title: Synthesis and crystal structure of a series of incommensurately modulated composite oxohalide compounds.
abstract: Transparent, needle-like single crystals of the isostructural compounds [Sb4O7+3δX4][Zn3]1+δ (X = Cl, Br, I) δ ≈ 0.2 were obtained from chemical reactions in evacuated and sealed silica tubes. First, the average structure was solved in P21/n but the model refined poorly and a lowering of the symmetry to the 3 + 1 dimensional space group P21(α0γ)0 gave a significantly better fit to the data. This model used second order positional modulations for all the atoms. Whereas Sb, Cl (Br, I) and most O positions were well behaved, there was a mismatch with Zn that was better described in a sub-cell, thus yielding a composite structure. The composite nature of the structure leads to a charge imbalance that is compensated by oxygen vacancies.
authors.affiliation: Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden. mats.johnsson@mmk.su.se.
authors.forename: Iwan
authors.initials: I
authors.lastname: Zimmermann
authors.forename: Alexis
authors.initials: A
authors.lastname: Corgnet
authors.forename: Mats
authors.initials: M
authors.lastname: Johnsson
authors.forename: Sven
authors.initials: S
authors.lastname: Lidin