Dithionate, Bromide, Chloride, and Perchlorate

DI-ai-HYDROXO-BIS[BIS(ETHYLENEDIAMINE)COBALT(III)] DITHIONATE, BROMIDE, CHLORIDE, AND PERCHLORATE 

Di-/Li-hydroxo-bis[bis(ethylenediamine)cobalt(III)] dithionate may be obtained analogously to the chromium(III) salt from cis- [aquabis(ethylenediamine)hydrox-ocobalt(III)] dithionate, either by heating at 110° or by refluxing in acetic anhydride. The formation of the bridged cation of cobalt(III) is much slower than that of chromium(III). In contrast to the chromium(III) complex there is no evidence that the bridged cobalt(III) complex can be formed by aqueous hydrolysis. 

In the procedure given below, di-/a-hydroxo-bis[bis(ethylenediamine)cobalt-(III)] dithionate is obtained quantitatively from ds-[aquabis(ethylenediamine)-hydroxocobalt(III)] dithionate by refluxing in acetic anhydride. The ds-[aqua-bis(ethylenediamine)hydroxocobalt(III)] dithionate is obtained from carbo-natobis(ethylenediamine)cobalt(III) chloride.  

The bromide and the chloride are obtained from the dithionate by modifications of the procedures given in the literature.The perchlorate is obtained from the bromide. Other salts, such as the iodide, thiocyanate and nitrate, have been described in the literature. 

Crude ds-[aquabis(ethylenediamine)hydroxocobalt(III)] dithionate (40.0 g, 0.107 mole) is added to 400 mL of acetic anhydride. The suspension is refluxed for 3 hours. The crude di-/i-hydroxo-bis[bis(ethylenediamine)cobalt(III)] dithionate is isolated analogously to the chromium(III) complex as mentioned in Section 15-J. Yield is 34.0 g (89%) of a crude, almost pure product. 

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Methods for the preparation and purification of salts of the dimeric complex ions di-/i-hydroxo-bis[tetraamminechromium(III)] and di-p-hydroxo-bis [bis-(ethylenediamine)chromium(III)] and of the two corresponding cobalt(III) species are presented. The two ammine complex dimers are isolated as bromide and perchlorate salts. The two ethylenediamine complexes are isolated as dithionate, bromide, chloride, and perchlorate salts. All four dimers have been obtained by heating the corresponding cis-aquahydroxo complexes as the dithionate salts. 

The inertness of the dinuclear complexes is greatest in slightly acidic solutions, which therefore have been employed for the reprecipitation reactions. Apparently the chromium systems are much more labile toward bridge breaking than are the cobalt systems. In aqueous solution the meso-[(en)2Cr(OH)2Ci(en)2] cation (I) enters into a rapidly established (t 1 min. at room temperature) equilibrium with the mono-ju-hydroxo complex [(OHXen)2Cr(OH)Cr(en)2-(HaO)] (n) The equilibrium constant K = [II]/[I] is 0.83 in 1 Af NaC104 at 0°. The salts (dithionate, bromide, chloride, and perchlorate) of the di-p-hydroxo cation are less soluble than the respective salts of the mono-/i-hydroxo cation. It is therefore possible to precipitate the pure salts of the di-/i-hydroxo cation from the equilibrium mixture following the procedure given above. 

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