Sodium tricarbonatocobaltate

Sodium tricarbonatocobaltate(III) 3-hydrate is an olive-green powder insoluble in water. When completely dry, it is stable indefinitely if stored at room temperature in a closed bottle. It decomposes at 93° without melting. Addition of the acid form of a complexing agent results, in many cases, in the formation of the cobalt(III) complex of the ligand with evolution of carbon dio.xide. 

The geometrical isomers of the tris-complex with P-alanine were synthesized by Celap et al., since the method of Ley-Winkler failed. With the hexaamminecobalt-(III) complex the product was c-isomer with a small amount of mer-isomer. The reaction between sodium tricarbonatocobaltate(III) trihydrate and p-alanine in aqueous solution under heating yielded wer-isomer effectively. 

Boas et al. prepared and separated the meridional isomers of the [Co(ai-02)2] type complexes (oti-a2 represents the dianion of the dipeptide H2 i-a2> where ai is the N-terminal residue). Seven methods were used to prepare bis(dipeptidato)-cobaltate(III) complexes (i) by oxygenation of cobalt(II), (ii) from cobalt(II) carbonate, (iii) from sodium tricarbonatocobaltate(III), (iv) from hexaamminecobalt-(III) chloride, (v) from hexakis(urea)cobalt(III) perchlorate, (vi) from cobalt(III) hydroxide oxide, (vii) from triammine(glycylglycinato)cobalt(III). The methods starting from Co" gave more minor products, Na3[Co(C03)3] 3 H2O gave less, and cobalt(III) hydroxide oxide gave very little of these products. Thus, the method (vi) was prefered. The peptides used were gly-gly, L-ala-gly, gly-L-ala, L-leu-gly, gly-L-leu, L-phe-gly, gly-L-phe, L-ala-L-ala, L-ala-D-ala, L-leu-L-leu. 

Some years later, Bauer and Drinkard prepared the hardly soluble sodium salt of tricarbonatocobaltate(III), Na3[Co(C03)3] 3 H2O, in an analogous manner. They used solid sodium salt as the starting material for preparing certain cobaltflll) coordination compounds. 

There is a striking solubility difference between the potassium and sodium salts of tricarbonatocobaltate(III). The concentration of the solution prepared according to Procedure 1 can be made as high as 1 mol/dm with respect to Co(III) however the potassium salt can be isolated only with simultaneous decomposition to hydrous-oxidc-like substances. In contrast, the sodium salt obtained by Procedure 2 is very stable when it is completely dried. The salt is insoluble in water but soluble in water containing sodium bicarbonate. 

Bauer and Drinkard described several features of tricarbonatocobaltate(III) sodium as an intermediate... 

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