Renaissance of the stella quadrangula. The lanthanoid nitride tellurides Ln₁₃N₅Te₁₂ (Ln = La-Nd)

Ln₁₃N₅Te₁₂ (Ln = La-Nd), a quite unusual composition of the lanthanoid(III) nitride tellurides, appears with a new crystal structure and can be obtained by reactions of lanthanoid metal (Ln) with elemental tellurium (Te), sodium azide (NaN₃), elemental iodine (I₂) and sodium iodide (NaI) as flux in evacuated fused silica tubes for seven days at 900 C. The black, shard-shaped single crystals of the short new series Ln₁₃N₅Te₁₂ (Ln = La-Nd) crystallize monoclinically in the space group P2₁/m with lattice parameters ranging from a = 1039.86(7), b = 1373.29(9), c = 1311.78(9) pm, β = 100.103(3) for La₁₃N₅Te₁₂ to a = 1016.73(7), b = 1337.58(9), c = 1288.92(9) pm, β = 100.094(3) for Nd₁₃N₅Te₁₂ and Z = 2. Unlike the other ternary compounds of the lanthanoid(III) nitride tellurides, two different types of isolated oligomers containing edge-sharing [NLn₄]⁹⁺ tetrahedra occur in their crystal structure. The fusion of two [NLn₄]⁹⁺ units via one common edge forms [N₂Ln₆]¹²⁺ bitetrahedra, which are already known from the Ln₃NTe₃ examples with Ln = Gd-Ho. In contrast, the [N₃Ln₇]¹²⁺ trimers built up by three [NLn₄]⁹⁺ tetrahedra with two sharing edges for each [NLn₄]⁹⁺ unit, but three common edges overall, represent a new highlight. Both kinds of oligomers can be traced back to a stella quadrangula [N₄Ln₈]¹²⁺ and are embedded in a dense matrix of Te^2- anions according to {[Ln₆N₂][Ln₇N₃]Te₁₂}. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)