Rational Design of Stable Dianions and the Concept of Super-Chalcogens.

Super-atoms are homo/heteroatomic clusters that mimic the chemistry of atoms in the periodic table. While a considerable amount of research over the past three decades has revealed many super-atoms that mimic group I (alkali metals) and group 17 (halogens) elements, little effort has been made to identify super-atoms that mimic the chemistry of chalcogens, i.e., those belonging to group 16 elements. This is particularly important as super-chalcogens can form the building blocks of new materials, just as super-alkalis and super-halogens form a variety of super-salts with unique properties. Using first-principles calculations and various electron counting rules, some of which have been prevalent in chemistry for a century, we provide a route to the rational design of dianions that are stable in the gas phase. And unlike the group 16 atoms, these super-chalcogens can retain the second electron without spontaneous electron emission or fragmentation. A new class of super-chalcogenides with unique properties could be formed with these super-chalcogens as building blocks.