Encapsulation of Mg inside a C 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, Mg @C . It is observed that the minimum energy structure of the Mg @C system is C symmetry. The MgMg bond distance in the Mg @C system is much shorter than that in the free Mg and Mg ion. The formation of the endohedral Mg @C system is thermochemically spontaneous in nature. The natural bond orbital (NBO) analysis showed the presence of an Mg fragment with an MgMg bond inside the C 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 Mg and C fragments is ionic in nature and the [Mg ] and [C ] represent the bonding pattern in the Mg @C system. The designed endohedrally encapsulated system behaves as an electride.