The Crystal Structures of Er₃OFS₃ and Er₃OF₃S₂: Two Erbium Oxide Fluoride Sulfides with Condensed Tetrahedral [ZEr₄] Units (Z = O and F)

The two new compounds Er₃OFS₃ and Er₃OF₃S₂ vary mostly in their fluoride and sulfide content. The fluoride‐poor erbium(III) oxide fluoride sulfide Er₃OFS₃ crystallizes in the tetragonal space group I4/mmm (a = 374.86(2), c = 2068.41(9) pm, Z = 2) with two crystallographically different Er³⁺ cations. (Er1)³⁺ is surrounded by six S^2– anions in the shape of a slightly distorted octahedron, whereas (Er2)³⁺ exhibits a coordination number of eight (4 × O^2–/F^– and 4 × S^2– arranged as a square antiprism). In the crystal structure of Er₃OFS₃ edge‐sharing tetrahedral [ZEr₄]^10.5+ units (Z^n– = 50 % O^2– + 50 % F^–) form condensed {}^2_\infty[OFEr₂]³⁺ layers. These layers alternate with {}^2_\infty[ErS₃]^3– sheets, built up of [ErS₆]^9– octahedra, which are connected through four common edges, to complete the three‐dimensional crystal structure of Er₃OFS₃. The fluoride‐rich erbium(III) oxide fluoride sulfide Er₃OF₃S₂ crystallizes in the orthorhombic space group Ccce (a = 538.31(2), b = 1892.03(9), c = 538.27(2) pm, Z = 4). Two crystallographically distinct Er³⁺ cations are present in its crystal structure. (Er1)³⁺ is surrounded by eight Z^n– anions (Z = 25 % O^2– + 75 % F^–) in the shape of a twisted square antiprism, whereas (Er2)³⁺ holds a coordination number of nine (4 × O^2–/F^– and 5 × S^2– arranged as a monocapped square antiprism), copying the arrangement around the Er³⁺ cations in PbFCl‐type ErFS. The three‐dimensional structure of Er₃OF₃S₂ is built up of S^2– sheets and {}^2_\infty[OF₃Er₃]⁴⁺ double layers, which are formed by strongly contorted tetrahedral [ZEr₄]^10.75+ units (Z^n– = 25 % O^2– + 75 % F^–). The crystals of this compound show a prominent superstructure in the tetragonal space group I4/mmm with a = 380.59(3), c = 1892.03(9) pm and Z = 2. In the crystal structures of both title compounds, the light anions O^2– and F^– occupy one crystallographically unique Wyckoff position in a statistic allocation. Subject to the O/F content in the formulae, the ratio of O^2–:F^– is 1:1 in Er₃OFS₃ and 1:3 in Er₃OF₃S₂.