Ba with Unusual Oxidation States in Ba Chalcogenides under Pressure

The preparation of compounds with novel atomic oxidation states and emergent properties is of fundamental interest in chemistry. As s-block elements, alkali-earth metals invariably show a +2 formal oxidation state at normal conditions, and among them, barium (Ba) presents the strongest chemical reactivity. Herein, we propose that novel valence states of Ba can be achieved in pressure-induced chalcogenides, where it also shows a feature of 5d-elements. First-principles swarm-intelligence structural search calculations identify three novel stoichiometric compounds: BaCh(4) (Ch = O, S) containing Ba2+, Ba(3)Ch(2) (Ch = S, Se, Te) with Ba+ and Ba2+, and Ba(2)Ch (Ch = Se, Te) with Ba+ cations. The pressure-induced drop of the Ba 5d level relative to Ba 6s is responsible for this unusual oxidation state. These compounds display captivating structural characters, such as Bacentered polyhedra and chain-shaped Ch units. More interestingly still, the interaction between two Ba+ ions ensures their structural stability.

Automated summary

The preparation of compounds with novel atomic oxidation states and emergent properties is of fundamental interest in chemistry. BaCh(4) (Ch = O, S), Ba(3)Ch(2) (Ch = S, Se, Te), and Ba(2)Ch (Ch = Se, Te) are three novel stoichiometric compounds of barium with different valence states identified through first-principles swarm-intelligence structural search calculations. The pressure-induced drop of the Ba 5d level relative to Ba 6s is responsible for these unusual oxidation states, and these compounds display captivating structural characters like Ba-centered polyhedra and chain-shaped Ch units.