Crystal structure of silver strontium copper orthophosphate, AgSr₄Cu_4.5(PO₄)₆

Crystals of the new compound, AgSr₄Cu_4.5(PO₄)₆, were grown successfully by the hydro-thermal process. The asymmetric unit of the crystal structure of the title compound contains 40 independent atoms (4 Sr, 4.5 Cu, 1 Ag, 6 P and 24 O), which are all in general positions except for one Cu atom, which is located on an inversion centre. The Cu atoms are arranged in CuO _n (n = 4 or 5) polyhedra, linked through common oxygen corners to build a rigid three-dimensional motif. The connection of these copper units is assured by PO₄ tetra-hedra. This arrangement allows the construction of layers extending parallel to the (100) plane and hosts suitable cavities in which Ag⁺ and Sr²⁺ cations are located. The crystal-structure cohesion is ensured by ionic bonds between the silver and strontium cations and the oxygen anions belonging to two adjacent sheets. Charge-distribution analysis and bond-valence-sum calculations were used to validate the structural model.