TERNARY THALLIUM TRANSITION-METAL CHALCOGENIDES WITH THCR2SI2-STRUCTURE

The existence of ternary chalcogenides of general composition Tl T2X2 (T=Fe,Co,Ni, X=S;T=Fe,Co,Ni,Cu, X=Se) crystallizing in the ThCr2Si2-structure type has been established. The crystal structure of TlCo2S2 was refined from single crystal diffractometer data. The dimensions of the tetragonal unit cells are: TlFe2S2;a=3.755 (1), c=13.35 (1) Å; TlCo2S2:a= =3.7410 (5), c=12.956(5) Å; TlNi2S2:a=3.792 (1), c=12.77 (1) Å; TlFe2Se2:a=3.890 (1), c=14.00(1) Å; TlCo2Se2:a=3.847 (1), c=13.54 (1) Å; TlNi2Se2:a=3.866 (1), c=13.41 (1) Å; TlCu2Se2:a=3.852 (1), c=14.01 (1) Å. These phases are the first chalcogenides found to crystallize in the ThCr2Si2-structure type. Unlike the already known representatives of this structure type they show a pronounced partial ionic character. Interatomic distances as well as the relations to the alkali thiometallates of Co and Mn are discussed. © 1978 Springer-Verlag.