Tetrammine purpureo-salts [RCo(NH3)4 H20]X2.
Pentammine purpureo-salts [R Co(NH 3) 5 ]X 2 where X = Cl, Br, N03, N02, 1S04, &c.
The pentammine purpureo-salts are formed from the luteo-salts by loss of ammonia, or from an air slowly oxidized ammoniacal cobalt salt solution, the precipitated luteosalt being filtered off and the filtrate boiled with concentrated acids.
They are formed by the action of nitrous fumes on ammoniacal solutions of cobaltous salts, or purpureo-salts, or by the mutual reaction of chlorpurpureosalts and alkaline nitrites.
They are of a reddish colour and usually crystallize well; on heating with concentrated acids are usually transformed into the purpureo-salts.
The purpureo chloride has only two-thirds of its chlorine precipitated on the addition of silver nitrate, and the electric conductivity is much less than that of the luteo chloride; again in the praseosalts only one-third of the chlorine is precipitated by silver nitrate, the conductivity again falling; while in the triammine salts all ionization has disappeared.
H 2 0],thechlorpentammine or purpureo-chromium salts, R 1 2 [Cr(NH 3) 5 Cl], the nitrito pentammine or xanthochromium salts, R 1 2[N02 (NH3)5 Cr], the luteo or hexammine chromium salts, R 1 3[(NH3) 6 Cr], and the rhodochromium salts: where R 1 = a monovalent acid radical and M = a monovalent basic radical.