Spectrophotometric determination of cyanocobalamin (as cobalt)

A spectrophotometric method for the determination of cyanocobalamin (as cobalt) in pharmaceutical preparations has been developed. The sample is first decomposed with sulfuric acid and potassium perchlorate. The liberated cobalt is then determined using 2,2′-dipyridyl-2-pyridylhydrazone as reagent in solutions containing 20% sulfuric acid. The presence of other metal cations does not interfere with the determination of cobalt. The method has been applied to the determination of cobalt in pure cyanocobalamin and in two pharmaceutical preparations.     

Preparation and properties of trimethyltris(dimethylphenylphosphine)cobalt(III)

Summary Trimethyltris(dimethylphenylphosphine)cobalt(III) has been prepared by the reaction of dimethyl(2,4-pentanedionato) bis(dimethylphenylphosphine)cobalt(III) with methyllithium in the presence of one equivalent of dimethylphenylphosphine in diethyl ether at 0°. The reaction of the trimethylcobalt(III) complex with 2,4-pentanedione in diethyl ether gave the starting dimethylcobalt complex with evolution of methane (one mol).     

(eta 5-Cyclopentadienyl)(kappa 3-hydrotris(pyrazolyl)borate)cobalt(II)--the first high-spin cobalt organometallic complex

(eta 5-Cyclopentadienyl)(kappa 3-hydrotris(pyrazolyl)borate)-cobalt(II) has been synthesised; magnetic and crystallographic data indicate this to be the first example of a high-spin cobalt organometallic complex whilst its pentamethylcyclopentadienyl analogue is found to have a low-spin electronic configuration.     

Spectral and magnetic studies on normal cobalt(II) planar and cobalt(III) octahedral, spin-crossover cobalt(III) octahedral and planar-tetrahedral cobalt(II) carbodithioates

Five cobalt(II) complexes, a normal complex Co(4-PPipzcdt)₂ (4-PPipzcdt = 4-phenylpiperazine-1-carbodithioate), and four zwitterionic complexes, Co(4-PPipzcdtH)₂X₂ and Co(4-MPipzcdtH)₂X₂ (X = Cl, Br; 4-PPipzcdtH = 4-phenylpiperazine-1-carbodithioic acid, 4-MPipzcdtH = 4-methylpiperazine-1-carbodithioic acid), have been synthesized. Normal cobalt(III) complexes of the type Co(4-MPipzcdt)₃ and Co₂ {2-MPipz(cdt)₂}₃ (2-MPipz(cdt)₂ = 2-methylpiperazine-1,4-dicarbodithioate) and two zwitterionic cobalt(III) complexes of the type Co(4-MPipzcdtH)₃X₃ (X = Cl, Br) have also been obtained. In addition to the room temperature IR and electronic spectra and magnetic susceptibility studies, all the complexes, except the normal Co(4-MPipzcdt)₃ and Co(4-PPipzcdt)₂ and zwitterionic Co(4-MPipzcdtH)₃Cl₃, have been investigated by variable-temperature magnetic susceptibility measurements. The results of the variable-temperature magnetic susceptibility studies suggest that two cobalt(II) carbodithioates exhibit a square planar-tetrahedral equilibrium, while two cobalt(III) octahedral carbodithioates show a spin-crossover phenomenon.     

N-monoaryldithiocarbamate cobalt(III) complexes(1)

Summary Diamagnetic cobalt(III) complexes of the type (RHNCS₂)₃Co [R = Ph, XC₆H₄ (X=p-Me,p-OMe,p-Cl,p-Br andp-I) and 2,4-Me₂C₆H₃] have been synthesised by reaction of the corresponding dithiocarbamate ammonium salts and hexaaquocobalt(II) chloride. Ligand field parameters calculated from visible spectral data indicate strong covalent character for the Co-S bond. The i.r. spectral data reveal that the CN bond in these dithiocarbamates has less double bond character compared to the corresponding dialkyldithiocarbamates.     

Interpretation of the absorption spectra of the hexaaquo cobalt(II) and hexammine cobalt(II) ions

The absorption spectra of the complex ions [Co(H₂O)₆]²⁺ and [Co(NH₃)₆]²⁺ in solution have been studied. The spectra were analyzed after breakdown of the bands into their Gaussian components by means of the formalism of a crystal field with irregular octahedral symmetry. It has been shown that interpretation of the spectra is possible only with allowance for spin-orbital coupling and orthorhombic distortion. The results obtained differ significantly from the published data.     

