1 μg/1 for both elements, respectively. The relative standard deviations for all measurements are between 1 and 3%.     

Trace analysis of mercury by a radiochemical displacement method using cobalt(III) diethyldithiocarbamate

A radiochemical displacement method was utilized for the determination of traces of mercury in water taking advantage of its ability to displace cobalt from cobalt(III) diethyldithiocarbamate tagged with⁶⁰Co. The method is found to be applicable in the concentration range of 50–200 g/ml mercury. The interfernces from various cations like Fe(III), Co(II), Cu(II), Pb(II) and Ag(I) ions were studied.     

Thiobarbituric acid-reacting substances derived from autoxidizing linoleic and linolenic acids

Seven pyridylazo dyes containing the m-tolylenediamine group were synthesized and their analytical potential for the determination of cobalt was studied spectrophotometrically. The molar absorptivities and selectivity of these reagents increased compared with those of PADAB. Cobalt(II) and 3,5-diCl-PADAT (5-[(3,5-dichloro-2-pyridyl)azo]-2,4-diaminotoluene) at pH 3 form a complex which is very stable even in the presence of strong mineral acids. The complex has two absorption maxima at 548 and 590 nm in hydrochloric acid (2.4 M) solution. The color is very stable and the system conforms to Beer's law; the optimal range for measurement in a 1-cm cell is 0.01–0.4 p.p.m. cobalt. In practice, this color reaction is specific. The molar absorptivity is 1.38 ·10⁵ 1 mol^-1 cm^-1 at 590 nm. The sensitivity is 0.00042 μg Co cm^-2 at 590 nm for log I₀/I= 0.001. The method was applied to the determination of cobalt in steel and waspaloy.     

Synthesis,characterization, electrochemical and crystal structure investigation of bis(2-((2-aminoethylimino)methyl)-6-methoxyphenolato) cobalt(III)

The mononuclear cobalt(III) complex [Co(L)₂]Cl ·?H₂O (1) (where L is H₂N(CH₂)₂N=CC₆H₃(OMe)(O^?)) has been prepared and characterized by IR, UV-Vis spectroscopy, conductivity measurements, elemental analysis, TGA, cyclic voltammetry and an X-ray structure determination. The cobalt(III) coordination sphere in [Co(L)2] is cis-CoN₄O₂ with the NNO ligands. Electrochemical studies of 1 using cyclic voltammetry indicate an irreversible cathodic peak (E _pc, ca ?0.60 V) corresponding to reduction of cobalt(III) to cobalt(II).     

New methods for the detection of cyanide based on displacement of the glutathione ligand of glutathionylcobalamin by cyanide

Glutathionylcobalamin (GSCbl) is a vitamin B₁₂ derivative that contains glutathione as the upper axial ligand to cobalt via a Co–S bond. In the present study, we discovered that cyanide reacted with GSCbl, generating cyanocobalamin (CNCbl) and reduced glutathione (GSH) via dicyanocobalamin (diCNCbl) intermediate. This reaction was induced specifically by the nucleophilic attack of cyanide anion displacing the glutathione ligand of GSCbl. Based on the reaction of GSCbl with cyanide, we developed new methods for the detection of cyanide. The reaction intermediate, violet-coloured diCNCbl, could be applied for naked eye detection of cyanide and the detection limit was estimated to be as low as 520 μg L^?1 (20 μM) at pH = 10.0. The reaction product, CNCbl, could be applied for a spectrophotometric quantitative determination of cyanide with a detection limit of 26 μg L^?1 (1.0 μM) at pH = 9.0 and a linear range of 26–520 μg L^?1 (1.0–50 μM). In addition, the other reaction product, GSH, could be applied for a fluorometric quantitative determination of cyanide with a detection limit of 31 μg L^?1 (1.2 μM) at pH = 9.0 and a linear range of 31–520 μg L^?1 (1.2–20 μM). These new GSCbl-based methods are simple, highly specific and sensitive with great applicability for the detection of cyanide in biological and non-biological samples.     

Synthesis,characterization, and electrochemical studies of Co(II,III) dithiocarbamate complexes

Cobalt(II) complexes of N-methyl phenyl, 1-phenylpiperazyl, and morpholinyl dithiocarbamates have been synthesized and characterized by UV–Visible, FTIR, ¹H-, ¹³C-NMR, and mass spectrometry. The spectroscopic data indicated that two ligands coordinated in bidentate chelating to the metal ion to form four-coordinate cobalt(II) complexes (1–3), which was confirmed by mass analysis (TOF MS ES⁺) of the complexes with m/z [M]⁺ = 450.98, 382.94, and 382.94 for 1, 2, and 3, respectively. Single crystal analysis of 2A and 3A show centrosymmetric mononuclear cobalt(III) bonded to three dithiocarbamate ligands forming a distorted octahedral geometry, indicating the cobalt(II) undergoes aerial oxidation to cobalt(III) during recrystallization. In addition, 2A crystallized with one solvated molecule of toluene. The redox behaviors of the complexes were studied by cyclic and square wave voltammetry in dichloromethane; the result revealed a metal centered redox process consisting of a one-electron quasi-reversible process assigned to Co(III)/Co(IV) oxidation and a corresponding Co(IV)/Co(III) reduction. Randles–Sevcik plots (anodic peak current versus the square root of the scan rate (I_p,a versus ν^1/2)) for the redox couples revealed diffusion-controlled behavior.     

