Abstract
Crystals of the new compound, AgSr4Cu4.5(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.
Highlights
Crystals of the new compound, AgSr4Cu4.5(PO4)6, were grown successfully by the hydrothermal 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 crystal-structure cohesion is ensured by ionic bonds between the silver and strontium cations and the oxygen anions belonging to two adjacent sheets
Summary
The growing role of metal orthophosphates based on PO4 and MOn (where M is a metal cation) structural units is closely related to their ability to adopt different spatial arrangements. The ability of these metal cations to adopt different oxidation states as well as various coordination environments leads, in general, to open anionic three-dimensional frameworks. The structures of these classes of materials can accommodate a great variety of substituents, anionic and/or cationic, which can have a significant effect on the stability and on the morphology of structures and crystals, as is shown in the apatite family (LeGeros & Tung, 1983) for which a considerable number of complex and versatile networks were described systematically. A careful examination of the literature as well as various databases reveals that the title compound AgSr4Cu4.5(PO4) is original and is not related to any family of reported compounds
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