The structure of onoratoite, Sb₈ O₁₁ X₂ (X = Cl, Br) revisited

The crystal structure of Sb₈O₁₁Cl₂ (onoratoite) is redetermined in the triclinic space group P-1. The crystal structure was previously described by a partially disordered model in the monoclinic space group C 2 / m containing some partially occupied oxygen atoms. The new structural model features exclusively atomic positions that are fully occupied. The crystal structure was solved from single crystal data and the unit cell parameters are a = 10.317 (2)  Å, b = 11.269 (2)  Å, c = 13.939 (3)  Å, α = 79.29 (2) °, β = 76.29 (2) °, γ = 73.00 (2) °, Z = 2, R = 0.0637. It contains antimony oxide in the form of infinite tubes interleaved with halide ions, a main feature very similar to the previous model. However, in the new model the tubes contain both [SbO₄E] (E = 5s² lone pair of electrons) trigonal bipyramids and [SbO₃E] tetrahedral, whereas the old model was composed entirely of trigonal bipyramidal [SbO₄E] units. The isostructural compound Sb₈O₁₁Br₂ was synthesized as well.