Fullerenes with four-membered rings

We developed an interest in structural requirements for R4 substructures in fullerenes. The results of this study indicate that a definition of fullerenes which limits consideration to cages consisting solely of R6 and R5 rings may be inadequate to describe the full range of possible fullerene structures and chemistry. We have provided evidence that polyhedral carbon structures with fewer than 60 carbon atoms may actually be stabilized by incorporation of two four-membered rings in the fullerene molecular framework. We find that strain energies are always higher in the R4 = 2 fullereness and that the stabilizing R4 effects are generally due to stabilization of the [pi] systems, even at HMO levels of calculation. 24 refs., 1 fig., 1 tab.