Stabilization of large silicon fullerenes and related nanostructures through puckering and poly(oligo)merization

The structure, symmetry, and stability of large Si_nH_n, n=60, 70, 76, 80, and 180 cages and the Si₆₀H₆₀ ligomers: Si₁₂₀H₁₁₆, Si₁₈₀H₁₇₂, and Si₂₄₀H₂₂₈, together with some related “fullerenes” and nanostructures, are studied by ab initio density functional theory and second order Møller-Plesset perturbation theory (for Si₆₀H₆₀). It is shown that large cages, n≥60, can be further stabilized by “puckering” of the Si–Si and Si–H bonds through the endohedral bonding of a number of Si-H pairs without altering the symmetry, in all but the n=60 case. For Si₆₀H₆₀, the symmetry is slightly reduced from I_h to D_5d. Such puckering can also lead to alternative structures of the same symmetry (D_5d for Si₆₀H₆₀), but not necessarily of the same stability. Alternatively, or in parallel, the “oligomerization” (or polymerization) of the fullerenes can also lead to higher stabilization. The present results seem to suggest that chain (oligo)polymerization is more favorable compared to sidewise polymerization, implying some preference for fullerene-structured silicon nanowires. These results are very promising for the study and possible synthesis of such fullerenes and fullerene-based nanostructures.