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 MSi8 P6 , MSi8 As6 , MGe8 P6 , and MGe8 As6 clusters, with M being a transition metal of group 6 (Cr, Mo and W), showed that most MA8 E6 clusters, except for Cr-doped derivatives CrSi8 As6, CrGe8 P6 , and CrGe8 As6 , exhibit a high-symmetry fullerene shape in which metal dopant is centered in a D3h A8 E6 heterocage consisting of six A3 E2 pentagonal faces and three A2 E2 rhombus faces. The stability of the MA8 E6 metallic heterofullerene is significantly enhanced by formation an electron configuration of [1S2 1P6 1D10 1F14 1G18 2S2 2P6 2D10 ] enclosing 68 electrons. The A8 E6 heterocages give a great charge transfer (∼4 electrons) to centered dopant, establishing subsequently a d10 configuration for metal, and as a consequence, it induces an additional stabilization of the resulting ME8 P6 fullerene in a high-symmetry D3h shape and completely quenches the high spin of the metal atom, finally yielding a singlet spin ground state.