X-RAY STRUCTURE DETERMINATION OF PSEUDOMEROHEDRALLY TWINNED COGE1.5S1.5 AND COGE1.5SE1.5, ABSORPTION CORRECTION

The crystal structures of the mixed skutterudites CoGe1.5S1.5 and CoGe 1.5Se1.5 were determined by X-ray diffraction of powder samples and ps eudomerohedral multiple twins (space group R3, No. 146, Z = 24, CoGe1. 5S1.5: a = 1133.63(10) pm, c = 1391.76(9) pm, R(F)= 2.2%, 4288 unique reflections; CoGe1.5Se1.5: a = 1173.00(8) pm, c = 1441.1(3) pm, R(F) = 2.8%, 828 unique reflections). The triple pseudomerohedral twins are connected by three twofold rotation axes, which are linked by a threef old rotation axis. An absorption correction was performed by an intens ity and volume ratio weighted empirical method. The intensity data for CoGe1.5Se1.5 were collected in two different azimuth and theta positi ons in order to minimise the absorption effects. The structures obtain ed are compared with those of binary skutterudites with respect to sym metry relations of the space groups and bonding of the rhombic Ge(2)X( 2) units (X = S, Se), which partly reveal antiaromatic 4 pi electron b ehavior.