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 Li2Sn8Be2-, has been obtained by decorating endohedral Zintl ion Sn8Be4- 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, O22-, 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".