Nickel Iodate, Ni(IO₃)₂

Nickel Iodate, Ni(IO₃)₂, discovered by Rammelsberg, is interesting on account of its hydrates. The anhydrous salt is obtained as microscopic yellow needles by heating to 100° C. a mixture of nickel nitrate, iodic acid, and nitric acid. It is but slightly soluble in water, the solubility decreasing with rise of temperature.

Temperature ° C.	30	50	75	90
Grams Ni(IO3)2 in 100 grams solution.	1.135	1.07	1.02	0.988

A monohydrate, Ni(IO₃)₂.H₂O, was obtained by Rammelsberg as a bright green powder by concentrating solutions of nickel sulphate and sodium iodate or a solution of nickel hydroxide in aqueous hydriodic acid. Clarke was unable to find this salt.

The dihydrate, Ni(IO₃)₂.2H₂O, exists in two isomeric forms known respectively as the α and β varieties.

The α-salt is obtained by allowing a mixture of nickel nitrate and iodic acid to stand for several days at 25° to 30° C., when a crystalline mass is formed. It is but slightly soluble in water.

Temperature ° C.	0	18	30	50 (transition temperature)
Grams Ni(IO3)2 in 100 grams solution.	0.53	0.68	0.86	1.78

At 50° C. in the presence of water the α-salt is converted into the β-salt, which crystallises in small prisms which are even less soluble in water. Thus:

Temperature ° C	8	18	50	75	80
Grams Ni(IO3)2 in 100 grams solution.	0.52	0.55	0.81	1.03	1.12

The trihydrate, Ni(IO₃)₂.3H₂O, was first described by Ditte, who evaporated slowly a mixed solution of nickel nitrate and an alkaline iodate. The salt crystallises out in green transparent prisms.

The tetrahydrate, Ni(IO₃)₂.4H₂O, separates out as green hexagonal prisms when a solution of nickel nitrate and sodium iodate is concentrated between 0° and 10° C. The solubility of the salt is as follows:

Temperature ° C	0	18	30
Grams Ni(IO3)2 in 100 grams solution	0.73	1.01	1.41

The hexahydrate, Ni(IO₃)₂.6H₂O, was prepared by Clarke by dissolving nickel carbonate in aqueous iodic acid and allowing to slowly evaporate. The salt yields small green crystals of density 3.70 at 22° C.

Two Periodates of nickel have been described, namely, the meso salt, Ni₃(IO₅)₂, and the diperiodate, Ni₂I₂O₉. The former is obtained as a greenish yellow amorphous salt by the action of nickel sulphate on a solution of Na₂H₃IO₆ when, on boiling, the salt separates out as a flocculent precipitate. Ni₂I₂O₉ occurs as a black crystalline salt obtained by drying at 100° C. the bluish green gelatinous precipitate resulting from mixing solutions of nickel sulphate and K₄I₂O₉.