Ternäre Thallium-Übergangsmetall-Chalkogenide mit ThCr2Si2-Struktur

The existence of ternary chalcogenides of general composition TlT ₂ X ₂ (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.