Vanado-phosphates

Alkali vanado-phosphates are numerous, and contain from one to twelve molecules of vanadium pentoxide in combination with one molecule of phosphorus pentoxide. Those with high vanadium pentoxide content are red, crystalline substances, and are called purpureo-compounds; those with low vanadium pentoxide content form yellow crystals, and are styled luteo-compounds.

These are prepared by dissolving vanadium pentoxide in solutions of alkali phosphates. The following are known:

7(NH₄)₂O.P₂O₅.12V₂O₅.26H₂O or (NH₄)₇[P(V₂O₆)₆].13H₂O;
5(NH₄)₂O.P₂O₅.12V₂O₅.44H₂O or (NH₄)₅H₂[P(V₂O₆)₆].21H₂O;
7K₂O.P₂O₅.12V₂O₅.26H₂O or K₇[P(V₂O₆)₆].13H₂O;
5K₂O.P₂O₅.10V₂O₅.26H₂O or K₅H₂[P(V₂O₆)₅O].12H₂O;

together with caesium and rubidium compounds analogous to the last member of the above.

These are prepared by adding excess of phosphoric acid to solutions of alkali vanadates. The following are known:

(NH₄)₂O.P₂O₅-V₂O₅.1 or 3H₂O or ;
(NH₄)₂O.P₂O₅.2V₂O₅.5 or 7H₂O or or 7H₂O;
2K₂O.P₂O₅.V₂O₅ or
K₂O.P₂O₅.2V₂O₅.6 or 7H₂O; 3K₂O.2P₂O₅.2V₂O₅.5H₂O; 3K₂O.4P₂O₅.6V₂O₅.2lH₂O.

A free acid having the composition 2HVO₃.2HPO₃.9H₂O or

has been obtained in golden-yellow leaves by the action of vanadium pentoxide on syrupy phosphoric acid.