The crystal structures of Er3OFS3 and Er 3of3S2: Two erbium oxide fluoride sulfides with condensed tetrahedral [ZEr4] units (Z = O and F)

Abstract

The two new compounds Er3OFS3 and Er 3OF3S2 vary mostly in their fluoride and sulfide content. The fluoride-poor erbium(III) oxide fluoride sulfide Er 3OFS3 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. (ErI)3+ is surrounded by six S2- anions in the shape of a slightly distorted octahedron, whereas (Er2) 3+ exhibits a coordination number of eight (4 x O2-7/ F- and 4 x S2- arranged as a square antiprism). In the crystal structure of Er3OFS3 edge-sharing tetrahedral [ZEr4]10'5+ units (Zn- = 50 % O2- + 50 % F-) form condensed .[OFEr2]3+ layers. These layers alternate with .[ErS3]3- sheets, built up of [ErS6]9- octahedra, which are connected through four common, edges, to complete the three-dimensional crystal structure of Er 3OFS3. 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 Zn- anions (Z = 25 % O2- + 75 % F-) in the shape of a twisted square antiprism, whereas (Er2)3+ holds a coordination number of nine (4 x O2-/F- and 5 x S2- arranged as a monocapped square antiprism), copying the arrangement around the Er3+ cations in PbFCl-type ErFS. The three-dimensional structure of Er 3OF3S2 is built up of S2- sheets and. 2[OF3Er3]4+ double layers, which are formed by strongly contorted tetrahedral [ZEr4] 10.75+ units (Zn-= 25 % O2- + 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 0/F content in the formulae, the ratio of O2-:F- is 1:1 in Er3OFS 3 and 1:3 in Er3OF3S2. © 2009 WILEYVCH Verlag GmbH & Co. KGaA.