Preparation and structural elucidation of the new anion-excess fluorite variant Ba4Er3F17

Pink coloured crystals of the new complex fluoride Ba4Er3F17 were prepared via solid state reactions from mixed powders of BaF2 and ErF3 (4: 3) in pla tinum crucibles under Ar (1973 K, 48 h). Ba4Er3F17 crystallizes in the spac e group R (3) over barm with a = 11.059(1) and c = 20.346(2) Angstrom. The structural parameters have been refined using single crystal data. The stru cture of Ba4Er3F17 can be described as an ordered anion-rich fluorite type structure. The excess fluorine content is directly correlated with the occu rence of Er6F36 clusters. Within these units the central F-12 cuboctahedra are centered by one additional F which lies on a sixfold split position. Th e trivalent Er are square antiprismatically surrounded by 8 F with distance s Er-F ranging from 2.24 to 2.44 Angstrom and an additional capping F at 2. 59 Angstrom. The two crystallographically different Ba are coordinated by 1 0 and 11 F, respectively, at distances of 2.59-3.15 Angstrom. Calculations of the Madelung part of the lattice energy, MAPLE, were performed for the a nalysis of the chemical bonding. (C) 2001 Editions scientifiques et medical es Elsevier SAS. All rights reserved.