High electron affinity triggered by lithium coordination: quasi-chalcogen properties of Li₂Sn₈Be

This work puts forward an unusual but rational strategy to design superatoms mimicking the properties of group via elements. A new dianion with closo-configuration, namely Li₂Sn₈Be^2-, has been obtained by decorating endohedral Zintl ion Sn₈Be^4- with two Li ligands. Its neutral counterpart, namely Li₂Sn₈Be, exhibits a high electron affinity of 2.526 eV, which not only exceeds that of the Sn₈Be cluster but is higher than those of chalcogen elements. Li₂Sn₈Be has the potential to form stable ionic compounds with lithium, calcium, and even superalkali and superalkali-earth-metal atoms, and has an oxidation state of -2 therein. Besides, compound analogues of CO, O₂^2-, H₂O₂, and Li₂O₂ can also be obtained with Li₂Sn₈Be serving as the building block. The striking resemblance between Li₂Sn₈Be and oxygen-group elements not only qualifies it for membership of the superatom family, but further collaborates the theoretical framework of the "three-dimensional periodic table".