Cobalt complexes oxalic acid

Tinnemans et al.132 have examined the photo(electro)chemical and electrochemical reduction of C02 using some tetraazamacrocyclic Co(II) and Ni(II) complexes as catalysts. CO and H2 were the products. Pearce and Pletcher133 have investigated the mechanism of the reduction of C02 in acetonitrile-water mixtures by using square planar complexes of nickel and cobalt with macrocyclic ligands in solution as catalysts. CO was the reduction product with no significant amounts of either formic or oxalic acids... 

The reaction of potassium cu,cts-diamminedinitrocarbonatocobaltate(III) hemi-hydrate with oxalic acid gives a rranr-diammine isomer of this complex. The c/r.cw-isomer is obtained by the reaction of c/s. cw-diamminediaquaoxalato-cobalt(ILI) ion with nitrite ion. 

A reversal of the elution order for metals such as lead, cobalt, zinc, and nickel is obtained with the use of oxalic acid as a single complexing agent. Under these chromatographic conditions, the metal separation is controlled by anion and cation exchange processes. The degree to which each mechanism contributes to the separation process depends on the stability of the oxalate complexes (see Table 4-5) and is, therefore, different for each metal ion. The anion exchange... 

Sulphuric acid is not recommended, because sulphate ions have a certain tendency to form complexes with iron(III) ions. Silver, copper, nickel, cobalt, titanium, uranium, molybdenum, mercury (>lgL-1), zinc, cadmium, and bismuth interfere. Mercury(I) and tin(II) salts, if present, should be converted into the mercury(II) and tin(IV) salts, otherwise the colour is destroyed. Phosphates, arsenates, fluorides, oxalates, and tartrates interfere, since they form fairly stable complexes with iron(III) ions the influence of phosphates and arsenates is reduced by the presence of a comparatively high concentration of acid. 

Numerous d cobalt(III) complexes are known and have been studied extensively. Most of these complexes are octahedral in shape. Tetrahedral, planar and square antiprismatic complexes of cobalt(lII) are also known, but there are very few. The most common ligands are ammonia, ethylenediamine and water. Halide ions, nitro (NO2) groups, hydroxide (OH ), cyanide (CN ), and isothiocyanate (NCS ) ions also form Co(lII) complexes readily. Numerous complexes have been synthesized with several other ions and neutral molecular hgands, including carbonate, oxalate, trifluoroacetate and neutral ligands, such as pyridine, acetylacetone, ethylenediaminetetraacetic acid (EDTA), dimethylformamide, tetrahydrofuran, and trialkyl or arylphosphines. Also, several polynuclear bridging complexes of amido (NHO, imido (NH ), hydroxo (OH ), and peroxo (02 ) functional groups are known. Some typical Co(lll) complexes are tabulated below ... 

Other acid radicles may be united with cobalt in the complex for instance, potassium cobalti-eyanide, [Co(CX)6]K3, and potassium eobalti-oxalate, [Co(C204)3]K3.2... 

EDTA (ethylenediaminetetraacetic acid) forms stable metal chelates with a number of metal ions. Using this reagent as a complexing- agent, arsenic, bismuth, and selenium can be determined without any interference in the presence of nickel and cobalt. The cobalt-EDTA chelate is stable in 5 M HCl solution, whereas the corresponding bismuth complex is not. The influence of copper on the determination of arsenic can also be eliminated with EDTA, but not in the determination of selenium. Thiourea has been used to eliminate the influence of copper in the determination of antimony and sodium oxalate to eliminate the influence of copper and nickel in the determination of tin. An addition of thiosemicarbazide and 1,10-phenanthro-line reduces the interference of copper, nickel, platinum, and palladium in the determination of arsenic. 

The addition of excess sodium oxalate to solutions of copper or cobalt salts likewise produces complex double oxalates. Consequently the presence of free acid can then be detected by means of indicators in these cases also. 

Multidentate Leaving Groups.—The hydrolysis of [Co(ox)a] - and of [Co(ox)2(OH2)2], which ultimately produces cobalt(n) and carbon dioxide, involves the formation of an intermediate containing a unidentate oxalate ligand previous to the rate-determining step. Free radical intermediates are thought unlikely in the decomposition of these oxalato-complexes, but malonate ion-radicals are thought to be intermediates both in the thermal and photochemical hydrolysis of the [Co(mal)3] anion. Kinetics are reported for a third example of these aquation-redox processes, [Co(acac)2] in acidic solution. ... 

Cobalt(m).— Anation of [Co(NH3)6(OH2>] + by sulphate or chloride proceeds by a dissociative interchange mechanism, in which the reactive species are ion-pairs and ion-triplets, The activation enthalpy for anation of [Co(NH3)6(OHa)] + by glycine is 29 kcal mol again a dissociative mechanism is operative. An earlier study of oxalate anation of [Co(en)a(OH2)2] in acidic solution is complemented by a study of oxalate anation of [Co(en)a(OH2)(OH)] + in basic solution. Several examples of anation reactions of bridged dicobalt complexes have been mentioned in the section on aquation of these complexes. ... 

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