LnSb2O4Br (Ln=Nd and Er) and Sb4O5Br2: Lanthanoid‐Bearing and ‐Free Antimony(III) Oxide Bromides

Sb4O5Br2 crystallizes plate‐shaped in the monoclinic space group P21/c with the lattice parameters a=660.82(5) pm, b=513.71(4) pm, c=1346.35(9) pm and β=97.876(3)° for Z=2. Its crystal structure contains {[Sb4O5]2+} layers with connected [(Sb1)O3+1]5− ψ1‐units and undisturbed pyramidal [(Sb2)O3]3− ψ1‐units, where the free electron pair is counted as a pseudo‐ligand (ψ). The bromide anions required for charge compensation of these cationic {[Sb4O5]2+} layers form single sheets and are only bonded via van‐der‐Waals interactions in this crystal structure, as the nearest distance to antimony cations is at least 300 pm. NdSb2O4Br crystallizes plate‐shaped in the monoclinic space group P21/c as well, but with the lattice parameters a=896.24(6) pm, b=801.16(5) pm, c=799.27(5) pm and β=92.129(3)° for Z=4. The [NdO8]13− polyhedra are linked to each other via four edges and thus form fluorite‐related layers {[NdO ]5−}, which run parallel to the (100) plane. The [SbO3]3− anions share vertices to build chains {[SbO O ]−} along [001], which align parallel within the (100) plane. The isolated Br− anions arrange in layers and show a minimum distance of 319 pm to the next Sb3+ cation. ErSb2O4Br crystallizes plate‐shaped in the non‐centrosymmetric tetragonal space group P4212 with the lattice parameters a=774.76(4) pm, c=899.53(6) pm and c/a=1.161 for Z=4. The erbium‐oxygen environment appears to be roughly the same as in NdSb2O4Br, so the main difference is the linkage of the ψ1‐[SbO3]3− units. Four of these [SbO3]3− anions assemble in a ring structure {[Sb4O8]4−} by sharing corners. Layers of rings are located in the (001) plane and almost planar bromide‐anion slabs assemble between the antimony‐oxygen layers. In this article, all three crystal structures are compared with each other and single‐crystal Raman spectra were recorded and analyzed for NdSb2O4Br and ErSb2O4Br.