High electron affinity triggered by lithium coordination: quasi-chalcogen properties of Li 2 Sn 8 Be.

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 Li 2 Sn 8 Be 2- , has been obtained by decorating endohedral Zintl ion Sn 8 Be 4- with two Li ligands. Its neutral counterpart, namely Li 2 Sn 8 Be, exhibits a high electron affinity of 2.526 eV, which not only exceeds that of the Sn 8 Be cluster but is higher than those of chalcogen elements. Li 2 Sn 8 Be 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, O 2 2- , H 2 O 2 , and Li 2 O 2 can also be obtained with Li 2 Sn 8 Be serving as the building block. The striking resemblance between Li 2 Sn 8 Be 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".