The Ba₁₀S(VO₃S)₆ Oxysulfide: One-Dimensional Structure and Mixed Anion Chemical Bonding

The new oxysulfide Ba₁₀V₆S₇O₁₈, which can be written as Ba₁₀S(VO₃S)₆, was prepared by solid state reaction. It crystallizes in noncentrosymmetric space group P6₃ with the following unit cell parameters: a = 18.3018(2) Å and c = 8.6525(2) Å ( R₁ = 3.21%). This original phase exhibits (VO₃S) units separated by Ba²⁺ cations; the latter delimit one-dimensional (1D) hexagonal-like cavities filled by disordered sulfur S^2- anions and arranged into two kinds of sulfur-deficient 1D channels. Density functional theory calculations were employed to gain insights into the chemical bonding and parameters that determine the structure, particularly the V-O versus V-S bonding inside the mixed anion VO₃S tetrahedra, and the contribution of the S^2- of the cavities. The title compound can be decomposed with three components mainly interacting by ionic bonds as follows, Ba₁₀V₆S₇O₁₈ → [Ba₁₀]²⁰⁺[S]^2- [(VO₃S)₆]^18-; this description may pave the way for the design of other phases related to this system with adjusted band gap features. In particular, the effect of the V(O,S)₄:Ba ratio is discussed to emphasize the presence of the [S]^2- component, in comparison with related structures such as Ba₆V₄O₅S₁₁ [Ba₆(VO₂S₂)₂(VS₃O)(VS₄)], as it contributes strongly just below the Fermi level with subsequent alteration of the band gap.