HEXAMMINECOBALTOUS CHLORIDE. 185nitric acid, and, by the addition of more nitric acid, precipitate
out the crystalline hexamminechromic nitrate. Yield, about 7 g.
The residue from the treatment with ice water consists of chloro-
purpureochromic chloride. Boil it in a beaker with concentrated
hydrochloric acid, cool, add some water, collect the salt on a filter
and wash it with a little cold water. Then dissolve the salt as
quickly as possible at 50° in 400 to 500 c.c. of water containing afew drops of sulphuric acid. Filter the solution at once through a
large plaited filter and add an equal volume of concentrated hydro-
chloric acid. Allow the beautiful red crystals which separate to
stand an hour in contact with the mother-liquor, then drain them
and wash first with 20% hydrochloric acid (1 pt. cone. HC1 : 1 pt.
H 2 O), then with alcohol, and dry the product in a desiccator.
Yield, about 5 grams.
Transformation of the Luteo Salt into Chloropurpureo Salt. Mix
a solution of hexamminechromic nitrate, dissolved in eleven
times its weight of hot water, with an equal volume of concen-
trated hydrochloric acid and boil gently for from thirty minutes to
an hour. When the liquid has become cold, filter off the precipi-
tated chloropentammine chromic chloride and wash it as above.
- Hexamminecobaltous Chloride, [Co(NH 3 ) 6 ]CL.
In compounds with a coordination number 4, if the substituents are sup-
posed to be at the corners of a square lying in a plane passing through the
central atom, there is, according to Werner, a possibility of isomerism. Thus,
if the outlying groups consist of two unlike pairs, stereoisomerism will take
place, if, in one case, the two like groups are side by side in neighboring corners
of the square and in the other case the like groups are opposite to one another,
as at the ends of a diagonal of the square. The classic example of this kind
of isomerjsm is found in fo-aras-diamminechloroplatinum and eis-diammine-
chloroplatinum, which have been known for a long time as "chloride of Rie-
set's second base" and "Pyrone's salt." More recently^1 perfectly analogous
derivatives of bivalent cobalt have been prepared, a- and 0-diamminedichloro-
cobalt, which have different colors and are characterized by different ammonia
tensions. The pink alpha compound is the more stable and probably corre-
sponds to the cis-formula:
CK XNH 3 CK ,NH 3
)) (C
a-diamminedichlorocobalt /3-diamminedichlorocobalt
pink blue
(^1) W. Biltz and B. Fetkenheuer, Z. anorg. Chem. 89, 121 (1914).