PREPARATION, PROPERTIES, AND CRYSTAL-STRUCTURES OF TI3ZN22 AND TIZN16

Single crystals of Ti3Zn22 and TiZn16 were isolated from slowly cooled zinc-rich samples by dissolving their matrices in hydrochloric acid, which attacks the titanium-containing crystals at a lower rate. Both compounds are Pauli paramagnetic and show metallic conductivity. Their crystal structures were determined from single-crystal X-ray data. Ti3Zn22 is of a new structure type with tetragonal symmetry: P4(2)/mbc, a = 1152.3(1), c = 1145.6(2) pm, Z = 4, R = 0.020 for 920 structure factors and 64 variable parameters. The titanium atoms occupy two different sites with the coordination numbers 15 and 16, respectively, and one titanium position shows mixed occupancy, which results in the exact composition Ti-2.841(8)Zn-22.159(8). The seven different zinc atoms have between 11 and 14 near neighbors. The previously reported structure of TiZn16 is confirmed: Cmcm, a = 769.9(3), b = 1141.4(4), c = 1180.0(3) pm, Z 4, R = 0.022 for 787 structure factors and 50 variables. Both structures can be described as packings of different atomic layers. These layers are densely populated by zinc atoms or less densely populated by both titanium and zinc atoms. Both structures contain relatively large voids and it is suggested that these voids are filled with nonbonding electrons of the zinc atoms. (C) 1995 Academic Press, Inc.