Nickel Metaphosphate, Ni(PO₃)₂

The anhydrous salt of Nickel Metaphosphate, Ni(PO₃)₂, is obtained by the action of phosphoric acid on nickel sulphate at 300° C. It is a yellow substance, insoluble in water and most acids, but attacked by concentrated sulphuric acid. It may be obtained in the crystalline form by melting with metaphosphoric acid.

A polymeride of this salt, namely, Nickel Hexametaphosphate, [Ni(PO₃)₂]₃ or Ni₃P₆O₁₈, is obtained as a green, gelatinous precipitate on addition of the corresponding sodium salt to a concentrated solution of nickel chloride.