The type IV polymorph of KEu(PO3)4

Single crystals of KEu(PO(3))(4), potassium europium(III) polyphosphate, were obtained by solid-state reactions. This monoclinic form is the second polymorph described for this composition and belongs to type IV of long-chain polyphosphates with general formula A(I)B(III)(PO(3))(4). It is isotypic with its KEr(PO(3))(4) and KDy(PO(3))(4) homologues. The crystal structure is built of infinite helical chains of corner-sharing PO(4) tetra-hedra with a repeating unit of eight tetra-hedra. These chains are further linked by isolated EuO(8) square anti-prisms, forming a three-dimensional framework. The K(+) ions are located in pseudo-hexa-gonal channels running along [01] and are surrounded by nine O atoms in a distorted environment.