title: Substitutional and positional disorder in Sr(2.88)Cu(3.12)(PO4)4.
abstract: The title compound, a hydrothermally synthesized strontium copper(II) phosphate(V) (2.88/3.12/4), is isotypic with Sr(3)Cu(3)(PO(4))(4), obtained previously by solid-state reaction, but not with Sr(3)Cu(3)(PO(4))(4), obtained previously by the hydrothermal method. A surplus of copper was observed by both structural and chemical analysis, and the formula obtained by the structural analysis is in full agreement with results of the EDX (energy-dispersive X-ray diffraction) analysis. The structure consists of layers of Cu(3)O(12) groups which are linked via the PO(4) tetrahedra. The Cu(3)O(12) groups are formed by one Cu1O(4) and two Cu2O(5) coordination polyhedra sharing corners. The central Cu1 atom of the Cu(3)O(12) group is located at an inversion centre (special position 2a). The unique structural feature of the title compound is the presence of 12% Cu in the Sr1 site (special position 2b, site symmetry 1). Moreover, disordered Sr2 atoms were observed: a main site (Sr2a, 90%) and a less occupied site (Sr2b, 10%) are displaced by 0.48 (3) A along the b axis. Such substitutional and positional disorder was not observed previously in similar compounds.
authors.affiliation: Faculty of Mining and Geology, University of Belgrade, Dusina 7, 11000 Belgrade, Serbia. ljika2002@yahoo.com
authors.forename: Ljiljana
authors.initials: L
authors.lastname: Karanović
authors.forename: Sabina
authors.initials: S
authors.lastname: Sutović
authors.forename: Dejan
authors.initials: D
authors.lastname: Poleti
authors.forename: Tamara
authors.initials: T
authors.lastname: Dordević
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Pacevski