The Crystal Structure of Ba5Cu2Al3F23: A Complex Barium, Copper, Aluminum Fluoride, with Copper (II) in Trigonal Prismatic Environment

Ba5Cu2Al3F23 is monoclinic: a=28.44(2) ?, b=7.322(4) ?, c=27.95(2) ?, BETA =108.95(3)°, Z=12. The crystal structure was solved in the space group P21/c (no. 14), from X-ray single crystal data using 14,235 unique reflections (5307 with Fo/SIGMA(Fo)>4). It is built up from a complex tridimensional arrangement of [MF6] octahedra (M=Al3+ and/or Cu2+) and [CuF6] trigonal prisms, which form infinite tilted cis chains running perpendicular to the bc plane of the cell. Each chain is connected, roughly in the c direction, to four others, two up and two down, by octahedra vertices. The barium ions, 12- and 13-coordinated to fluorine atoms, ensure the electroneutrality of the structure. They are inserted between the chains.