Theoretical Investigation of Metallic Heterofullerenes of Silicon and Germanium Mixed with Phosphorus and Arsenic Atoms M-A8E6, A = Si, Ge; E = P, As; and M = Cr, Mo, W.

Recently, metallic heterofullerenes were experimentally prepared from mixed Ge-As clusters and heavier elements of groups 14 and 15. We found that the shape of these heterofullerenes doped by transition metals appears to be a general structural motif for both silicon and germanium clusters when mixing with phosphorus and arsenic atoms. Structural identifications for MSiP, MSiAs, MGeP, and MGeAs clusters, with M being a transition metal of group 6 (Cr, Mo and W), showed that most MAE clusters, except for Cr-doped derivatives CrSiAs CrGeP, and CrGeAs, exhibit a high-symmetry fullerene shape in which metal dopant is centered in a D AE heterocage consisting of six AE pentagonal faces and three AE rhombus faces. The stability of the MAE metallic heterofullerene is significantly enhanced by formation an electron configuration of [1S 1P 1D 1F 1G 2S 2P 2D] enclosing 68 electrons. The AE heterocages give a great charge transfer (∼4 electrons) to centered dopant, establishing subsequently a d configuration for metal, and as a consequence, it induces an additional stabilization of the resulting MEP fullerene in a high-symmetry D shape and completely quenches the high spin of the metal atom, finally yielding a singlet spin ground state.