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

Abstract Ba 5 Cu 2 Al 3 F 23 is monoclinic: a =28.44(2) A, b =7.322(4) A, c =27.95(2) A, β =108.95(3)°, Z =12. The crystal structure was solved in the space group P 2 1 / c (no. 14), from X-ray single crystal data using 14,235 unique reflections (5307 with F o / σ ( F o )>4). It is built up from a complex tridimensional arrangement of [ M F 6 ] octahedra ( M =Al 3+ and/or Cu 2+ ) and [CuF 6 ] 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.