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 P6(3) with the following unit cell parameters: a = 18.3018(2) angstrom and c = 8.6525(2) angstrom (R-1 = 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 S2- 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 S2- of the cavities. The title compound can be decomposed with three components mainly interacting by ionic bonds as follows, Ba10V6S7O18 -> [Ba-10](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 [Ba-6(VO2S2)(2)(VS3O)(VS4)], as it contributes strongly just below the Fermi level with subsequent alteration of the band gap.