Y16I19C8B4 - A YTTRIUM BORIDE CARBIDE HALIDE CONTAINING B2C4 UNITS

The new compound Y16I19C8B4 was prepared from Y, YI3, C and B at 1050- 1150 degrees C. The structure of a twinned crystal was determined by m eans of X-ray diffraction (space group P(1) over bar $, a = 12.311(2) Angstrom, b = 13.996(3) Angstrom, c = 19.695(3) Angstrom, alpha = 74.9 6(2)degrees, beta = 89.51(2)degrees, gamma = 67.03(2)degrees, Z = 2). Y16I19C8B4 is a semiconductor and contains nearly planar B2C4 units wh ich are located in cages built up by 12 yttrium atoms. Assuming (B2C4) (12-), these units can be regarded as isoelectronic with B2F4. The ytt rium cages are connected via faces to form rods, which are surrounded by iodine atoms. Bridging iodine atoms connect the rods so that layers are formed. The characteristic twinning observed can be understood fr om the geometry of the crystal structure.