A structural model for barium platinum oxide, Ba 3Pt 2O 7

Abstract

A single crystal study of Ba 3Pt 2O 7 shows that the structure tolerates a variable composition which can be written Ba 3Pt 2+ x O 7+2 x . The crystal studied has a hexagonal cell of dimensions a = 10.108 ± 0.006 Å and c = 8.638 ± 0.009 Å, and a probable space group P 62c, Z = 4 . The density determined by water displacement is 7.99 g/cm 3; the theoretical density for Ba 3Pt 2O 7 is 7.94 g/cm 3. The structure was determined from the set of 401 observed independent reflections obtained from 5189 reflections measured by automated counter methods. Refinement on F was carried to a conventional R of 8.0%. The structure has barium-oxygen layers with an essentially four-layer stacking sequence of the double hexagonal (ABAB) type. Platinum is found mainly in face-sharing octahedra, but is also distributed over some sites in which the coordination is nearly square planar and other sites in which the coordination is trigonal prismatic with three PtO bond lengths of 2.00 Å and three long PtO distances of 2.65 Å. The platinum with planar coordination is 0.08 Å from the plane of the four oxygen atoms.