Metaphosphate

A metaphosphate ion is an oxyanion that has the empirical formula PO−
3. The structure of a metaphosphate ion can be described as being made up of PO₄ structural units in which each unit shares two corners with another unit. This can come about in two ways.

Metaphosphates can be considered as salts of the corresponding metaphosphoric acids (H_nP_nO_3n) although none of these acids has been isolated. The metaphosphoric acids can be formulated as H₂O·P₂O₅. In comparison, phosphoric acid, H₃PO₄ can be formulated as 3H₂O·P₂O₅ and pyrophosphoric acid, H₄P₂O₇, as 2H₂O·P₂O₅.