Low temperature crystal growth and structure of ordered Ba7F12Cl2

Crystals of composition Ba7F12Cl2 were obtained by a reaction at room tempe rature between Ba2+/Cl-/F- in a gel of agar-agar/water. The hexagonal cryst als have space group P (6) over bar, a = 1064.69(8), c = 417.89(5)pm, V = 4 10.24(5) 10(6) pm(3) and Z = 1. The anions form a propeller type network lo cated in tunnels parallel to the c(hex) axis; the chloride ions are located at the center on the propeller axes. The Ba2+ ions are coordinated by a (d istorted) tricapped trigonal environment of fluoride and chloride anions. D isorder is present for one particular Ba2+ site. The average structure is i sotypic with the structure of Pb7F12Cl2.