Dy2Te3O9: Der erste Vertreter von Lanthanoid(III)-Oxotelluraten der Zusammensetzung M2Te3O9†

Dy2Te3O9: The First Representative of Lanthanoid(III)-Oxotellurates(IV) with the Composition M2Te3O9 Single crystals of Dy2Te3O9 could be obtained by reaction of Dy2O3 with TeO2 in a 1 : 4 molar ratio as first representative of the formula type M2Te3O9. In this oxotellurate(IV), the lanthanoid(III) cations are hepta- (capped trigonal prism: Dy4) and octacoordinated (bicapped trigonal prisms: Dy1–Dy3) by oxygen atoms, respectively. These dysprosium–oxygen polyhedra build up layers parallel to the (100) plane by sharing common edges as dominating feature of the crystal structure. Because of the proportionally higher Dy2O3 moiety in Dy2Te3O9 (Dy2O3 : TeO2 =1 : 3), these ∞2{[Dy4O17]22–} sheets appear more bulky and corrugated than the almost planar ∞2{[Dy2O11]16–} layers in Dy2Te4O11 (Dy2O3 : TeO2 = 1 : 4). In spite of its rather complex constitution, the tellurium–oxygen partial structure in Dy2Te3O9 shows remarkably different motifs. The six crystallographically independent Te4+ cations are each surrounded by three oxygen atoms, which form together with the lone-pair electrons [TeO3]2– ions of ψ1-tetrahedral shape. However, three of them show higher coordination numbers such as CN = 3+3 (Te1) and CN = 3+2 (Te2 and Te3) by strong secondary Te···O interactions with adjacent oxotellurate(IV) units, whilst the other three (Te4–Te6: CN = 3) have no secondary contacts at all. The typical 3+1-coordination of Te4+ as in Dy2Te4O11 and generally common in other rare-earth metal(III) oxotellurates(IV) does not occur. Also oxoditellurate(IV) units ([Te2O5]2–) as in Dy2Te4O11 or even more condensed ones ([Te3O8]4–) as in Dy2Te5O13 cannot be observed in Dy2Te3O9, owing to its proportionally smaller TeO2 moiety. Five of the [TeO3]2– ions group to screw-like strands along the [010] direction according to ∞1{[Te5O15]10–} through strong secondary Te···O contacts, whereas the remaining [(Te6)O3]2– units reside isolated within channelsof the porous ∞2{[Dy4O17]22–} sheets. The linkage of the ∞2{[Dy4O17]22–} partial structure to achieve a framework only takes place by [(Te4)O3]2– ions through Dy3–O–Te4–O–Dy4 bridges. Between the ∞2{[Dy4O17]22–} layers as well as within their channels there is still enough space left to accommodate the stereochemically active lone-pair electrons at the Te4+ ions.