Fraternal Twins: Syntheses and Crystal Structures of Yb ₁₁ O ₂ (OH)[AsO ₃ ] ₈ [As ₂ O ₅ ] and Lu ₆ O[AsO ₃ ] ₄ [As ₂ O ₅ ]

The complex triclinic structure of Yb 11 O 2 (OH)[AsO 3 ] 8 [As 2 O 5 ] ( P 1; a = 843.81(6) pm, b = 841.32(6) pm, c = 1236.40(8) pm, α = 76.759(2)°, β = 71.726(2)°, γ = 85.347(2)°; Z = 1) displays eleven crystallographically different Yb 3+ cations, which are surrounded by oxygen atoms with coordination numbers ranging from six to eight. The ytterbium‐oxygen polyhedra show linkage to each other via shared corners and edges to form a network with empty channels along [100]. The [AsO 3 ] 3– and [As 2 O 5 ] 4– anions reside in these channels with their non‐binding electron pairs at their central As 3+ cations pointing toward the centers of these channels. The structure has two further special features. On the one hand, two oxygen atoms are not bonded to As 3+ cations and, together with six Yb 3+ cations, form a bitetrahedron [O 2 Yb 6 ] 14+ with a shared edge. On the other hand, there is a (OH) – group, which was created by moisture, activated from the glassy silica ampoule, and could be detected by Raman spectroscopy. The triclinic Lu 6 O[AsO 3 ] 4 [As 2 O 5 ] ( P ; a = 836.72(6) pm, b = 849.45(6) pm, c = 1344.51(9) pm, α = 81.078(2)°, β = 85.289(2)°, γ = 86.034(2)°; Z = 2) can also be described as LuAsO 3 with Z = 12 and has a similar complex structure as Yb 11 O 2 (OH)[AsO 3 ] 8 [As 2 O 5 ]. The Lu 3+ cations are surrounded by oxygen atoms showing coordination numbers of only six and seven. The six crystallographically diverse lutetium‐oxygen polyhedra also share corners and edges, erecting a network with channels along [100], in which the ψ 1 ‐tetrahedral [AsO 3 ] 3– and pyroanionic [As 2 O 5 ] 4– units are embedded. Again, their lone pairs at the As 3+ centers point into the core of these channels. This structure also contains oxygen atoms without bonds to As 3+ cations, which combine with six Lu 3+ cations to form discrete congonial bitetrahedra [O 2 Lu 6 ] 14+ .