Nickel Di-iodide, NiI₂

Nickelous Iodide or Nickel Di-iodide, NiI₂, may be obtained by heating reduced nickel with iodine, or by dissolving the hydroxide in aqueous hydrogen iodide, evaporating to dryness and subliming in the absence of air. It forms iron-black scales. With ammonia an am- moniate is produced, which is pale yellow in colour. Blue octahedral crystals of the hexa-ammoniate, NiI₂.6NH₃, result when excess of ammonia is added to a solution of the iodide. This loses ammonia on exposure to air, becoming green and ultimately brown.

The hexahydrate, NiI₂.6H₂O, may be obtained by crystallisation from concentrated aqueous solutions. It is bluish green in colour, crystalline but hygroscopic. Its solubility in water is as follows:

Temperature ° C.	0	10	20	40	60	80	100
Grams NiI2 per 100 grams solution.	55.4	57.5	59.7	63.5	64.8	65.2	65.3

The solution absorbs iodine, yielding a brown liquid containing probably a periodide.