Experimental evidence for cobalt(III)-carbene radicals: key intermediates in cobalt(II)-based metalloradical cyclopropanation

New and conclusive evidence has been obtained for the existence of cobalt(III)-carbene radicals that have been previously proposed as the key intermediates in the underlying mechanism of metalloradical cyclopropanation by cobalt(II) complexes of porphyrins. In the absence of olefin substrates, reaction of [Co(TPP)] with ethyl styryldiazoacetate was found to generate the corresponding cobalt(III)-vinylcarbene radical that subsequently dimerizes via its γ-radical allylic resonance form to afford a dinuclear cobalt(III) porphyrin complex. X-ray structural analysis reveals a highly compact dimeric structure wherein the two metalloporphyrin units are arranged in a face-to-face fashion through a tetrasubstituted 1,5-hexadiene C(6)-bridge between the two Co(III) centers. The γ-radical allylic resonance form of the cobalt(III)-vinylcarbene radical intermediate could be effectively trapped by TEMPO via C-O bond formation to give a mononuclear cobalt(III) complex instead of the dimeric product. The allylic radical nature and related reactivity profile of the cobalt(III)-carbene radical, including its inability to abstract hydrogen atoms from toluene solvent, were established by DFT calculations.     

Oxidation of plutonium by cobalt(III) green

A stable green solution of tricarbonatocobaltate(III) has been prepared and used for the redox titrimetric determination of plutonium in HNO₃ medium. Quantitative oxidation could be achieved and excess oxidant could be destroyed by NaNO₂. Pu(VI) was deter-ined by adding known excess of Fe(II) and carrying out potentiometric titration. The precision at the level of 0.5–5.0 mg was 2% RSD.     

Periodic precipitation of cobalt(II) oxinate

The conditions for obtaining periodic precipitation of cobalt(II) oxinate in agar-agar gel are investigated. The dependence of the nature of periodic precipitation on the concentrations of inner and outer electrolytes is studied in detail. The spacing law of Jablczynski and the time law of Morse and Pierce are verified in this system. The dependence of velocity constant (K) and the spacing coefficient (p) on the concentrations of inner and outer electrolytes has been studied. The velocity constant shows a nonlinear variation with the concentrations of the inner and outer electrolytes. The spacing coefficient (p) is inversely proportional to the concentrations of the inner and outer electrolytes. According to Shouji Shinohara's revised flocculation theory, the flocculation values are computed. The dependence of the flocculation value on the concentrations of the outer and inner electrolytes is studied.     

Thermal analysis of some hydrated cobalt(II) alkanesulfonates

The cobalt(II) salts of some alkanemono- and disulfonic acids have been prepared; all are new and most of them crystallized with six molecules of water. Their behaviour under heating has been studied by thermogravimetric analysis (TG) and differential thermal analysis (DTA). Most of them lose their water in several steps and some anhydrous salts melt; the decomposition begins at a temperature which depends upon the structure of the organic anion and it leads to residues, the composition of which depends on the surrounding atmosphere.     

Cleavage by halogens of carboncobalt bonds in organometallic complexes of cobalt(III) : II. Organobis(dimethylglyoximato)cobalt(III) complexes

The reaction between organocobaloximes and ICl in chloroform has been studied. In absence of an excess of added chloride ion the reaction is electrophilic in character; in presence of an excess of chloride ion both oxidative dealkylation and radical attack can occur.     

Sorption of small amounts of cobalt(II) on iron(III) oxide

Summary The sorption of small amounts of cobalt(II) on iron (III) oxide has been studied as a function of pH. The mechanism of sorption is discussed. Iron (III) oxide carrier can be used for the preconcentration of small or trace amounts of cobalt(II). The influence of EDTA, glycine,L(+)-arginine andL(+)-cysteine on the sorption yields of cobalt(II) has also been studied.

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Zusammenfassung Die Abhängigkeit der Adsorption geringer Mengen Co (II) an Eisen (III)-hydroxid vom pH wurde untersucht und der Mechanismus der Adsorption erörtert. Eisen (III) oxidträger kann für die Anreicherung kleiner Mengen oder Spuren Co(II) verwendet werden. Der Einfluß von ÄDTA, Glycin, L(+)-Arginin und L(+)-Cystein auf die sorbierte Menge Co(II) wurde gleichfalls geprüft.

     

Simultaneous determination of cobalt(III)-copper(II) and cobalt(III)-nickel(II) mixtures by differential kinetic methods

A procedure is reported for the simultaneous determination of binary mixtures of cobalt(III)-copper(II) and cobalt(III)-nickel(II) by differential kinetic methods based on complex formation reactions with 3-(1H-1,2,4-triazolyl-3-azo)-2,6-diaminotoluene. The single-point method is used in both cases. The simultaneous determination of Co-Cu and Co-Ni is possible in the concentration range from 10/1 to 1/1. The interference caused by various ions is also studied. The method has been used to determine cobalt-copper and cobalt-nickel mixtures in synthetic samples, hydrofining catalysts and low alloy steels.     

Cleavage by halogens of carboncobalt bonds in organometallic complexes of cobalt(III) : IV. Kinetics and mechanism of the reactions of organobis(dimethylglyoximato) cobalt (III) complexes with iodine in methanol

The mechanism of the reaction between the organocobaloximes RCo(DH)₂H₂O (DH = dimethylglyoximate) and iodine in methanol has been studied and a comparison made with the corresponding reaction in chloroform. The effect of the solvent on the reaction mechanism and the role of nucleophilic assistance are discussed.     

