Intermediate Vanadium Oxides

Oxides which are intermediate between hypovanadic oxide, VO₂, and vanadium pentoxide, V₂O₅, are known. By the partial reduction of vanadium pentoxide, or by the partial oxidation of one of the lower oxides, there have been prepared a number of oxides which are best considered as being formed by the combination of the acidic vanadium pentoxide with a lower basic oxide in varying molecular proportions. These oxides react with alkalis, and yield a series of salts called vanadyl vanadates, intermediate in composition between the vanadites and the vanadates.

2VO.V₂O₅ is produced as a dark blue, crystalline powder when either vanadium pentoxide or ammonium metavanadate is heated with excess of powdered arsenic, or when ammonium metavanadate is reduced with sulphur dioxide at a red heat. It dissolves in nitric acid to a blue solution.

6VO₂.V₂O₅ is obtained as a dark blue or black powder with a metallic lustre by dissolving vanadium pentoxide in caustic potash.

2VO₂.V₂O₅ also results as deep blue crystals on heating ammonium metavanadate which has previously been fused and cooled. It is stated that the fused substance does not furnish vanadium pentoxide on being decomposed. The residue is extracted with concentrated ammonium hydroxide solution and the oxide precipitated by addition of water. The product is slightly soluble in concentrated nitric acid and is readily attacked by hydrochloric acid. It is a little doubtful if the oxide prepared in this manner is not an ammonium vanadyl vanadate. A dark green hydrate, 6VO₂.3V₂O₅.8H₂O, has been obtained by the gentle ignition of ammonium vanadyl vanadate, 3(NH₄)₂O.4VO₂.4V₂O₅. 6H₂O.

VO₂.V₂O₅.4H₂O results on the exposure of vanadous oxide, V₂O₃, to air for several months.

Several other purple, green, or orange intermediate oxides of doubtful composition have been reported.