Group 15 Oxides
P4O6 (oxidation state of P is +3) and P4O10 (oxidation state of P is +5) are known: they both have tetrahedral cage structures, the difference being that the terminal cage positions are occupied in P4O10 whereas they are not in P4O6.
terminal positions of tetrahedron unoccupied
terminal positions of tetrahedron occupied
The oxides of P both react with water to give acids, P4O6 giving phosphorous acid H3PO2, and P4O10 giving phosphoric acid H3PO4. The rapid reaction of P4O10 with water means that it is often used as a drying agent.P4O6 is formed when phosphorus is burnt in an insufficient supply of oxygen.
Arsenic, Antimony and Bismuth Oxides
As4O6 has the same structure as P4O6, and As4O10 decays rapidly on heating to give As4O6 and oxygen.
Sb4O6 consists of molecules with the P4O6 structure in the gas and solid phases.
Bi only forms a stable oxide in the +3 oxidation state (Bi2O3). The BiVI oxide is very unstable.