Versatile Interplay of Chalcogenide and Dichalcogenide Anions in the Thiovanadate Ba7S(VS3O)2(S2)3 and Its Selenide Derivatives: Elaboration and DFT Meta-GGA Study

Oxychalcogenides are emerging as promising alternativecandidatesfor a variety of applications including for energy. Only few phasesamong them show the presence of Q-Q bonds (Q = chalcogenideanion) while they drastically alter the electronic structure and allowfurther structural flexibility. Four original oxy-(poly)-chalcogenidecompounds in the system Ba-V-Q-O (Q = S, Se)were synthesized, characterized, and studied using density functionaltheory (DFT). The new structure type found for Ba7V2O2S13, which can be written as Ba7S-(VS3O)(2)(S-2)(3),was substituted to yield three selenide derivatives Ba7V2O2S9.304Se3.696, Ba7V2O2S7.15Se5.85, and Ba7V2O2S6.85Se6.15. They represent original multiple-anion lattices and firstmembers in the system Ba-V-Se-S-O. Theyexhibit in the first layer heteroleptic tetrahedra V5+S3O and isolated Q(2-) anions and in the secondlayer dichalcogenide pairs (Q(2))(2-) withQ = S or Se. Selenide derivatives were attempted by targeting theselective substitution of isolated Q(2-) or (Q(2))(2-) (in distinct layers) or both by selenide,but it systematically led to concomitant and partial substitutionof both sites. A DFT meta-GGA study showed that selective substitutionyields local constraints due to rigid VO3S and pairs. Experimentally,incorporation of selenide in both layers avoids geometrical mismatchand constraints. In such systems, we show that the interplay betweenthe O/S anionic ratio around V5+, together with the presence/natureof the dichalcogenides (Q(2))(2-) and isolatedQ(2-), impacts in unique manners the band gap andprovides a rich background to tune the band gap and the symmetry.