Oxotellurate(IV) der Lanthanide: II. Die isotype Reihe M₂Te₅O₁₃ (M = Dy – Lu) / Oxotellurates(IV) of Lanthanides: II. The Isotypic Series M₂Te₅O₁₃ (M = Dy – Lu)

For the shortly discovered formula type M₂Te₅O₁₃ (triclinic, P1̄), the establishment of an isostructural series in the last third of the lanthanide family (M = Dy - Lu) was possible. The excessive formula unit TeO₂ additional to the well-known composition M₂Te₄O₁₁ (monoclinic, C2/c) leads to the slicing of the [M₂O₁₀]¹⁴⁻ layers which are typical for the tellurium-oxide poorer compounds. By coupling together the bicapped trigonal prismatic (M1, CN = 8) and the pentagonal bipyramidal (M2, CN = 7) lanthanide-oxygen polyhedra via edges, [M₄O₂₀]²⁸⁻ bands are formed stretching along the a axis and piling up to a primitive rod-packing. The linkage of these bands occurs parallel to the (010) plane via Te3 as well as via Te4 parallel to (100). Besides the usual 3+1 coordination, two of the five crystallographically independent tellurium sites are coordinated regularly fourfold (d(Te−O) ≈ 186−213 pm) and even 3+2-fold by oxygen atoms. The tellurium-oxygen polyhedra form corrugated layers running parallel to (101) which follow so close to each other that the tellurium-oxygen partial structure appears to be almost three-dimensional at a passing glance. As in M₂Te₄O₁₁-type representatives, the non-bonding electron pair (lone pair) of each Te⁴⁺ cation shows stereochemical activity which always appears to flock together in large tellurium neighboured positions.