Versatile Interplay of Chalcogenide and Dichalcogenide Anions in the Thiovanadate Ba 7 S(VS 3 O) 2 (S 2 ) 3 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 Ba 7 V 2 O 2 S 13 , which can be written as Ba 7 S(VS 3 O) 2 (S 2 ) 3 , was substituted to yield three selenide derivatives Ba 7 V 2 O 2 S 9.304 Se 3.696 , Ba 7 V 2 O 2 S 7.15 Se 5.85 , and Ba 7 V 2 O 2 S 6.85 Se 6.15 . 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 V 5+ S 3 O and isolated Q 2- anions and in the second layer dichalcogenide pairs (Q 2 ) 2- with Q = S or Se. Selenide derivatives were attempted by targeting the selective substitution of isolated Q 2- or (Q 2 ) 2- (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 VO 3 S 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 5+ , together with the presence/nature of the dichalcogenides (Q 2 ) 2- and isolated Q 2- , impacts in unique manners the band gap and provides a rich background to tune the band gap and the symmetry.