Fully coordinated silica nanoclusters: (SiO2)N molecular rings.

A new form of finite silica with edge-sharing SiO2 units connected in a ring is proposed. High-level density-functional calculations for (SiO2)(N), N=4-14, show the rings to be energetically more stable than the corresponding (SiO2)(N) linear chains for N>11. The rings display frequency modes in remarkable agreement with infrared bands measured on dehydrated silica surfaces indicating their potential as models of strained extended silica systems. Silica rings, if synthesized, may also be useful precursors for new bulk-silica polymorphs with tubular or porous morphologies.