Versatile Interplay of Chalcogenide and Dichalcogenide Anions in the Thiovanadate BaS(VSO)(S) and Its Selenide Derivatives: Elaboration and DFT Meta-GGA Study.

Oxychalcogenides are emerging as promising alternative candidates for a variety of applications including for energy. Only few phases among them show the presence of Q-Q bonds (Q = chalcogenide anion) while they drastically alter the electronic structure and allow further structural flexibility. Four original oxy(poly)chalcogenide compounds in the system Ba-V-Q-O (Q = S, Se) were synthesized, characterized, and studied using density functional theory (DFT). The new structure type found for BaVOS, which can be written as BaS(VSO)(S), was substituted to yield three selenide derivatives BaVOSSe, BaVOSSe, and BaVOSSe. They represent original multiple-anion lattices and first members in the system Ba-V-Se-S-O. They exhibit in the first layer heteroleptic tetrahedra VSO and isolated Q anions and in the second layer dichalcogenide pairs (Q) with Q = S or Se. Selenide derivatives were attempted by targeting the selective substitution of isolated Q or (Q) (in distinct layers) or both by selenide, but it systematically led to concomitant and partial substitution of both sites. A DFT meta-GGA study showed that selective substitution yields local constraints due to rigid VOS and pairs. Experimentally, incorporation of selenide in both layers avoids geometrical mismatch and constraints. In such systems, we show that the interplay between the O/S anionic ratio around V, together with the presence/nature of the dichalcogenides (Q) and isolated Q, impacts in unique manners the band gap and provides a rich background to tune the band gap and the symmetry.