The true nature of SmSb2O4Cl : syntheses and crystal structures of Sm2[Sb4O8]Cl2 and Eu2[Sb4O8]Cl2

Abstract

The two lanthanoid oxidoantimonate(III) chlorides SmSb2O4Cl and EuSb2O4Cl are accessible from solid‐state reactions of Sb2O3 with Ln2O3 and LnCl3 (Ln=Sm and Eu) at 750 °C for two days. They crystallize in the centrosymmetric tetragonal space group P4/ncc with the lattice parameters a=787.13(4) pm, c=1765.24(12) pm for SmSb2O4Cl and a=783.56(4) pm, c=1764.05(12) pm for EuSb2O4Cl with Z=8. Both can also be described with the crystal‐chemical formula Ln2[Sb4O8]Cl2 for Z=4, since they comprise isolated [Sb4O8]4- rings. This structural motif has some very close similarities to the known series of non‐centrosymmetric LnSb2O4Cl representatives (Ln=Gd-Lu), crystallizing in the tetragonal space group P4212. All lanthanoid(III) cations have eight oxygen atoms as nearest neighbors arranged as square prisms [LnO8]13-, which are connected to layers by four parallel edges according to ∞2{[LnO8/2e]5-} with fluorite‐like topology. The Sb3+ cations together with three oxygen atoms each and their lone‐pair of electrons form ψ1‐tetrahedra [SbO3]3-. Four of these [SbO3]3- entities join to ∞0Sb4O84- rings with four bridging and four terminal oxygen atoms. Both centrosymmetric representatives, in contrast to the series of non‐centrosymmetric ones, have a doubled lattice parameter c and several more symmetry elements, which will be discussed in detail.