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 MSi8P6, MSi8As6, MGe8P6, and MGe8As6 clusters, with M being a transition metal of group 6 (Cr, Mo and W), showed that most MA(8)E(6) clusters, except for Cr-doped derivatives CrSi8As6, CrGe8P6, and CrGe8As6, exhibit a high symmetry fullerene shape in which metal dopant is centered in a D-3h A(8)E(6) heterocage consisting of six A(3)E(2) pentagonal faces and three A(2)E(2) rhombus faces. The stability of the MA(8)E(6) metallic heterofullerene is significantly enhanced by formation an electron configuration of [1S(2) 1P(6) 1D(10) 1F(14) 1G(18) 2S(2) 2P(6) 2D(10)] enclosing 68 electrons. The A8E6 heterocages give a great charge transfer (similar to 4 electrons) to centered dopant, establishing subsequently a d(10). configuration for metal, and as a consequence, it induces an additional stabilization of the resulting ME8P6 fullerene in a high symmetry D-3h shape and completely quenches the high spin of the metal atom, finally yielding a singlet spin ground state.