Encapsulation of Mg2 inside a C60 cage forms an electride.

Density functional theory (DFT) based calculations have been carried out for the endohedral encapsulation of magnesium dimer inside fullerene, that is, Mg2 @C60 . It is observed that the minimum energy structure of the Mg2 @C60 system is C2h symmetry. The MgMg bond distance in the Mg2 @C60 system is much shorter than that in the free Mg2 and Mg2 2+ ion. The formation of the endohedral Mg2 @C60 system is thermochemically spontaneous in nature. The natural bond orbital (NBO) analysis showed the presence of an Mg2 2+ fragment with an MgMg bond inside the C60 cage. The electron density descriptors have identified the covalency in the MgMg bond. A non-nuclear attractor (NNA) is present in the middle of the two Mg-atoms. The bonding interaction between the Mg2 and C60 fragments is ionic in nature and the [Mg2 2+ ] and [C60 2- ] represent the bonding pattern in the Mg2 @C60 system. The designed endohedrally encapsulated system behaves as an electride.