Cobalt -dimethylglyoxime complex

Only two techniques allow the determination of cobalt at normal serum or plasma levels. Neutron activation analysis (NAA) [50-55] and adsorptive cathodic stripping voltammetry (ADCSV) of cobalt dimethylglyoxime complexes [38,40] were applicable, the latter being featured by a very low detection limit. 

Because of structural similarities to the vitamin B,2 coenzyme, cobalt(III) complexes of the type RCo(L4) or RCo(L2)2 [L4 = bis(salicylaldehyde)-ethylenediiminate and L2 = dimethylglyoximate, inter alia] have been actively investigated 40, 76, 77, 125). Corresponding acyl complexes have been synthesized 40, 76). However, neither the CO insertion into the Co—-R linkage nor the decarbonylation of the Co—COR moiety has been achieved (77, 125). A probable reason for this was presented in Section II. 

It has been noted (2) that many oxygen-carrying cobalt(II) complexes involve ligands that provide four donor atoms lying in the same plane as the cobalt atoms, such as salen , porphyrin and dimethylglyoxime, DMG, and related ligands. 

Nickel has been determined spectrophotometrically in seawater in amounts down to 0.5 xg/l as the dimethylglyoxime complex [521,522], In one procedure [521] dimethylglyoxime is added to a 750 ml sample and the pH adjusted to 9 -10. The nickel complex is extracted into chloroform. After extraction into 1M hydrochloric acid, it is oxidised with aqueous bromine, adjusted to pH 10.4, and dimethylglyoxime reagent added. It is made up to 50 ml and the extinction of the nickel complex measured at 442 nm. There is no serious interference from iron, cobalt, copper, or zinc but manganese may cause low results. 

In another procedure [522] the sample of seawater (0.5-3 litres) is filtered through a membrane-filter (pore size 0.7 xm) which is then wet-ashed. The nickel is separated from the resulting solution by extraction as the dimethylglyoxime complex and is then determined by its catalysis of the reaction of Tiron and diphenylcarbazone with hydrogen peroxide, with spectrophotometric measurement at 413 nm. Cobalt is first separated as the 2-nitroso-1-naphthol complex, and is determined by its catalysis of the oxidation of alizarin by hydrogen peroxide at pH 12.4. Sensitivities are 0.8 xg/l (nickel) and 0.04 xg/l (cobalt). 

Samples of metal complexes isolated from the final solutions were subjected to microanalysis (for carbon, hydrogen, oxygen, and sulfur). Metals were determined colorimetrically by the following methods— copper as the complex formed with sodium diethyl dithiocarbamate (6) cobalt as the nitroso-R salt complex (7) nickel as the dimethylglyoxime complex (4). 

Alkylcobalt(III) complexes can also be synthesized in aqueous solution. Two of the best-known systems are methylcobalamin and a group of related cobaloximes, and alkylcobalt(III) complexes having ancillary cyanide ligands. As with the chromium(III) system, alkyl cobalt(III) complexes having dimethylglyoxime (DMG) or cyanide ligands can be synthesized by reaction of the cobalt(II) precursor with alkyl halides (Scheme... 

However, the chrommm(III)-capped cobalt(II) complex was not obtained. In contrast, both the corresponding boron-capped cobalt(II) and cobalt(III) dimethylglyoximates were isolated (see Section 2.1). 

This class of reaction is manifested especially by (typically five-coordinated) low-spin d cobalt(II) complexes, such as [Co(II)(CN)5]3-, [Co(II)(DMGH)iB] (DMGHi = dimethylglyoxime, B = axial ligand such as pyridine, triphenylphosphine, etc.) and cob(Il)alamin (vitamin Bn ). Important examples include the oxidative addition of organic halides leading to the formation of organometallic compounds by free-radical mechanisms ... 

Species. This behavior is shown by a relatively small class of (mainly) 4- or 5-coordinated cobalt(II) complexes of quadridentate imine condensates (47, 60, 61, 62, 63), dimethylglyoxime (58), a,p,y,h-... 

Studied. An aetioporphyrin I cobalt(III) methyl complex has been prepared [128] and methyl cobalt(III) phthalocyanine is also known [129]. The dimethylglyoxime complex, 7.23, where R = CN and L = PhsP, pyri-... 

Dimethylglyoxime. The complexes with nickel and with palladium are soluble in chloroform. The optimum pH range for extraction of the nickel complex is 4-12 in the presence of tartrate and 7-12 in the presence of citrate (solubility 35-50 fig Ni mL 1 at room temperature) if the amount of cobalt exceeds 5 mg some cobalt may be extracted from alkaline solution. Palladium(II) may be extracted out of ca lM-sulphuric acid solution. 

The precipitate is soluble in free mineral acids (even as little as is liberated by reaction in neutral solution), in solutions containing more than 50 per cent of ethanol by volume, in hot water (0.6 mg per 100 mL), and in concentrated ammoniacal solutions of cobalt salts, but is insoluble in dilute ammonia solution, in solutions of ammonium salts, and in dilute acetic (ethanoic) acid-sodium acetate solutions. Large amounts of aqueous ammonia and of cobalt, zinc, or copper retard the precipitation extra reagent must be added, for these elements consume dimethylglyoxime to form various soluble compounds. Better results are obtained in the presence of cobalt, manganese, or zinc by adding sodium or ammonium acetate to precipitate the complex iron(III), aluminium, and chromium(III) must, however, be absent. 

Concentration of an ethanolic solution of dimethylglyoxime, cobalt(n) chloride and benzotriazole results in deposition of crystalline complex 68. The product is stable at room temperature however, it slowly decomposes upon heating. Thermal analysis reveals that the compound releases first the chlorine atom and 50% of the benzotriazole content to form a new complex that is stable to 225 °C. Probably in this new form, the benzotriazole moiety coordinates two cobalt ions simultaneously. Further heating to 350 °C removes the benzotriazolyl moieties completely <2003JPY699>. The first step of decomposition can be summarized as follows ... 

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