Evidence for the Superatom–Superatom Bonding from Bond Energies

[Image: see text] Metal clusters with specific number of valence electrons are described as superatoms. Super valence bond (SVB) model points out that superatoms could form the superatomic molecules through SVBs by sharing nucleus and electrons. The existence of superatom–superatom bonding was verified by the shape of their orbitals in former studies. In this paper, another important evidence—bond energy is studied as the criterion for the SVBs using the density functional theory method. In order to get the reliable values of bond energies, the series of Zn–Cu and Mg–Li superatomic molecules composed of two tetrahedral superatoms which do not share their nucleus are designed. Considering the number of the valence electrons in one tetrahedral superatomic unit, (Zn(4))(2)/(Mg(4))(2), (Zn(3)Cu)(2)/(Mg(3)Li)(2), (Zn(2)Cu(2))(2)/(Mg(2)Li(2))(2), and (ZnCu(3))(2)/(MgLi(3))(2) clusters are 8e–8e, 7e–7e, 6e–6e, and 5e–5e binary superatomic molecules with super nonbond, single bond, double bond, and triple bond, respectively, which are verified by chemical bonding analysis depending on the SVB model. Further calculations reveal that the bond energies increase and the bond lengths decrease along with the bond orders in Zn–Cu and Mg–Li systems which is in accordance with the classical nonbond, single bond, double bond, and triple bond in C–H systems. Thus, these values of bond energies confirm the existence of the SVBs. Moreover, electron localization function analysis is also carried on to describe the similarity between the superatomic bonds and atomic bonds in simple molecules directly. This study reveals the new evidence for the existence of the superatom–superatom bonding depending on the bond energies, which gives the new insight for the further investigation of the superatomic clusters.