Spectrophotometric study of bismuth with N-(2-acetamido)iminodiacetic acid (ADA): Determination of bismuth in pharmaceutical formulations

A new method for the Spectrophotometric determination of bismuth using N-(2-acetamido)iminodiacetic acid as complexometric agent is proposed. The complex is formed in a wide pH range, 5.5–7.5, and has a maximum absorption at 265 nm. Beer's law is obeyed in the interval 3.8–17.9 μg of bismuth(III)/ml, with a minimum photometric error of 2.3. The molar absorptivity is 9.1 × 10³ liters/cm mol. The stoichiometry of the reaction takes place in the metal-to-ligand ratio 1:2. The interferences produced by the more common ions are studied. The method has been successfully applied to the determination of bismuth in pharmaceutical formulations.     

CO2 to CO Electroreduction,Electrocatalytic H2 Evolution,and Catalytic Degradation of Organic Dyes Using a Co(II) meso-Tetraarylporphyrin

The meso-tetrakis(4-(trifluoromethyl)phenyl)porphyrinato cobalt(II) complex [Co(TMFPP)] was synthesised in 93% yield. The compound was studied by ¹H NMR, UV-visible absorption, and photoluminescence spectroscopy. The optical band gap Eg was calculated to 2.15 eV using the Tauc plot method and a semiconducting character is suggested. Cyclic voltammetry showed two fully reversible reduction waves at E_1/2 = −0.91 V and E_1/2 = −2.05 V vs. SCE and reversible oxidations at 0.30 V and 0.98 V representing both metal-centred (Co(0)/Co(I)/Co(II)/Co(III)) and porphyrin-centred (Por²⁻/Por⁻) processes. [Co(TMFPP)] is a very active catalyst for the electrochemical formation of H₂ from DMF/acetic acid, with a Faradaic Efficiency (FE) of 85%, and also catalysed the reduction of CO₂ to CO with a FE of 90%. Moreover, the two triarylmethane dyes crystal violet and malachite green were decomposed using H₂O₂ and [Co(TMFPP)] as catalyst with an efficiency of more than 85% in one batch.     

A potentiometric study of the oxidation of cobalt(II) with gold(III) chloride in presence of 1,10 phenanthroline or 2,2'-bipyridine : A new titration of cobalt (II) and its application to nickel-base alloys

The redox reaction between cobalt(II) and gold(III) chloride in the presence of 1.10-phenanthroline or 2,2'-bipyridine was studied, and a titration of the cobalt(II) complex with a gold(III) chloride solution was developed. A 4-fold amount of 1,10-phenanthroline or 2,2'-bipyridine was necessary for rapid quantitative reaction; the permissible pH range was 1.5–5. The oxidation of the cobalt(II) complex proceeds rapidly at 40–50°C, and a direct potentiometric titration was possible. The following maximum errors were obtained: 3.3% for 0.2–1.0 mg Co, 2.0% for 1–5 mg Co, and 0.70% for 10–40 mg Co. The following ions did not interfere: Ni(II), Zn(II), Pb(II), Cd(II), Mn(II), Fe(II), Cr(III), Al(III), Th(IV), Se(IV), Ti(IV), U(VI), Mo(VI), SO^2-₄ and PO^3-₄. Even small quantities of silver(I), copper(II), palladium(II), mercury(II)and iron(III) interfered. The method was applied to the determination of high cobalt contents in high-temperature nickel-base alloys.     

Redox Speciation of Inorganic Arsenic in Water and Saline Samples by Adsorptive Cathodic Stripping Voltammetry in the Presence of Sodium Diethyl Dithiocarbamate

This paper describes a new voltammetric procedure for the inorganic speciation of As(III) and As(V) in water samples. The procedure is based on the chemical reduction of arsenate [As(V)] to arsenite [As(III)] followed by the voltammetric determination of total arsenic as As(III) at the hanging mercury drop electrode (HMDE) by adsorptive cathodic stripping voltammetry (AdCSV) in the presence of sodium diethyl dithiocarbamate (SDDC). The reduction step involved the reaction with a mixture of Na₂S₂O₅ and Na₂S₂O₃ in the concentrations 2.5 and 0.5 mg mL^?1, respectively, and the sample heating at 80 °C for 45 min. The linear range for the determination of total arsenic as As(III) in the presence of SDDC was between 5 and 150 μg L^?1 for a deposition time of 60 s (r=0.992). A detection limit of 1.05 μg L^?1 for total As was calculated for the method in water samples using a deposition time of 60 s. The detection limits of 4.2 μg L^?1 and 15.0 μg L^?1 for total As in seawater and dialysis concentrates, respectively, were calculated using a deposition time of 60 s. The relative standard deviations calculated were 2.5 and 4.0% for five measurements of 20 μg L^?1 As(V) as As(III) in water and dialysis concentrates, respectively, after chemical reduction under optimized conditions. The method was applied for the determination of As(III) and total As in samples of dialysis water, mineral water, seawater and dialysis concentrates. Recovery values between 86.0 and 104.0% for As(III) and As(V) added to the samples prove the satisfactory accuracy and applicability of the procedure for the arsenic monitoring.