Spectrophotometric determination of cobalt with cobaltone-I (p-nitrophenylhydrazone of diacetylmonoxime)

Summary Cobalt(II) in ammoniacal solution forms a pink, water soluble complex with Cobaltone-I (p-nitrophenylhydrazone of diacetylmonoxime) in the p_H range 11.7–11.9 with absorption peak at 520 nm. The system obeys Beer's Law in the concentration range 0.5–5 ppm of cobalt. Effect of different variables on the colored complex has been studied in detail and optimum conditions determined. Most of the common anions do not interfere with the reaction. The tolerance limits of the cations (other than cobalt) forming soluble amines have been determined. Alkali cyanide raises these limits considerably.Note. For the sake of convenience only, the reagent has been given the trivial name, Cobaltone-I and is referred to as such in the following pages     

Reaction between cobalt(III) acetylacetonate and trimethylaluminium

The reaction between cobalt(III) acetylacetonate and trimethylaluminium at a molar ratio of Me₃Al/Co(acac)₃ of 1/1 has been investigated. When a benzene solution of trimethylaluminium was added to a benzene solution of cobalt (III) acetylacetonate, IR spectra and volumetric gas analysis show that the latter is reduced via stable cobalt(II) acetylacetonate to metallic cobalt. Aluminium(III) acetylacetonate was also formed. The gaseous produts of this reaction were methane, ethane, and ethylene. A reaction mechanism is suggested.     

Kinetic determination of trace cobalt(II) by visual autocatalytic indication

A highly sensitive and simple visual autocatalytic method has been developed for the determination of trace cobalt. The cobalt ion released by the oxidative decomposition of inert bis[2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropyl-amino-phenolato] cobaltate (Co(III)-5-Br-PAPS) with peroxomonosulfate acts as a catalyst for the oxidative degradation of the complex. Thus a definite time lapse of degradation is observed by the sudden disappearance of colored Co(III) complexes. The degradation time varies inversely with the logarithm of the initial concentration of cobalt(II). The determination range of cobalt(II) was from 3x10(-9) to 2x10(-7) M in the presence of 5x10(-6) M of 5-Br-PAPS. The relative standard deviation of the spot size method (10 mul) was 3.5% at 1x10(-7) M cobalt(II). This autocatalytic indicator reaction system has been successfully applied for the visual determination of urinary cobalt.     

Spectrophotometric determination of cobalt(II) with 2-[di-(2-pyridyl)-methylidenehydrazino]quinoline

A simple, rapid and selective procedure for spectrophotometric determination of cobalt has been developed. Cobalt(II) forms two water-soluble complexes with 2-[di-(2-pyridyl)methylidenehydrazino]quinoline, an orange-yellow complex (lambda(max) 510 nm) in the pH range 2-12 and a pink complex (lambda(max) 530 nm) in 0.1-6M perchloric acid medium. The molar absorptivities for the orange-yellow and pink complexes are 3.65 x 10(4) and 4.1 x 10(4) 1.mole(-1).cm(-1) and Beer's law is obeyed up to 1.84 and 2.0 ppm of cobalt(II) respectively. Cobalt(II) has also been determined in alloys.     

Diazabutadiene cobalt(II) complexes

Summary Studies on the chelates of cobalt(II) with the bidentate ligands 1,4-diphenyl(2,3-dimethyl-1,4-diazabutadiene) (PMB) and 1,4-di(p-methoxyphenyl)-2,3-dimethyl-1,4-diazabutadiene (MPMB) have been carried out. On the basis of elemental analyses, the complexes are [Co(PMB)Cl₂], [Co(PMB)₂(C1O₄)₂], [Co(MPMB)Cl₂] and [Co(MPMB)₂(ClO₄)₂].Both ligands are bidentatevia nitrogen atoms in all the complexes. The magnetic susceptibility and i.r. and u.v.-visible spectra are reported and discussed. The chloro-compounds involving two chlorine ligands and, in the perchlorate compounds, the ClO ₄ ^– groups are bound to the cobalt(II) centre.     

Synthesis and crystal structure of polymer cobalt(II) complex, 1,2,4,5-benzenetetracarboxylate hexaimidazole tetraaqua cobalt (II) tetrahydrate

The crystal structure of the title complex {[Co(TCB)2/2-(IMI)2(H2O)2][Co(IMI)4(H2O)2] } (H2O)4 (where TCB = 1,2,4,5-benzenetetracarboxylic anion; IMI = imidazole) has been determined by X-ray diffraction method. Crystal data for {[Co(TCB)2/2(IMI)2(H2O)2][Co(IMI)4(H2O)2]}-(H2O)4: triclinic, space group P 1, a = 1.0647(2) nm, b = 1.1165(1)nm,c = 1.00361(1)nm,α = 91.56(1)°,β = 111.34(1)°, γ = 115.642(10)°, V = 0.9772(3) nm5, Z = 1. The polymer cobalt (II) complex has a novel three-dimension network structure. Co(1) atom and Co(2) atom both are coordinated in an octahedral arrangement and located in the center of the coordination anion and the center of the coordination cation, respectively. Moreover four carboxyl groups of TCB are divided into two types, two para-carboxyl groups bridge Co(1) atom in monodentate fashion and other two para-carboxyl groups are in free.