The BaS(VOS) Oxysulfide: One-Dimensional Structure and Mixed Anion Chemical Bonding.

The new oxysulfide BaVSO, which can be written as BaS(VOS), was prepared by solid state reaction. It crystallizes in noncentrosymmetric space group P6 with the following unit cell parameters: a = 18.3018(2) Å and c = 8.6525(2) Å ( R = 3.21%). This original phase exhibits (VOS) units separated by Ba cations; the latter delimit one-dimensional (1D) hexagonal-like cavities filled by disordered sulfur S 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 VOS tetrahedra, and the contribution of the S of the cavities. The title compound can be decomposed with three components mainly interacting by ionic bonds as follows, BaVSO → [Ba][S] [(VOS)]; 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):Ba ratio is discussed to emphasize the presence of the [S] component, in comparison with related structures such as BaVOS [Ba(VOS)(VSO)(VS)], as it contributes strongly just below the Fermi level with subsequent alteration of the band gap.