Potassium tetranitrodiamminecobaltate III

Many salts containing the tetranitrodiamminecobaltate-(III) ion have been prepared, usually by metathetical reactions involving the ammonium - and potassium salts. 

Syntheses of the latter have employed large excesses of reagents compared to the quantity of starting cobalt(II) salt. The following procedure is shorter, uses smaller amounts of materials, and gives a pure product in the same or better yield than the previously available methods. 

A solution of 40 g. (0.17 mol) of cobalt(II) chloride 6-hydrate in 100 ml. of water is added to a mixture of 60 g. (0.87 mol) of sodium nitrite, 35 g. (0.65 mol) of ammonium chloride, and 12 ml. of concentrated aqueous ammonia (ca. 0.18 mol) in 300 ml. of w ater. The mixture is placed in a 1-1. filter flask fitted with a stopper and a lO-mm.-i.d. inlet tube reaching to wdthin in. of the bottom of the flask. Air is drawn vigorously through the liquid for 90 minutes. 

The resulting dark-brown liquid containing a little yellow powder is mixed with 30 g. (0.40 mol) of potassium chloride and allowed to stand in a 12- to 15-in. evaporating dish for 

2 to 4 days. At the end of this time, crystallization is complete, and the mother liquor has only a pale yellow-brown color the volume is 400 ml. 

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Potassium tetranitrodiamminecobaltate(III), synthesis 45 Salts of dinitrodiglycinatocobaltate(III), synthesis 46... 

Potassium tetranitrodiamminecobaltate(III) is a lustrous yellow to brown solid, the exact color depending on the crystal size. It is only very slightly soluble in cold water the solubility at 100° is about 5 g./lOO ml. of water. Prolonged contact with water at temperatures above 50 to 60° causes decomposition. Treatment with excess 10% aqueous oxahc acid yields potassium dinitrooxalatodiamminecobal-tate(III). Silver or mercury (I) nitrate causes the precipitation of the corresponding sparingly soluble metal salts of the anion. The free acid is also relatively stable. Aqueous ethylenediamine displaces nitrite from the complex to give the nonelectrolyte trinitro (ethylenediamine) amminecobalt-(III). ... 

Potassium tetranitrodiamminecobaltate(III) can be used as the starting material for syntheses in the diammineco-balt(III) series. 

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