Superstructures and Chemical Bonding in Rare Earth Metal Polytellurides RETe2‐δ (RE=La−Nd; Sm−Tm; 0≤δ≤0.2)

Polychalcogenides REX 2‐δ ( X =S, Se, Te; 0≤ δ ≤0.2) of trivalent rare earth metals RE have been investigated in recent years to shed light on the structural diversity as a function of compositional, metric, thermodynamic, and electronic situation. Whereas the former aspects have comparable influence on the structures of all polychalcogenides REX 2‐δ , the bonding situation was assumed different for tellurides due to tellurium's higher tendency to delocalize electrons. The crystal structures generally contain puckered [ REX ] double slabs and planar [ X ] layers, the latter hosting different distortions from a square‐like arrangement. The distortion patterns of sulfides and selenides can be understood by a Zintl‐type approach; they are dominated by localization of valence electrons in mono‐ ( X 2− ) or dinuclear ( X 2 2− ) anions only. This review discusses crystal structures of some rare‐earth metal polytellurides RE Te 2‐δ (0≤ δ ≤0.2) and bonding features in the chalcogenide layers and relates them to their sulfide and selenide counterparts.