Phosphorus pentoxide crystallizes in at atomic four forms or polymorphs. The a lot of accustomed one, a metastable form, apparent in the figure, comprises molecules of P4O10. Weak van der Waals armament authority these molecules calm in a hexagonal filigree (However, in animosity of the top agreement of the molecules, the clear packing is not a abutting packing). The anatomy of the P4O10 cage is evocative of adamantane with Td agreement point group. It is carefully accompanying to the agnate anhydride of phosphorous acid, P4O6. The closing lacks terminal oxo groups. Its body is 2.30 g/cm3. It boils at 423 °C beneath atmospheric pressure; if acrimonious added rapidly it can sublimate. This anatomy can be fabricated by abbreviating the breath of phosphorus pentoxide rapidly, the aftereffect is an acutely hygroscopic solid.
The added polymorphs are polymeric, but in anniversary case the phosphorus atoms are apprenticed by a tetrahedron of oxygen atoms, one of which forms a terminal P=O band involving the donation of the terminal oxygen p-orbital electrons to the antibonding phosphorus-oxygen individual bonds. The macromolecular anatomy can be fabricated by heating the admixture in a closed tube for several hours, and advancement the cook at a top temperature afore cooling the cook to the solid. The metastable orthorhombic, “O”-form (density 2.72 g/cm3, melting point 562 °C), adopts a layered anatomy consisting of commutual P6O6 rings, not clashing the anatomy adopted by assertive polysilicates. The abiding anatomy is a college body phase, aswell orthorhombic, the alleged O’ form. It consists of a 3-dimensional framework, body 3.5 g/cm3. The actual polymorph is a bottle or baggy form; it can be fabricated by fusing any of the others.