The development of cyclophosphate crystal chemistry

Among the various condensation schemes occurring in phosphoric anions one of them leads to the formation of cyclic entities. The corresponding salts, for a long time called “metaphosphates” are now denominated cyclophosphates.Built up by a ring of corner-sharing PO4 tetrahedra, the general formula of their anions is PnO3nn−. Today these anions are known for n=3, 4, 5, 6, 8, 9, 10, and 12. The development of the chemistry of cyclophosphates was very slow, spreading along almost two centuries. We report first a short history of the development of each class of cyclophosphates, then we examine their general properties