Mechanism of silsesquioxane growth

Abstract

The mechanism of silsesquioxane growth is studied with an insertion mechanism analogous to the one previously proposed for fullerene growth. Isomers of hydridosilsesquioxanes Si_nO_3n/2H_n with different symmetry are presented for n = 24–48 to understand the reaction pathways between highly symmetric structures from n = 24 (D_6d) to n = 36 (D_6h) and n = 48 (D_6d) which can be considered as precursors of nanotubes. A representative calculation for the growth of Si₃₀O₄₅H₃₀ to Si₃₂O₄₈H₃₂ is performed with the MSINDO method. The stepwise reaction involves three intermediates and four transition structures. The studies explain the recent experimental evidence for the existence of silsesquioxanes with up to 38 Si atoms in solution.