Apatite-type SrPr4(SiO4)3O

Single crystals of the title compound, strontium tetra-praseo-dymium tris-(silicate) oxide, SrPr(4)(SiO(4))(3)O, have been grown by the self-flux method using SrCl(2). The structure is isotypic with the apatite supergroup family having the generic formula (IX)M1(2) (VII)M2(3)((IV)TO(4))(3)X, where M = alkaline earth and rare earth metals, T = Si and X = O. The M1 site (3.. symmetry) is occupied by Pr and Sr atoms with almost even proportions and is surrounded by nine O atoms forming a tricapped trigonal prism. The M2 site (m.. symmetry) is almost exclusively occupied by Pr and surrounded by seven O atoms, forming a distorted penta-gonal bipyramid. The Si atom (m.. symmetry) is surrounded by two O (m.. symmetry) and two O atoms in general positions, forming an isolated SiO(4) tetra-hedron. Another O atom at the inversion centre (.. symmetry) is surrounded by three M2 sites, forming an equilateral triangle perpendicular to the c axis.