SYNTHESIS AND STRUCTURE OF BA6MG7F26

A new compound in the binary phase diagram of BaF2 and MgF2 was synthe sized. After Czrochalsky growth of BaMgF4, needle shaped crystals were found on the surface of the cooled residual mass. The compound Ba6Mg7 F26 crystallizes in the orthorhombic space group Immm with lattice par ameters of a=585.35(4), b=1214.95(7), and c=1511.09(9) pm. The global structure can be described as build up of perovskite like blocks and r utile related parts. Magnesium ions have an octahedral fluoride enviro nment with minimum (maximum) bond distances of 192.1(2) (227.4(3)) pm. Two different barium environments with coordination number (C.N.) of 12 + 1 (Ba1) and 12 (Ba2) were found. The different fluoride ions can have C.N. of 6, 4 or 3 with the nearest metal atoms. Preliminary Raman spectra show significant differences between BaMgF4 and Ba6Mg7F26.