Triply-linked phosphate

The evidence for cross-linking in crystalline inorganic polyphosphates to convert them to crystalline ultraphosphates with small degrees of cross-linking is circumstantial rather than direct. This is not to question the triply-linked phosphate groups in the... 

Condensed phosphates in which at least some of the PO4 tetrahedra share three comer O atoms are called ultraphosphates. In contrast to structures which involve only doubly linked tetrahedra (i.e. polyphosphates and metaphosphates), most ultraphosphates hydrolyse extranely rapidly in contact with moisture. This instability is usually associated with the triply linked tetrahedra and may arise because energy from resonance stabilisation is lacking. 

Next, a line between poly- and ultraphosphates represents metaphosphate compositions. These are long-chain polyphosphates or ring compounds. Both types have been discovered and this line is very important for preparations of phosphate fibers. Above metaphosphate compositions are ultraphosphates. These are rich in P2O5 and all compositions in this area contain cross-linked phosphates, or triply... 

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