A Group‐Subgroup Relationship Between the New Nitride Tellurides of Terbium and Dysprosium with the Composition M 4 N 2 Te 3

Two new non ‐isostructural lanthanide(III) nitride tellurides with the composition M 4 N 2 Te 3 bearing terbium (Tb 4 N 2 Te 3 ) and dysprosium (Dy 4 N 2 Te 3 ) could be synthesized by the reaction of terbium (Tb) or dysprosium (Dy) metal with sodium azide (NaN 3 ), tellurium (Te), iodine (I 2 ), and sodium iodide (NaI) as flux in evacuated silica tubes for seven days at 950 °C. Tb 4 N 2 Te 3 crystallizes orthorhombically in space group Pnna with the lattice parameters a = 727.14(5), b = 1164.37(8), c = 1100.93(7) pm, V m = 140.33(2) cm 3 · mol –1 ( Z = 4). In contrast, Dy 4 N 2 Te 3 appears in the monoclinic space group P 2 1 / n with the lattice parameters a = 719.56(5), b = 1164.05(8), c = 1097.34(7) pm, β = 91.327(3)°, V m = 138.34(2) cm 3 · mol –1 ( Z = 4). Corresponding to the lanthanide contraction the cell parameters of Dy 4 N 2 Te 3 show slightly smaller values compared to Tb 4 N 2 Te 3 , but the change of symmetry leads to a different crystal system. Symmetry operations related to a and c are lost according to P 2/ n 2 1 / n 2/ a → P 12 1 / n 1 and the two crystallographically independent M 3+ cations in Tb 4 N 2 Te 3 split into four in Dy 4 N 2 Te 3 . Both Tb 3+ cations are coordinated by six anions in first sphere plus one Te 2– anion further apart for (Tb1) 3+ leading to capped trigonal prisms and distorted octahedra. The four Dy 3+ cations with coordination numbers of six plus one and three times six also reside in capped and uncapped distorted octahedral anionic coordination. Both crystal structures have infinite zigzag chains in 1 ∞ {[N M $\rm^{e}_{4/2}$ ] 3+ } in common, which are formed by trans ‐edge connected [N M 4 ] 9+ tetrahedra. They run along [010] and exhibit two crystallographically different N 3– anions in both cases. The latter are coordinated on the one hand to two sorts of Tb 3+ cations in Tb 4 N 2 Te 3 and on the other hand to four sorts of Dy 3+ cations in Dy 4 N 2 Te 3 as major structural difference. However, both crystal structures show a clear group‐subgroup relationship.